Buchheit & Laursen - HIT, Solutions to the Programming Puzzle Part I

Author's personal copySports Med (2013) 43:313–338 DOI 10.1007/s40279-013-0029-x REVIEW ARTICLE High-Intensity Interval Training, Solutions to the Programming Puzzle Part I: Cardiopulmonary Emphasis Martin Buchheit • Paul B. Laursen Published online: 29 March 2013 Ó Springer International Publishing Switzerland 2013 Abstract High-intensity interval training (HIT), in a variety of forms, is today one of the most effective means of improving cardiorespiratory and metabolic function and, in turn, the physical performance of athletes. HIT involves repeated short-to-long bouts of rather high-intensity exercise interspersed with recovery periods. For team and racquet sport players, the inclusion of sprints and all-out efforts into HIT programmes has also been shown to be an effective practice. It is believed that an optimal stimulus to elicit both maximal cardiovascular and peripheral adaptations is one where athletes spend at least several minutes per session in their ‘red zone,’ which generally means reaching at least 90 % of their maximal oxygen uptake _ O2max). While use of HIT is not the only approach to (V improve physiological parameters and performance, there has been a growth in interest by the sport science community for characterizing training protocols that allow athletes to maintain long periods of time above 90 % of _ O2max (T@V _ O2max). In addition to T@V _ O2max, other V physiological variables should also be considered to fully characterize the training stimulus when programming HIT, including cardiovascular work, anaerobic glycolytic energy contribution and acute neuromuscular load and musculoskeletal strain. Prescription for HIT consists of the manipulation of up to nine variables, which include the work interval intensity and duration, relief interval intensity and duration, exercise modality, number of repetitions, number of series, as well as the between-series recovery duration and intensity. The manipulation of any of these variables can affect the acute physiological responses to HIT. This article is Part I of a subsequent II-part review and will discuss the different aspects of HIT programming, from work/relief interval manipulation to the selection of exercise mode, using different examples of training cycles from different sports, with continued reference to _ O2max and cardiovascular responses. Additional proT@V gramming and periodization considerations will also be discussed with respect to other variables such as anaerobic glycolytic system contribution (as inferred from blood lactate accumulation), neuromuscular load and musculoskeletal strain (Part II). M. Buchheit ASPIRE, Football Performance & Science Department, Academy for Sports Excellence, Doha, Qatar M. Buchheit (&) Physiology Unit, Sport Science Department, ASPIRE, Academy for Sports Excellence, P.O. Box 22287, Doha, Qatar e-mail: [email protected]; [email protected] P. B. Laursen High Performance Sport New Zealand, Auckland, New Zealand P. B. Laursen Sport Performance Research Institute New Zealand (SPRINZ), Auckland University of Technology, Auckland, New Zealand 1 Introduction With respect to prescribing training that improves performance, coaches know that ‘‘there’s more than one way to skin the cat.’’[1] Recent reviews [1, 2] have highlighted the potential of varying quantities of both high-intensity interval training (HIT) and continuous high-volume, lowintensity training on performance in highly trained athletes. While there is no doubt that both types of training can effectively improve cardiac and skeletal muscle metabolic function, and that a dose of both types of training are important constitutes of an athlete’s training programme, Author's personal copy 314 M. Buchheit, P. B. Laursen this review will focus solely on the topic of HIT. Indeed, a number of studies in this area have emerged over the last decade, and it is perhaps not surprising that running- or cycling-based HIT is today considered one of the most effective forms of exercise for improving physical performance in athletes [3–6]. ‘‘HIT involves repeated short-tolong bouts of rather high-intensity exercise interspersed with recovery periods’’ [3], and has been used by athletes for almost a century now. For example, in 1920, Paavo Nurmi, one of the best middle- and long-distance runners in the world at that time, was already using some form of HIT in his training routines. Emil Zatopek contributed later in the 1950s to the popularization of this specific training format (see Billat [3] for a detailed history of HIT). The progressive emergence of this training method amongst elite athletes is the first evidence of its effectiveness (i.e. ‘best practice’ theory [2]). More recently, the use of sprints and all-out efforts has also emerged, both from the applied (team sport) field and the laboratory [7–9]. These particularly intense forms of HIT include repeated-sprint training (RST; sprints lasting from 3 to 7 s, interspersed with recovery periods lasting generally less than 60 s) or sprint interval training (SIT; 30 s all-out efforts interspersed with 2–4 min passive recovery periods). Following pioneering experiments by Hill in the 1920s (Hill included intermittent exercises in his first studies [2]), Astrand and co-workers published several classical papers in the 1960s on the acute physiological responses to HIT, which created the first scientific basis for long [10] and short [11, 12] duration intervals. Studies by Balsom et al. followed in the 1990s, emphasizing all-out efforts [13]. As will be detailed in the review, most of the scientific work that followed these studies over the past 20–50 years has been an extension of these findings using new technology in the field (i.e. more accurate and portable devices). However, the important responses and mechanisms of HIT had already been demonstrated [10–12]. It has been suggested that HIT protocols that elicit _ O2max), or at least a very high maximal oxygen uptake (V _ O2max, maximally stress the oxygen transpercentage of V port and utilization systems and may therefore provide the _ O2max [5, 14, 15]. most effective stimulus for enhancing V While evidence to justify the need to exercise at such an intensity remains unclear, it can be argued that only exer_ O2max allow for both large motor unit cise intensities near V recruitment (i.e. type II muscle fibres) [16, 17] and attainment of near-to-maximal cardiac output (see Sect. 3.2), which, in turn, jointly signals for oxidative muscle fibre adaptation and myocardium enlargement (and hence, _ O2max). For an optimal stimulus (and forthcoming carV diovascular and peripheral adaptations), it is believed that athletes should spend at least several minutes per HIT session in their ‘red zone,’ which generally means attaining _ O2max [3, 5, 15, 18]. an intensity greater than 90 % of V Consequently, despite our limited understanding of the dose-response relationship between the training load and training-induced changes in physical capacities and performance (which generally shows large inter-individual responses [19, 20]), there has been a growing interest by the sport science community for characterizing training protocols that allow athletes to maintain the longest time _ O2max (T@V _ O2max; see Midgley and McNaugh[90 % V _ O2max, however, ton [14] for review). In addition to T@V other physiological variables should also be considered to fully characterize the training stimulus when programming HIT [21–23]. Any exercise training session will challenge, at different respective levels relative to the training content, both the metabolic and the neuromuscular/musculoskeletal systems [21, 22]. The metabolic system refer to three distinct yet closely related integrated processes, including (1) the splitting of the stored phosphagens (adenosine triphosphate [ATP] and phosphocreatine [PCr]); (2) the nonaerobic breakdown of carbohydrate (anaerobic glycolytic energy production); and (3) the combustion of carbohydrates and fats in the presence of oxygen (oxidative metabolism, or aerobic system) [184]. It is therefore possible to precisely characterize the acute physiological responses of any HIT session, based on (a) the respective contribution of these three metabolic processes; (b) the neuromuscular load; and (c) the musculoskeletal strain (Fig. 1, Part I). Under these assumptions, we consider the _ O2) data, but also cardiorespiratory (i.e. oxygen uptake; V cardiovascular work [24–27]), stored energy [28, 29] and cardiac autonomic stress [30–33] responses as the primary variables of interest when programming HIT sessions (review Part I). By logic, anaerobic glycolytic energy contribution and neuromuscular load/musculoskeletal strain are therefore likely the more important secondary variables to consider when designing a given HIT session (Part II). Several factors determine the desired acute physiological response to an HIT session (and the likely forthcoming adaptations) [Fig. 1]. The sport that the athlete is involved in (i.e. training specificity) and the athlete’s profile or sport specialty (e.g. an 800 m runner will likely favour a greater proportion of ‘anaerobic-based’ HIT compared with a marathon runner [6]) should first be considered in relation to the desired long-term training adaptations. Second, and more importantly on a short-term basis, training periodization has probably the greatest impact on the HIT prescription. Many of the desired training adaptations are likely training cycle dependent (e.g. generic aerobic power development in the initial phase of the preseason vs. sportspecific and more anaerobic-like HIT sessions towards the However. While some HIT formats can be used to match different response categories (e. (4) metabolic as for (3) plus a certain degree of neuromuscular load. short intervals when properly manipulated can match into categories 1–4). (2) metabolic as for (1) but with a certain degree of neuromuscular strain. the ability of the coach to understand the isolated acute responses to various HIT formats may assist with selection of the most appropriate HIT session to apply. will achieve a similar metabolic and/or neuromuscular training adaptation outcome. (3) metabolic as for (1) but with a large anaerobic glycolytic energy contribution.e. the physiological strain associated with a given HIT session needs to be considered in relation to the demands of other physical and technical/ tactical sessions to avoid overload and enable appropriate adaptation (i. 12]. especially for team and racquet sport athletes. for athletes training twice a day.e. the number of intervals. There are likely several approaches (i.e. Exercise modality (i. surrogate of anaerobic glycolytic energy release RST repeated-sprint training. running vs.g. cardiopulmonary and/or neuromuscular responses. i. responses are more difficult to . The six different types of acute responses are categorized as (1) metabolic. cardiopulmonary system and oxidative muscle fibres. SIT spring interval training start of the competitive season in team sports). Then. and/or in team sport players training a myriad of metabolic and neuromuscular systems simultaneously [34].e. SIT for example can only match category 5. or straight line vs. but it is clear that it represents a key variable to consider when programming HIT. (5) metabolic with essentially an important anaerobic glycolytic energy contribution and a large neuromuscular load. Additionally. Category 6 is not detailed in the present review since it does not fit into any particular type of HIT. When more than one variable is manipulated simultaneously. uphill or change of direction running) has to date received limited scientific interest. HIT format) that. The manipulation of each variable in isolation likely has a direct impact on metabolic. at the right place and time. the number of series and between-series recovery durations and intensities determine the total work performed.Author's personal copy HIT Programming: Cardiopulmonary Emphasis 315 Fig. The intensity and duration of work and relief intervals are the key influencing factors [10. and (6) eliciting a high predominant neuromuscular strain. [La] blood lactate accumulation. HIT high-intensity interval training. maximize a given training stimulus and minimize musculoskeletal injury risk). cycling or rowing. 2 [35]). but eliciting essentially large requirements from the O2 transport and utilization systems. 1 Decision process for selecting an HIT format based on the expected acute physiological response/strain. considered in isolation. At least nine variables can be manipulated to prescribe different HIT sessions (Fig. It is likely. in Part I of this review. using incremental test parameters is far more objective. which may assist to individualize HIT prescription for different types of athletes. We provide. such as cardiovascular responses.g.Author's personal copy 316 Fig. the different aspects of HIT programming. erence to T@V otherwise stated). several approaches exist to control and individualize exercise speed/power accordingly. Since the main goal of HIT sessions is _ O2max. gender. it remains progressing with respect to T@V unclear which combination of work-interval duration and intensity. and not a systematic review. our methods included a selection of the papers we believed to be most relevant in the area. sedentary or cardiac patients). While our understanding of how to manipulate these variables is _ O2max [14]. time spent C90 % V _ O2max. and interpreted using Hopkins’ categorization criteria. but without using physiological markers such as the speeds . from work/relief interval manipulation to the selection of exercise modality. ‘medium’.2. with continued ref_ O2max (i. Finally. 2 Schematic illustration of the nine variables defining a HIT session adapted from Buchheit [35]. 2. We will discuss these points and illustrate why. Standardized differences (or effect sizes. and likely more accurate and effective at achieving desired performance outcomes. Acute responses to running-based HIT were given priority focus. Laursen Work modality Relief Intensity Duration Work Duration Series Time between series # of series Between-series recovery intensity Series duration predict. Buchheit.1 The Track-and-Field Approach To programme HIT for endurance runners. rowing. if any. 1. 0.g.2 and [2 are considered ‘small’. coaches have traditionally used specific running speeds based on set times for distances ranging from 800 m to 5000 m. etc. Additional programming considerations will also be discussed with respect to other variables. in our opinion. B. Considering that long-term physiological and performance adaptations to HIT are highly variable and likely population-dependent (age. 20].e. Different examples of training cycles from different sports will be provided in Part II of the present review. with the exception of under-water activities that may require a specific programming approach [36].6. however. ‘large’ and ‘very large’ effects. is most effective at allowing an individual _ O2max while ‘controlling’ for the to spend prolonged T@V level of anaerobic engagement [3] and/or neuromuscular load (review Part II). the reader is referred to recent reviews [37] and original investigations [38–40]. greater than the second ventilatory threshold or maximal lactate steady state) were considered. where 0. 2 Prescribing Interval Training for Athletes in the Field To prescribe HIT and ensure that athletes reach the required intensity. only HIT sessions to improve the determinants of V performed in the severe intensity domain (i. e.e. P. since the factors are inter-related. training status and background) [19. respectively [42]. since the largest quantity of literature has used this exercise mode. that the manipulation of these same HIT variables has comparable effects in other sports (or exercise modes.). cycling. we believe that the present recommendations are essentially appropriate for moderately trained to elite athletes. As this was a narrative. practical. providing general recommendations for the more efficient HIT format is difficult. however. For special populations (e. HIT highintensity interval training Intensity M. ES [41]) have been calculated where possible to examine the respective effects of the manipulation of each HIT variable. e. The translation and application of the track-and-field method to other sports is. difficult. lactate or ventilatory thresholds associated with V [3]. 51]. the speed maintained over 800–1. for whom best running times on several set distances are known. MLSS maximal lactate steady state. 3 Intensity range used for the various run-based HIT formats. MSS maximal sprinting speed. 52. ASR anaerobic speed reserve. VO maximal oxygen uptake. this approach tends to be reserved for highly experienced coaches and well trained athletes.500 m to 2. run based) but more controlled HIT formats at certain times of the season or for specific player needs. 3) of the athlete can be used to ‘shape’ the HIT session.Test peak incremental test speed . 5 min 30 s of the 8min game) [50]. and following the important principle of training specificity. 10–60 s) the reference running time will be a percentage of the time measured over a maximal 100–400 m sprint. and still are. is that it does not allow the coach to consciously manipulate the acute physiological load of the HIT session. 1. SSGs have limitations that support the use of less specific (i.e. 50. that coaches and athletes have been. 2. be precisely standardized. SSG) [43–46] or skill-based [47. suggesting a possible ceiling _ O2max development in fitter players. The acute physiological load of an SSG session can be manipulated by changing the technical rules [54]. so that each run can be performed in accordance with the athlete’s (maximal) potential. 53]. 57]). using the track-and-field approach for non-track-andfield athletes is unlikely to be appropriate.e. Fig. _ 2max minimal running speed vVO _ 2max. Additionally. but the overall load cannot.Author's personal copy HIT Programming: Cardiopulmonary Emphasis 317 _ O2max. so-called small sided games.e. Additioneffect for V ally. an observation that should humble the exercise physiologist. average V _ sely related to V O2max [50]. both maximal sprinting and aerobic speeds.000 m can be used to calibrate longer intervals (e. and precisely target a specific adaptation (i. While for short intervals (i. 2–4 to 6–8 min). practical or effective.g. reaching and maintaining an elevated cardiac filling is believed to be necessary to improve maximal cardiac Fig. It is worth mentioning. highly successful using this approach. T@V _ O2max V during an SSG in national-level handball players was achieved for 70 % of the session (i. however. game. VD50 required to elicit VO speed half way between _ O2max and MLSS. For example.e. While understanding of the _ O2 responses to SSG is limited [44. when there is a need to improve a physiological quality and not just to prepare for a race). however. RST repeatedsprint training. The attraction of this method is that the entire locomotor profile (i. and the between-player variability in the (cardiovascular) responses is higher than more specific run-based HIT [49]. Vcrit vV critical velocity. Within-player responses to SSG are highly variable (poor reproducibility for blood lactate [coefficient of variation (CV): 15–30 %] and high-intensity running responses [CV: 30–50 %] [56. Although the effectiveness of such an approach has been shown [43. 48] conditioning has received an exponential growth in interest [49].10-m tall basketball player that has never run more that 40 s continuously on a court before? Thus.(i. During _ O2 was shown to be inveran SSG in handball. Fig. however. by default. VInc. SIT sprint _ 2max interval training. the number of players and pitch size [55]. VIFT peak speed reached at the end of the 30–15 Intermittent Fitness Test.e. how might a coach determine the expected 800-m run time for a 2.2 The Team Sport Approach Due to the technical/tactical requirements of team sports.000–3. The disadvantage of this approach. 46. biomechanical and psychological [76] stress/fatigue imposed on the body during exercise [77]. Thus.e. it is difficult to imagine how an athlete would practically control or adjust exercise intensity during an interval. since it does not allow for the precise manipulation of the physiological response to a given HIT session. and strenuous exercise is’’ [74]. RPE is a universal ‘exercise regulator’. Additionally. limit the maintenance of a high stroke volume (SV) throughout the exercise and compromise long term adaptations [60] (see Sect.Author's personal copy 318 M. especially for athletes running at high speed. This could limit the ability to target a specific adaptation (i. the V speed [63]) relationship also tends to be higher during an SSG compared with generic running.2). 2. blood lactate levels and work output between HR. i. 50. which is much slower to respond compared _ O2 response [70]. V (HRmax) [21. There is also some evidence to suggest that the ability to adjust/evaluate . the session goal and external considerations related to training periodization. and suggests that assessment of cardiopulmonary responses during an SSG (and competitive games) using HR may be _ O2/speed [50] (and HR/ misleading [63]. 3. 62]). where viewing HR from a watch is difficult. Buchheit. _ O2/heart Compared with generic run-based exercises. The intensity selected is typically the maximal intensity of exercise perceived as sustainable (‘hard’ to ‘very hard’. RPE responses are gender-independent [78] and comparable during free versus constant pace exercise [79]. B. irrespective of locomotor mode and variations in terrain and environmental conditions. this is not always the case. This confirms the aforementioned possible limitations with respect to SV enlargement. HR cannot inform the intensity of physical work performed above the _ O2max. In practice. 59]. relative to the combined physiological [75]. Finally.3 Heart Rate-Based Prescription Heart rate has become the most commonly measured physiological marker for controlling exercise intensity in the field [67]. and might also be problematic in a team sport setting (as discussed in the three preceding sections). the first benefit of RPE-guided HIT sessions [69. in turn. While this method of training is often considered to be highly specific. the temporal dissociation _ O2. coaches generally prescribe independent variables such as the duration or distance of work and relief intervals [71]. This is related to the well-known HR lag at exercise onset. its effectiveness for controlling or adjusting the intensity of an HIT session may be limited. Laursen function [58. while HR is expected to reach maximal values ([90–95 % HRmax) for exercise at or below the speed/power associated _ O2max. 1). the athlete can self-regulate their exercise intensity. The repeated changes in movement patterns and the alternating work and rest periods during an SSG might therefore induce variations in muscular venous pump action. It has also been shown that substantially different exercise sessions (as assessed by accumulated blood lactate levels during run-based HIT [71] and by running speed during an SSG [63]) can have a relatively similar mean HR response. 1–2 min) [69] intervals. While the specific roles (or contributions) played by varying biological afferents and other neurocognitive processes involved with the selection of exercise pace based on effort are still debated (see viewpoint/counterpoint [73]). While this ratio is generally close to 1 during run-based long intervals _ O2 at 95 % V _ O2max for HR at 95 % of maximal HR (i. C6 on a CR-10 Borg scale and C15 on a 6–20 scale) and is based on the athlete’s experience. since this can create an overestimation of the actual work/physiological load that occurs during recovery periods [69]. In return. P.e.e. The RPE method does have limitations. Fig. Further. it has been shown to promote the same physiological adaptations as an HR-based programme over 6 weeks in young women [80]. authors have reported values at 79 % _ O2max and 92 % HRmax during basketball drills [44] and V _ O2max and 72 % HRmax during a five-a-side at 52 % V indoor soccer game [51]. possibly due to higher muscle mass involvement.4 Rating of Perceived Exertion-Based Prescription Prescribing the intensity of HIT bouts using the rating of perceived exertion (RPE) method [72] is highly attractive because of its simplicity (no need to monitor HR) and versatility. the V rate (HR) ratio (which can be used with caution as a surrogate of changes in SV during constant exercise when the arteriovenous O2 difference is deemed constant [61]) is also likely lower during an SSG [44. since during competitive games players have often more space to run and reach higher running speeds (up to 85–90 % of maximal sprinting speed [64– 66]) for likely similar metabolic demands. heavy. Setting exercise intensity using HR zones is well suited to prolonged and submaximal exercise bouts.e.e. While more research in trained athletes is needed to confirm the efficacy of RPEguided training sessions. 2. HR inertia at exercise with the V cessation (i. V during HIT limits our ability to accurately estimate intensity during HIT sessions using HR alone. HR recovery) can also be problematic in this context. however. 51]. Finally. however. this is not always the case. which represents a speed/power associated with V large proportion of HIT prescriptions [3–5]. especially for very with V short (\30 s) [68] and medium-long (i. Using this approach. which can. Further. RPE responses may reflect ‘‘a conscious sensation of how hard. 71] is that they do not require any knowledge of the athletes’ fitness level (no test results needed). _ O2max and VInc.5 % (90 % confidence limits: 3. is probably the preferred method. 90]) as a useful reference intensity to programme HIT _ O2max method is that it [3–5].Test. 89]. worth noting that using vV the reference running speed is essentially suitable for long _ O2max (90–105 %). A 5-min exhaustive run [101].e. 3. either on the track. but V/pInc. 3. Billat and D.5 % for UM-TT VInc. Since v/pV _ O2max. the final (peak) incremental test speed/power reached at the end of these tests (V/pInc. a number of v/pV different ways. the importance of other physiological attributes should be . For training prescription.5 % and 3 % for treadmill VInc. 98]. however.Test in well trained male distance runners [106] and recreational runners [104]. however. or estimated. for trained runners able to run at vV 3) _ O2max is also method-[90] and protocol-dependent vV _ O2max [88.W. The attractiveness of the v/pV _ O2max and the represents an integrated measure of both V energetic cost of running/cycling into a single factor. A mathematically estimated vV _ likely to be lower than a measured vV O2max [93] that is also lower than VInc. 1–2 % for the 5-min test in a heterogeneous sporting population [107]. Additionally. Similarly. These differences must be acknowledged since small differences in the prescribed work intensity have substantial effects on acute HIT responses. the University of Montreal Track Test (UM-TT [87]) is the protocol most commonly used with athletes [94. since the average time _ O2max has been reported to range to exhaustion at vV _ O2max calculated from 4 to 8 min [89.0.V/pInc. on a treadmill or using an ergometer.Test (as examined The reliability of vV _ O2max using CVs) has been shown to be good: 3 % for vV in moderately trained middle. VInc. very practical in 4) the field since it is largely correlated with distance running performance [99] and match running capacity in team sports (but for some positions only) [98. 100]. irrespec_ O2max.94) and on a ramp treadmill test (r = 0. Direct measurement (i. protocols tive of the method used to determine vV with longer-stage durations tend to elicit lower speed/ power values [103].Test is. while being slightly (i.Test [89. in addition to not requiring sophisticated apparatus. and finally. It anaerobic contribution necessary to elicit V _ O2max or VInc. since. unpublished results]) for Vam-Eval VInc. either with [91] ical running speed for a given V _ or without [92] resting V O2 values.Test reached in the UM-TT (r = 0. 4.Test in 65 highly trained young football players. For (2–6 min) intervals ran around vV sub.90 [87]). 83]. The individual cost of running to calculate a theoret_ O2max. 104]. respectively. and may only be valid _ O2max for &5 min. which only differs from the UMTT due to its smoother speed increments and shorter intercones distances. it makes lowest speed/power needed to elicit V intuitive sense for this marker to represent an ideal reference for training [5. 2. being directly representative of an athletes’ loco_ O2max is theoretically the motor ability [89]. erally a greater v/pV Measurement of VInc. exercise-intensity. however.Author's personal copy HIT Programming: Cardiopulmonary Emphasis 319 exercise intensity based on RPE may be age. These two distinct speeds/powers are v/pV strongly correlated (r [ 0.Test in moderately trained athletes [87]. with individuals be 5–10 % greater than v/pV possessing greater anaerobic reserves presenting gen_ O2max . The vV from this test has been shown to be largely correlated with the VInc.L. On the track. respectively. less likely to _ O2max with variations in protopresent impairments in vV col.1 mL/min/kg despite an increase in running speed of 1 km/h [93]).Test as is. fitness[82.Test) is only an approximation of _ O2max. 15. the physiologists V. 91] is [103]. Hill popularized the _ O2max (so-called speed (or power) associated with V _ O2max or maximal aerobic speed/power [MAS/MAP] v/pV [89. 2. hence. The vV estimated via the 5-min test is.[81].Test difference. vV also appears to be inversely related to the terrain or treadmill slope [105]. 95]. however.and supramaximal training intensities.and long-distance runners [68].e.97) [101].and pleasure-[84] dependent.Test can _ O2max. likely influenced by pacing strategies. 1 km/h range) slower and faster _ O2max than these velocities. Since _ O2max during incremental tests requires the ‘true’ v/pV _ O2 measures to determine the lowest speed/power V _ O2max (generally defined as a plateau in that elicits V _ V O2 or an increase less than 2. has also received growing interest since it is easier to administer in young populations and/or non-distance running specialists [97.5 Velocity/Power Associated with Maximal Oxygen _ O2max) Uptake (V Following early works in the 1970s and 1980s [85–88]. the tests account for the _ O2max [108]. _ O2max can be determined. pulmonary gas exchange [93]) during ramp-like incremental running/cycling tests to exhaustion. 102]. while larger speed/power increments _ O2max result in higher-speed/power values. although the Vam-Eval [96]. Endurance-trained athletes are likely able to tolerate longer stages and therefore. as determined in the field with the UM-TT [87] or the Vam-Eval [96]. Methods include using the following: 1) 2) _ O2 and running The linear relationship between V speed established at submaximal speeds [88].1 [Buchheit M. is therefore a product of those above-mentioned abilities. 3) is often not fully taken into (MSS) and vV account by coaches and scientists in their training prescription. but to the training sessions commonly performed in intermittent sports [116]. 115]. despite a similar vV during an HIT session they exercise at a similar percentage _ O2max.7 Peak Speed in the 30–15 Intermittent Fitness Test While using the ASR to individualize exercise intensity for supramaximal runs might represent an improved alterna_ O2max or VInc. in turn. HIT high-intensity interval _ 2max minimal running speeds associated with maximal training. Buchheit. slow and unfit athletes use a greater proportion of their ASR. the exercise will actually involve a different proportion of their ASR. the responses to these forms of HIT appear related to an individual’s (1) metabolic inertia (e. ASR has only recently been considered in relation to repeated-sprint performance [114. The following section highlights the different options available for the prescription of supra_ O2max). it appears that. 116]. In many sports.Test for individualizing HIT with COD in well trained team sport players [94]. P. 5).or racquet-based specific HIT sessions. 118. deceleration.Author's personal copy 320 M. the measurement of MSS (and ASR) should be vV considered for individualizing training intensity during supramaximal HIT [110. While these studies have used continuous exercise. Athlete B with a greater ASR will work at a lower percentage of his ASR. which prevents the standardization of training load. 2. and COD abilities [94.g. the 30–15 Intermittent Fitness Test (30–15IFT) was developed for intermittent exercise and change of direction (COD)-based HIT prescription [35. using an empirical prediction model. Fig. While the peak speeds reached in the different Yo-Yo tests [120] (e. it still does not tive over that of vV capture an overall picture of the different physiological variables of importance during team.g. While track-and-field (running) coaches have indirectly used this concept for years to set the work interval intensity (as discussed in Sect. The 30–15IFT _ O2. but addiwas designed to elicit maximal HR and V tionally provide measures of ASR. vVO oxygen uptake physiological recovery capacities during each relief interval. endurance capacity (or the _ O2max over capacity to sustain a given percentage of vV time [109]) and anaerobic power/capacity [110] are likely to influence time to exhaustion and. and will therefore achieve a lower exercise load compared with Athlete A [116]. when Billat and co-workers [110] showed that time to _ O2max were better related exhaustion at intensities above vV _ O2max. in contrast to VIFT [35]. If MSS ability. For instance. VIFT. training at intensities [ vV 2. the difference between maximal sprinting speed _ O2max. which results in a different physiological demand. 116]. and in turn. 2. a different exercise tolerance [116]. Laursen considered. 4 Illustration of the importance of ASR for two athletes _ O2max.Test (and vV dent [121]. HIT is performed indoors and includes repeated very short work intervals (\45 s). B. in addition to the proportion of the ASR used. to the ASR and/or MSS. and its reliability is good.1).e. Therefore. its _ O2max) is speed-depenrelationship with VInc. acceleration. and likely limits the ability to target specific physiological adaptations [94]. This implies that. and (3) change of direction ability (since indoor HIT is often performed in shuttles) [94. _ O2 kinetics) at the onset of each short interval. the 30–15IFT is highly specific. than to vV [111–113] demonstrated. When running at vYo-YoIR1. fitter athletes run below their vV VIFT has been shown to be more accurate than VInc. repeated effort ability. 94. To overcome the aforementioned _ O2max and limitations inherent with the measurement of vV ASR. 4 [116]). while _ O2max (Fig. For instance. In practice. not to a specific sport. Bundle et al. Fig. (2) V Fig. 116]. two athletes can present with clearly different _ O2max (Fig. as is generally implemented in the field (e. 119]. maximal training (i. but possessing similar running speeds associated with vV different maximal sprinting speeds. the physiological responses. Programming HIT without taking these variables into consideration may result in sessions with different aerobic and anaerobic energy demands. of vV see [117]). vYo-YoIR1 cannot be directly used for training prescription since. In other words. in addition to _ O2max. with the typical . During an HIT session.6 Anaerobic Speed Reserve Consideration for an individual’s anaerobic speed reserve (ASR. vYo-YoIR1 for the Yo-Yo Intermittent Recovery Level 1) and VIFT have likely similar physiological requirements [221]. The final speed reached during the 30–15IFT.g. only the VIFT can be used accurately for training prescription.Test. ASR anaerobic speed reserve. its scientific basis and interest was only brought forth merely a decade ago. that the proportion of ASR used could determine performance during all-out efforts lasting between a few seconds and several minutes. Finally. 5). _ O2max during the 90 % and 140 % conditions was T@V trivial (i. the 30–15IFT permits improved precision of programming by individualizing the intensity of the prescribed interval bouts around intensities ranging from 85 % to 105 % of VIFT [43. Also of note. variation in V make comparison between studies difficult. T@V numerous methodological limitations that need to be considered to interpret the findings shown from the different studies [68. SIT) duration sprints.1. 100 %]). \20 s on average). RST) or long (30–45 s sprints.8) [122]. 3). 120 % and 140 % of their _ O2max (17 km/h) [130]. personal data [35]). Not surprisingly. Fig. 128]. 103. ning. performed around vV VIFT constitutes the upper limit for these exercises (except for very short intervals and all-out repeated-sprint training).e. vYoYoIR1 peak running speed reached at the end of the Yo-Yo intermittent recovery level 1 test error of measurement (expressed as CV) shown to be 1. 50. it is necessary to ‘adjust’ the percentage of VIFT used when programming. VIFT speed reached at the end of the 30–15 Intermittent Fitness Test. 5 Relationships (90 % confidence limits) between the VIFT. including long intervals. since VIFT is _ O2max and/or VInc. they can be prescribed without the need to pre-test the individual (i. overground run_ O2max and vV _ O2max. for minimal V _ 95 %.79. V O2max minus 2. through short intervals and repeated-sprint sequences _ O2 responses of (RSS. 0. and highlights how changes in HIT variables can impact the _ O2max [21. 123–125]. since pulmonary V O2 responses may actually integrate both cardiovascular and muscle metabolic (oxidative) responses to HIT sessions. 127.e. 129]. from long intervals to SIT sessions. 119].88) y = 0.86) y = 0.8 y=x 13 14 15 16 17 18 19 20 VInc. The withinstudy effects of HIT variable manipulation on the observed _ O2max can. Thus.6 % (95 % CL 1. six physical-education students performed four separate runs at 90 %. vYo-YoIR1.1 Maximizing the Time Spent at or Near V 24 10 12 14 16 18 20 22 VInc. 1. In practical terms.8 All-Out Sprint Training Repeated all-out sprinting efforts have received a marked growth in research interest lately [9.Test 2–5 km/h (15–25 %) faster than vV [35.1.e. provide insight towards underT@V standing how best to manipulate HIT variables.4. upper panel (Buchheit M. _ O2max is not specifically needed to calibrate the intensity). Figure 6 illustrates the V four distinct HIT sessions. lower panel [121] and VInc.Author's personal copy HIT Programming: Cardiopulmonary Emphasis 321 a 24 22 20 All pooled n = 141 r = 0. 2.57.1 ml/min/kg. 4]. smoothing technique]. 50. In addition to methodological considerations between studies (treadmill vs.Test peak incremental test speed.Test (km/h) b vYo-Yo IR1 (km/h) 20 19 18 17 16 15 14 13 12 12 Male n = 14 r = 0. Since such exercise is consistently performed ‘all-out’. 126].79 (0. 100–120 % [3.Test (km/h) Fig. time to vV exhaustion was inversely related to running intensity.84 (0.8x + 6 y=x VIFT (km/h) 18 16 14 12 10 Male Female these sessions can be divided into either short (3–10 s. 0. There are. determination criteria for both V data analysis [averaging. threshold _ O2 values considered as maximal [90 %. however. work intensity _ O2max is required to elicit maximal V _ O2 close to v/pV responses. v/pV 3 Acute Responses to Variations of Interval Training _ O2max 3. but reached substantially . _ 2) Responses to Long Intervals 3. Fig. 3).1. however.1 Oxygen Uptake (VO 3.Test. 116.4x + 9. differences in the reliability level of analysers and intra-day subject _ O2max. In the present review. VInc. 100 %. V _ O2 kinetics and times to exhaustion.1 Exercise Intensity during Long Intervals During a single constant-speed or power exercise. In an attempt to determine the velocity associ_ O2max during a run to exhausated with the longest T@V tion. While HIT is generally _ O2max (i. we integrate recently published work and _ O2 responses to provide a comprehensive analysis of the V different forms of HIT. _ O2max We lead off this review with data related to T@V _ (reviewed previously [14]). Slightly lower intensities (C90 % v/pV can also be used when considering repeated exercise bouts _ O2 is likely to (as during HIT sessions). Percentages (mean ± SD) refer to _ O2max relative to the total session time.1. its interval duration must at _ O2max. V _ O2 kinetics are generally V affected by exercise intensity [139]. B. but use inter_ O2max) vals or sets. middle-distance runners did not manage to reach _ O2max while running at 92 % of vV _ O2max [131]. between the maximal lactate steady state and vV _ vD50. P. V _ O2max interval duration \ time needed to reach V _ O2max values is usually not reached on the first interval. the presence and type of pretrial V warm-up).2) RPE:16. HIT high-intensity interval training. 137] to 40 % [104]). VO _ 2max time spent above 90 % or maximal oxygen uptake. 134]) the first intervals (that accelerates V _ O2 slow component [10]. RPE rating of _ 2max perceived exertion.7). 147] than V Distance (m) Time (min) 83(55)% 6000 . [La] blood lactate concentration. &92–93 % of vV O2max [130]) via the development _ O2 slow component [10] is likely fitness-dependent of a V [132] (with highly trained runners unlikely to reach _ O2max).2 Time-to-Reach VO _ Interval Duration If V O2max is to be reached during the first interval of a sequence.2) 5000 4000 3000 2000 1000 0 5x(3min[90% vVO2max]/90s[0%]) 1 3x(2x(2min[100% vVO2max]/2min[50% vVO2max])) 3 5 0 5x(5min[92% vVO2max]/2. vVO 95 % of V _ O2max V ‘larger’ values at 100 % and 120 %: mean ± standard deviation 190 ± 87 (57 % of time to exhaustion. athletes do not exercise to exhaustion. total distance Fig.7(1. in pracT@V tice. be reached during consecutive intervals. Buchheit. However. with some studies reporting relationships [141–143]. The variable has been shown to range from 97 s [138] to 299 s [131] and has a high intersubject variability (20–30 % [131. 6 Mean ± SD of total session time. 135. however.8) 9000 Total distance Distance >90% vVO2max 8000 7000 25 20 15 10 43(13)% 26(15)% 38(21)% 24(9)% 20(14)% 70(9)% 70(19)% N/A 100% 34(12)% 67(30)% RPE:15. 135–138]. 131.9(2. during an HIT session to elicit V _ 2max and Maximizing Long3. and others showing no correlation [144–146].2) M. V can. Laursen 45 40 35 30 Session time T@VO2max (90%) T@VO2max (95%) RPE:13. as during typical HIT sessions (work _ O2max).5(2.5(2) [La]: 5. training status [141. accelerated during running compared with cycling exercise [140] and faster in _ O2 trained individuals [141]. as the determination of vD50 is V impractical in the field.5(2. T@VO _ 2max minimal running speed associated with _ O2max. The V _ O2max during a single run at the velocity ability to reach V _ O2max (i.4) [La]: 8. N/A not available. In another study. Thus. The relationship between V _ kinetics at exercise onset and V O2max. suggesting _ O2 kinetics at exercise onset is more related to that the V _ O2max per se. and distance ran above T@V _ O2max relative to the total distance ran. ES [ ?1. since interval V _ O2 increase with repetitions with the development of a V slow component [10]. the variability is consistent with those shown in _ O2 kinetics at exercise onset. RPE and [La]. ES [ ?2. 2 [127].e. 90 % of vV mmol/L) are provided as mean ± SD when available. however.Author's personal copy 322 [La]: 6. As suggested by Astrand in the 1960s [10].1.5min[46% vVO2max]) 2 3min45[SSG]/30s[0%]/3min45[SSG] 4 _ O2max. While methodological differences could explain some of these dissimilarities (whether 95 % or 100 % of _ O2max is considered. is less clear.8) and 73 ± 29 s (59 %.8(2. exercise intensity does not need to be maximal _ O2max. In addition. least be equal to the time needed to reach V with short intervals. 3 [128] and 4 [50]. T@V _ and distance ran above 90 % of vV Omax during four different HIT sessions including long intervals. The and the development of a V _ time needed to reach V O2max during constant-speed exercise to exhaustion has received considerable debate in the past [104. References: 1 [21]. SSG small-sided games (handball). through the priming effect of an adequate warm-up and/or _ O2 kinetics [133. work intensities of C95 % _ O2max are therefore recommended for maximizing v/pV _ O2max during single isolated runs. likely due to the high anaerobic energy contribution this requires [150]. passive recovery is therefore recommended when the relief interval is less than 2–3 min in duration. relief intervals should last at least 3–4 min at a submaximal intensity [153] to allow the maintenance of high-exercise intensity during the following interval. 76 % and 70 % vV .1. 134]. 3. 2-. respectively).1.and 6-min intervals.e.g. in national level runners _ O2max = mean ± SD 19. but longer intervals) and the exercise mode. its effects on performance capacity (time to exhaustion).e. when the possible ‘wash out’ effects overcome that of the likely reduced PCr resynthesis). 135. 137]. we would therefore recommend using fixed intervals durations C2–3 min that could be further adjusted in accordance with the athlete’s training status (with the less trained performing lower training loads. Additionally. there is no link _ O2max and time to between the time needed to reach V exhaustion [135. _ O2max) is reached 146]. while a beneficial performance effect on subsequent intervals can be expected with long recovery periods (C3 min [134. Additionally. If the time time needed to reach V _ needed to reach V O2max cannot be determined (as is often the case in the field). V O2max should then be reached from within 1 min 20 s to 2 min 20 s (at least when intervals are repeated). _ O2max has been using 50–70 % of time to exhaustion at vV suggested by the scientific community as an alternative to individualizing interval training [3. 83 %. prescribing training based on time to exhaustion is very rare compared with how endurance athletes actually train. 154].4 below with respect to uphill running).g. 14. especially for non- .1. However. PCr resynthesis. where V _ O2max (vV values were reached during 2-min work/2-min rest intervals. the time required to reach _ O2max has frequently been reported to be longer than V 75 % of time to exhaustion in some participants [131. peak V _ O2 was only ners (vV _ 82 ± 5 % of V O2max during 1-min intervals.1 ± 1 km/h). these latter sessions were performed at submaximal self-selected _ O2max for 1velocities (i. 91 %. neither blood [156. In practice. and that a steady-state (C95 % V _ after exercise onset within &4 s. impair PCr resynthesis (O2 competition) and trigger anaerobic system engagement during the following effort [160]. 163]. If an active recovery is chosen for the above-mentioned reasons (i. 148–150]. 162]. The current understanding is that active recovery can lower muscle oxygenation [158. active recovery performed during this period may negate subsequent interval performance using both long periods at high intensities ([45 % _ O2max) [153] and short periods of varying intensity v/pV [159. H? ion buffering. it appears more logical to use the time needed T@V _ O2max to individualize interval length [135] (e. Therefore. which has little to do with muscle lactate concentration [155].e. since a given percentage of time to exhaustion results in very different amounts of _ O2max. 5. 3. 4. which is only a moderately reliable measure (CV = 12 % [68] to 25 % [93]). and hence. In the context of long interval HIT. First. in the study by Seiler and Sjursen [71] in well trained run_ O2max = 19. muscle lactate oxidation) and. but not during 1 min/1 min [22]. if we consider that the time constant of the primary phase of the _ O2 kinetics at exercise onset (s) in the severe intensity V domain is generally in the range of 20 s to 35 s [131. while it reached 92 ± 4 during 2-min intervals. Intervals lasting 70 % of time to exhaustion have also been reported as very difficult to perform. While performing active recovery between interval bouts is appeal_ O2max and in ing to accelerate the time needed to reach V turn. irrespective of training status and exercise mode. e. Although performed on an inclined treadmill (5 %). active recovery is psychologically difficult to apply for the majority of athletes. 157] nor muscle [155] lactate has a direct (nor linear) relationship with performance capacity. to reach V _ O2max ? 1 or 2 min). These two variables must be considered in light of (1) maximizing work capacity during subsequent intervals (by increasing blood flow to accelerate muscle metabolic recovery. 140. 14]. regulation of inorganic phosphate (Pi) concentration and K? transport. is exhaustive by nature _ O2max and highly dependent on the accuracy of the vV determination [103]. Second. Finally. extending the work duration did not modify these peak values (93 ± 5 and 92 ± 3 % for 4.).3 Relief Interval Characteristics during Long-Interval High-Intensity Interval Training (HIT) When programming HIT.7 ± 1 km/h). 159]. _ O2max are not straightforward. time to exhaustion at vV _ O2max must addition to vV be determined. Additionally. 136]. 161. [3. proportion of time to exhaustion needed to reach V this is not a practical method to apply in the field. _ O2 to reduce the time (2) maintaining a minimal level of V _ needed to reach V O2max during subsequent intervals (i. The benefit of active T@V recovery has often been assessed via changes in blood lactate concentration [153. Indeed. induce a higher fractional contribution of aerobic metabolism to total energy turnover [134]. For athletes presenting with exceptionally long time to exhaustion. This is consistent with the data shown by Vuorimaa et al. 137. which _ O2max was not reached [130] (see probably explains why V Sect. respectively [71]).Author's personal copy HIT Programming: Cardiopulmonary Emphasis 323 As an alternative to using fixed long-interval durations.and 6-min intervals. both the duration and intensity of the relief interval are important [152]. starting from an elevated ‘baseline’) [3. Similarly. in _ O2max. repeating sets of 60 % of time to exhaustion is typically not attainable [137].1. to our knowledge. while the rationale of this approach is sound (50–70 % is the average _ O2max). 128] at V dences suggest that elite athletes tend to accumulate greater _ O2max per session at some point of the season.700 m [127]).250 m [69]. 4 9 6 min or 4 9 & 1. accelerated V Finally. When moderately trained runners _ O2max = 17. the subsequently larger motor units recruited and the greater reliance on concentric _ O2 contractions. 167]. Anecdotal evito 4–10 min [95 % [127. More research is required. 171] have shown that. 90 s). 3.9 ± 0. [175] the differences observed by Gajer et al. P. but active recoveries \ 50 % vV _ O2max in senior Demarie et al. Despite the expected higher muscle force requirement during hill running [173]. While V _ O2 reached 99 % vV _ O2max during the hill and track sessions. The present understanding of the determinants of HR recovery suggest. enabled athletes to spend a relatively high _ O2max (43 %) [21]. 102 % [174]). they chose a walking recovery mode of about 2 min [69]. proportion of the session at [90 % of V This particular high ‘efficiency’ was also likely related to both the young age [222] and the training status [141] of the runners (since both are generally associated with _ O2 kinetics).1.000–1. Fig. The reason for the lower T@V the hill HIT is unclear. extending passive recovery to 4 min did not provide further benefits with respect to running speeds. Gajer et al.3 km/h). the cardiorespiratory responses to field-based HIT sessions involving uphill or staircase running has received little attention. More long-distance runners (vV recently.000 m [21]). recreationally trained cyclists (V .Author's personal copy 324 M. but rather to the magnitude of the central command and metaboreflex stimulations [168]. Buchheit et al.1.6 ± 0.300– 1. in highly trained young _ O2max = 18. With intervals performed successively (no passive pauses. During recovery.5 Volume of HIT with Long Intervals Another _ O2max is the variable that can be used to maximize T@V number of long-interval repetitions. B. 6) in well trained triathletes (vV V 19. If we consider that running uphill at 85 % vV with a grade of 5 % has likely the same (theoretical) energy requirement as level running (or treadmill running with a 1 % grade to compensate for wind resistance [105]) at & 105 %.000–1. could have been even greater if the flat condition was ran at a faster (and possibly better matched) speed (105 % vs. As well. HR is neither related to systemic O2 demand nor muscular energy turnover [142. 166]. 128] _ O2max. the return of HR to a fixed value or percentage of HRmax is sometime used in the field and in the scientific literature [165. probably due to the increased forces needed to move against gravity. It is worth noting. in an attempt to individualize between-run recovery duration. in practice. for a given running speed. the T@V ‘moderately’ lower during the hill HIT (27 % vs. _ O2max/total exercise time ratio shown The low T@V by Millet et al. all of which are believed initiators of the V slow component [172]. despite a passive recovery intensity (walk). Laboratory studies in trained runners (VInc. 3. however. 16 min (4 9 4 min or 4 9 &1. athletes generally run slower on hills versus the track [173]. Laursen endurance athletes.6 km/h) were asked to self-select the nat(vV ure of their relief intervals during an HIT session _ O2max on a treadmill with (6 9 4 min running at 85 % vV 5 % incline). [128] (34 % when considering time [90 % _ O2max = _ O2max. intervals in these sessions might not have been long enough to observe the additional slow component generally witnessed with uphill running (& 2 min [172]). [174] found in elite French middle-distance runners _ O2max = _ O2max = mean ± SD 21. [127] reported a longer T@V _ O2max = 16. V (vV _ 78 ± 4 ml/min/kg) that T@V O2max observed during a hill HIT session (6 9 500 m [1 min 40 s] 4–5 % slope [85 % _ O2max]/1 min 40 s [0 %]) was lower compared with a vV ‘reference’ track session (6–600 m [1 min 40 s] {102 % _ O2max}/1 min 40 s [0 %]).1. this is unlikely enough to compensate for the reduction in absolute running _ O2max speed. Compared with 1-min recovery intervals. 24 min (6 9 4 min or 6 9 &1.1 km/h). to clarify the cardiorespiratory responses to uphill running at higher gradients ([ 10 %) or to staircase running that may _ O2 values due to participation of upper require very high V body limbs (back muscles and arms when pushing down or grabbing handrails). nevertheless.e. however.1.9 km/h) was likely related to the introduction of 5-min passive pauses every second interval. depending on the HIT format. which enabled athletes to accumulate. 15 min (5 9 3 min or 5 9 &800–1. _ O2max during ES & .6 ± 1. However.500 m [71]) and 30 min (6 9 5 min or 5 9 &1. that very few authors have examined HIT sessions/programmes that are consistent with the sessions that athletes actually perform. that this practice is not very relevant [69].Test C 20 km/h) _ O2 [170. no blocks _ O2max between runs). the 2min recovery duration enabled runners to maintain higher running speeds. showed. Buchheit.1.2 ± 0. that even shorter runners (vV recovery periods (i. from 10 min [90 % [21. and that research on the optimal _ O2max per session is limited.0).250 m [46]). In T@V _ O2max: *52 ml/min/kg). V is higher during uphill compared with level running after a couple of minutes. Cumulated highT@V _ O2max) exercise time during typical intensity ([90 % v/pV sessions in well trained athletes has been reported to be 12 min (6 9 2 min or 6 9 &600 m [128]). 44 %.4 Uphill Running during HIT with Long Intervals Despite its common practice [169]. and 105 % V _ O2max/exercise time ratio was respectively.6 km/h. 91. However. despite ‘very large’ and ‘moderate’ reduc_ O2max tions in time to exhaustion (ES = -4. to maintain an average intensity (60–80 % of vV HIT intensity of 85 %) might partially have influenced the _ O2 responses. [177] compared with Thevenet et al’s. 3.1 Effect of Work Interval Intensity on _ 2max Billat et al. the first approach to maximizing _ O2max during such sessions should be to focus on the T@V most effective adjustments to work/relief intervals (intensity and duration) that increase time to exhaustion.7). [8 min [43. hence. 95.2 Effect of Work Interval Duration on T@VO _ O2 The effect of work interval duration on systemic V responses during HIT involving repeated short intervals was one of the first parameters examined in the HIT literature [11.8 km/h). _ 2 Responses to HIT with Short Intervals 3. In practice. 0. runs were not performed to exhaustion. Similarly. see Part II). they prescribe a series or set of HIT [50. T@V _ O2max in relation to T@V the total duration of the HIT session.61. there is little data available on repeated efforts lasting less than 15 s. study [179] (ES: ?1. selection of a work bout intensity that ranges between _ O2max ([89 % and 105 % of VIFT) 100 % and 120 % of vV may be optimal. instead of vV appears that during HIT that involves short work intervals. since increasing exercise intensity has other implications (e. while the ([102/120 % VIFT/vV _ O2max/exercise time ratio is high (81 % and 77 % at T@V _ O2max. 7a. T@V largely correlated with total exercise time (i.2 VO _ O2max is For short interval HIT runs to exhaustion. Further research examining the influence of these particular sessions in more highly trained athletes are. _ O2 with the increase in individual improvements in T@V work intensity were inversely correlated with the athletes’ _ O2 kinetics at exercise onset primary time constant for V (r = 0.8) ment in the T@V [117]. [23] were the first to show the T@VO _ O2max during HIT with effect of exercise intensity on T@V short intervals (15 s/15 s) in a group of senior (average age: _ O2max = 15. 179]). 4 9 4 min) [176]. _ 2max 3. It is therefore possible that if the runs at 100 % had been performed to exhaustion [177]. Surprisingly. the use of repeated at 120 % vV sets of such training can allow the accumulation of a suf_ O2max.4) and T@V (ES = -0. higher neuromuscular load. 4 9 8 min = 32 min at 90 % HRmax) may be more effective than more traditional HIT sessions (e. 52 years) distance runners (vV While the concurrent manipulation of the relief interval _ O2max. greater anaerobic energy contribution.e.e.6). How_ O2max/exercise time ratio (85 %) was not ever. showed that larger volumes of HIT performed at a lower intensity (i. To conclude. 90 % CI 0. it VIFT. Hence. Interestingly. 180]. In this context. 178]. [177].93 km/h) was associated with a (vV _ O2max/exercise time ratio ‘large’ improvement in the T@V (ES = ?1.g. The twofold magnitude difference in Millet et al.e. 50. Nevertheless. in the study by Millet et al. well trained athletes are ficient T@V generally able to perform HIT at this intensity for longer periods (i. respectively [179]. required to confirm these findings. 5 min 47 s _ O2max [117]).7 ± 1. it is important to consider the strategies _ O2max within a given time period.Author's personal copy HIT Programming: Cardiopulmonary Emphasis 325 Seiler et al. however.5). such programming manipulations need to use a cost/benefit approach. Practically speaking.9 ± 1. total T@V for a given HIT series is usually low [117] (i.2. 128.6) is likely due to the fact that Millet et al’s. this data implies that coaches should programme HIT at slightly greater exercise intensities for athletes presenting _ O2 kinetics (i.7 ± 0.e. older/less trained [141]). 12]. 68 %. but implemented with pre-determined sets.1.2 vs.98). is used [94]). increasing work intensity from 100 % to 110 % of _ O2max during a 30 s/30 s format in trained young runvV _ O2max = 17. especially when _ O2max.1. respectively). 177.e. needed to maximize T@V or to define ‘time-efficient’ HIT formats with respect to the _ O2max/exercise time ratio (i. however.3 km/h) lead to a ‘large’ improve(vV _ O2max/exercise time ratio (ES = ?1. 177. 177]. the authors did show that increasing work V _ O2max was interval intensity from 90 % to 100 % of vV _ O2max/ associated with a ‘small’ improvement in the T@V exercise time ratio (81 % vs.9 km/h) induced a ‘moderate’ ners (vV _ O2max/exercise time ratio increase in the T@V (ES = ? 0. despite the .8 ± 0. warm-up excluded). coaches do not prescribe HIT sessions to exhaustion. or for with slow V athletes exercising on a bike [140]. time to exhaustion) [14]. suggesting that the time constant could be an important variable to consider when selecting HIT variables [116.g. Using a compared with 100 % of vV fixed relief interval intensity (Fig.2) [177]. ES = ? 0. the T@V substantially greater using a work interval fixed at 110 _ O2max (ES = ?0. increasing the ence in T@V _ O2max during a work intensity from 110 % to 120 % of vV 15 s/15 s format in physical education students _ O2max = 16. ?0. exercise 130 % and 140 % of vV _ O2max capacity is typically impaired and. [117.2.1.e. this would have compensated for the lower efficiency of the protocol and decreased the differ_ O2max observed. A slight increase in work _ O2max during a intensity from 100 % to 105 % of vV 30 s/30 s HIT format in well trained triathletes _ O2max = 19.2). Additionally. With respect to the use of very-high-exercise intensities _ O2max) for HIT. [185] a further increase in the interval duration _ O2max to 5. _ 2max. exhaustion and T@V Compared with passive recovery. Simithe T@V _ O2max = 16. as a function of changes in work interval intensity (a: references 1 [117].1(2) 84(10)% [La]: 12. 7 Mean ± SD total time and T@V of HIT.9 km/h) induced ‘very large’ increases in _ O2max (9 vs.3 Characteristics of the Relief Interval and _ 2max The intensity of the relief interval also plays a T@VO _ O2 response during HIT involving short major role in the V _ O2 during the intervals. with more than 50 % of the O2 used derived from oxymyoglobin stores [11]. Mean ± SD mean ± SD T@V [La] mmol/L is provided when available (values for study 6 [186] were all \ 6 mmol/L and are therefore not provided). 186]). [164.e.1 km/h).5 min (ES = 0. 34 min.3(2) 0% [La]: 11. the cardiopulmonary responses of such efforts are relatively low [183]. VO _ O2max. Buchheit. 5 [185] and 6 [186]) and relief interval intensity (c: references: 7 [190].indicates the variable that was manipulated. Considering the importance of V _ O2max [177].4).5 min. increaslarly. During the recovery periods.6(2) 68(19)% [La]: 8.2. intensity interval training.Author's personal copy 326 M. also increases T@V (Fig. extending work interval duration from 30 s to 60 s using a fixed-relief _ O2max = duration of 30 s in well trained triathletes (vV 19.5(3) 77(53)% 23(18)% [La]: 14.7(5) 81(48)% 15s[--%]/15s[0] 1 30s[--%]/30s[50% vVO2max] 3 30s[--%]/30s[50% vVO2max] 2 b 65 60 55 50 45 40 35 30 25 20 15 10 5 0 15s 20s 25s 30s 60s 7(7)% 32(11)% 1(1)% 2(1)% 6(4)% T@%VO2max (90%) T@%VO2 max (95%) 1(1)% 50(18)% [La]: 12. 30 s/30 s vs. 8 [188] and 9 [164]). change in _ O2max/exercise ratio. ES = ?2. Percentages refer to the _ O2max relative to total session time. work intervals C10 s appears to be required _ O2 responses.9.g. runs to exhaustion Time (min) Time (s) . indirectly time to _ O2max. * indicates _ 2max minimal running speed associated with VO vVO HIT not performed to exhaustion common approach used by coaches (e. the to 60 s extended T@V _ O2 30-s condition). ES = ? 2. [128.7(2) 42(17)% [La]: 11. hence. 3. work interval duration (b: references 4 [128]. oxymyoglobin stores are rapidly restored and then available for the following interval [11].7(2) 63(26)% [La]: 9. 185.0(3) 32(22)% * 46(20)% [La]: 13. these data suggest kinetics for extending T@V that longer work intervals (e. During very short runs (\10 s). while keeping _ O2max work relief intervals constant. HIT high_ 2max maximal oxygen uptake. 187.4) and/or relief intervals are short/intense enough so that they limit complete myoglobin resaturation. What is known of course is that prolonging exercise duration increases the relative aerobic energy requirements [184].9).5(2) 2(2)% 7(5)% [La]: 7.1.1. Therefore.9 ± 0.5(2) 31(22)% --s[100% vVO2max]/30s[50]% 4 --s[105% vVO2max]/20s[0] 6 --s[115% vVO2max]/20s[0] 6 T@ VO2max (90%) [La]: 6(2) 24(19)% --s[100% vVO2max]/15s[50%] 5 c 50 40 0% vVO2max 50% vVO 2max /41% VIFT 67% vVO2max /56% VIFT 84% vVO2max /71% VIFT 30 20 10 0 [La]: 10. ‘very large’ increase in T@V ES = 2. As a result.g. or for exercising on a bike [140]. Fig. -.2(1) 23(10)% 105% vVO2 max /89% V IFT 110% vVO2 max /94% VIFT 120% vVO2 max /102% VIFT 130% vVO2 max /111% VIFT Time (min) 20 15 10 5 0 [La]: 11. 0 min. Laursen 30 25 a T@VO 2max (90%) 100% vVO2max /85% VIFT [La]: 8. 182]. using a fixed work/rest ratio in the same group of subjects. in the context of _ O2max or 89/ HIT involving short intervals (100–120 % vV 105 % VIFT).8(2) 77(12)% 15s[120% vVO2max]/15s[--]% 7 30s[105% vVO2max]/30s[--]% 8–9 _ O2max during different forms Fig. 15 s/15 s) are _ O2 kinetics (i. in wrestlers (vV ing running work interval duration from 15 s to 30 s lead to _ O2max (4 vs. unless exercise intensity is set at a very high level (as detailed in Sect. a 15 s/15 s HIT _ O2max/exercise time ratio session enables a greater T@V than a 30 s/30 s session is unknown. 10 s/10 s.8) [128].3 ± 1. including short intervals.1(4) 93(23)% [La]: 13. 1. ATP requirements in working muscle are met predominantly by oxidative phosphorylation. 3. the specific to elicit high V effect of work interval duration. older/ preferred for individuals with slow V less trained [141]). 188]). despite a shorter T@V total session time (28 vs. Surprisingly. has not been investigated thus far. 10 s/ 20 s) [181. B. 7c. For example. 2 [179] and 3 [177]).5 vs. 7b. Increasing the work interval duration. ES = -0. whether. P. for example. VIFT running _ 2max time spent at 90 % or 95 % of V T@VO speed reached at the end of the 30–15 Intermittent Fitness Test. since it affects both the actual V sets and exercise capacity (and.1(3) 55(20)% 140% vVO2 max /120% VIFT [La]: 11. performing 4-min recoveries (30 s rest. 30 s rest) every 6 repetitions (30 s/30 s) 50 % vV _ O2max was associated with a ‘moderately’ lower T@V (ES = -0.1. Not surprisingly. this is likely why HIT sessions to exhaustion are not often practiced by athletes. 188]. all ES between the different work/relief ratios examined were ‘small’ to ‘very _ O2max might large’.7 ± in endurance-trained young runners (vV 0.3). the _ O2max might not differ between active and absolute T@V passive recovery conditions [190] (ES = -0. irrereturn to high V spective of the active recovery used. these studies suggest that. In general. A lower volume (shorter series or less sets) may be used for other sports (i. 177. a _ O2max of 5–7 min is likely sufficient [116]) and/or for T@V maintenance during unloading or recovery periods in an endurance athlete’s programme. The time needed to reach V during different work. athletes should expect to exer_ O2max]/ cise for a total of 30 min using a 30 s [110 % vV _ O2max] format.and/or relief-interval intensities (i. this would likely be challenging. the number of intervals programmed should be related to the goals of the session (total ‘load’ or total _ O2max expected). Therefore. HIT sessions such as 2 9 (12–15 9 15 s [120 % VInc. and/or performing active recovery during longer-relief interval durations (C20 s).1. since the T@V _ O2max/total 30 s [50 % vV exercise time ratio is approximately 30 % (Fig.4). 179. or using longer work intervals and/or shorter relief intervals. respectively) [164. as well as to the time needed to T@V _ O2max and the estimated T@V _ O2max/exercise time reach V _ O2max ratio of the session. these studies showed shorter time needed to _ O2max values for work intensities C105 % vV _ O2max reach V _ and relief intensities C60 % vV O2max. but the _ O2max/exercise time ratio is substantially greater T@V when active recovery is implemented (ES = ?0. 188]. 179.and relief-interval intensities involving short HIT (30 s/30 s) was recently examined in young endurance-trained athletes [164. when considering runs to exhaustion during 15 s/15 s exercises. relief interval _ O2max should be recomintensities around &70 % vV _ O2max and the T@V _ O2max/ mended to increase both T@V exercise time ratio [23]. 179]. Taken together. The fact that active recovery had a _ O2max during the 30 s/30 s likely greater impact on T@V [164.Author's personal copy HIT Programming: Cardiopulmonary Emphasis 327 involving active recovery are consistently reported to be 40–80 % shorter [164.e.6). _ O2max of &10 min per If we consider that a goal T@V session is appropriate to elicit important cardiopulmonary adaptations (Sect. For example. 188] compared with the 15 s/15 s [190] exercise _ O2 reaches lower values model is related to the fact that V _ O2 during 30 s of passive rest. for both coaches and athletes alike. This is likely related to the time athletes needed to _ O2 levels after each recovery period. Increasing the recovery intensity to 84 % _ O2max (ES = -0. In practice. Buchheit M. .4 Series Duration. unpublished data). and might enable players to spend &7 min _ O2max (considering a T@V _ O2max/exercise time ratio of at V 35 %. for the short HIT formats examined thus far.e. In elite handball.1. but reduced ‘moderately’ T@V _ O2max/exercise time ratio increased ‘very largely’ the T@V (ES = ?3. time needed to reach V be accelerated by manipulating HIT variables during the first repetitions of the session. for example. During a 30 s/30 s exercise model. a factor of obvious importance when implementing predetermined sets of HIT [50. 187–190].3).2. the characteristic of the relief interval intensity can be adjusted in alignment with the work intensity. in team sports. using more intense workand/or relief-interval intensities during the first two to three intervals.1. 3 min at _ O2max.4 and ?0. 188]. 128. Conversely. Despite a lack of statistical differences [164. 178]. While it could be advised to consistently recommend HIT runs to exhaustion _ O2max. recovery _ O2max were associated intensities of 50 % and 67 % of vV _ O2max with ‘small’ and ‘very large’ improvements in T@V _ O2max/ (ES = ?0. 2 9 (20 9 10 s [110 % VIFT]/20 s [0]) is common practice. compared with passive recovery. In football (soccer). _ 2max Dividing 3. to optimize T@V psychologically speaking. 178].3 km/h). we recommend programming passive recovery B15–20 s for non-endurance sport athletes not familiar with performing active recovery.3 and ?4. respectively) and the T@V exercise time ratio (ES = ?2. which directly affects V levels during the following effort. Since it is unrealistic to perform a single 30-min session. Sets and T@VO HIT sessions into sets has consistently been shown to _ O2max [50. 7a). For this reason. which corresponds to _ O2max (14 min with a T@V _ O2max/exercise &6 min at V time ratio of &45 % [190]). i.1.e. _ O2max) the runners neework: 100 % and relief: 50 % vV _ ded more than 7 min to reach V O2max. and lower-relief exercise intensities used for higherwork interval intensities and durations [117. with higher-relief interval intensities used for lower-work interval intensities [23]. it is possible for it to be broken into three sets of 10–12 min (adding 1–2 min per set to compensate for the time needed _ O2max during the second and third set).Test]/ 15 s [0]) are often implemented [95]. In the field then.5). 3.8) despite ‘very large’ increases in time to _ O2max/exercise time exhaustion (ES = ?4. using slightly lower work. the T@V ratio was therefore ‘very largely’ reduced (ES = -2.3) [178].9). reduce the total T@V _ O2max = 17. 128. Such a to regain V session is typical to that used regularly by elite distance runners in the field. [198] showed that V _ 87 % V O2max) during repeated 30 s cycling efforts (200 % _ O2max and therefore not actually ‘all-out’) interof pV spersed by 2-min passive recovery.4 VO Compared with the extensive data available on cardiorespiratory responses to long and short HIT. [13] demonstrated that RSS were aerobically demanding (i. 193.61. P. Similarly. 196. with two subjects showing no _ O2max) [142]. except for Dupont et al’s. it was observed that six (45 %) of _ O2max on four occasions. however. Nevertheless. Tabata _ O2max was not reached (peak of et al.3 Short versus Long Intervals and T@VO A direct comparison between long and short HIT sessions. we have reanalysed data from previous studies [30. For the purpose of the present review. there was a _ O2max and both V _ O2max negative correlation between T@V _ O2 kinetics at (r = -0. with respect to T@V using RSS may be questionable to apply in some athletes. _ O2max 90 % CL -0. when considering the four different forms of RSS performed by the same group of 13 athletes [193. however.2 ± 0.e. V of the entire RSS duration (i. study [192]). These important individual V responses to SIT sessions were partly explained by variations in cardiorespiratory fitness (i.84. 8. ran in &1 min 40 s) and 10 repetitions of a 30 s/30 s HIT session (work/relief intensity: 105/50 % _ O2max) in elite middle-distance runners (vV _ O2max = vV _ _ O2max 21. In addition.e. four (31 %) on two.20) and V . the majority of athletes may _ O2max during the repeated sprints. spend up to 2–3 min at V _ O2max during an RSS. It is worth noting.19). -0. Gajer et al. no relationship between the number of times that _ O2max and V _ O2 kinetics at _ O2max was reached or the T@V V exercise onset. 8. most subjects reached values close to (or above) 90 % of their _ O2max and HR. _ O2max values for several 158. 30. V however. 2 _ O2max is often reached and sustained for 10–40 % [35]). (ES = ?2.8) [128].1. 0. 30. 194]. T@V has not been reported. lower panel [13. _ O2max. Nevertheless. 17 s).5 VO The important research showing the benefits of SIT [126]. While V O2 reached 105 % V _ O2max was not actually attained during the track session. _ O2max. When manipulating key variables already described (Fig.1. _ O2max). with two (15 %) never reaching _ O2max during any of the RSS. Similarly. There was.6 km/h). 10–60 s. as measured during submaximal exercise _ O2max. Dupont et al. Laursen _ 2max 3. -0. T@V Long intervals were however ‘moderately’ less ‘efficient’ _ O2max/exercise time than a 60 s/30 s effort model (T@V ratio. these data suggest that long intervals and/or short intervals with a work/ relief ratio [1 should be preferred due to the greater _ O2max/exercise time ratio. ES = -0.6). as is often done in practice [180. 197]. T@V during the 30 s/30 s intervals (10 %. to date. 192–195]). 102 % T@V _ vV O2max. with very short passive recovery periods _ O2max by repeating 3 s (i. the number of times that V _ was reached was inversely related to V O2max (r = -0. _ 2 Responses to Sprint Interval Sessions 3. few data available showing the acute physiological responses to typical SIT sessions that might be implemented in practice. we recently showed [142] that during a ‘true’ all-out SIT session. T@V _ O2max was only 22 s V on average (range 0–60 s. More precisely. notwithstanding. In contrast. 158. since these may increase systemic O2 demand without the need for increasing sprint distance. and/or changes in direction [194]. the total T@V over the four different RSS was inversely correlated with _ O2max (r = -0. are also of interest. To our knowledge. T@V _ 2 Responses to Repeated-Sprint Sequences 3. Buchheit. 90 % CL -0. An RSS is generally defined as the repetition of [two short (B10 s) all-out sprints interspersed with a short recovery period (\60 s) [191].55. a number of players did not reach V _ O2max showed high interindividual variations and T@V (CV = 30–100 %). upper panel [13. [144].68. If RSS are repeated two to three times per session. especially those of high fitness. relatively little has been presented on the acute responses to RSS. has only been reported twice in with respect to T@V highly-trained athletes. and V _ O2max was reached by values [90 % V _ O2 five (50 %) subjects only. When the data from the V _ O2max four RSS were pooled. have shown [65 % V _ O2max during repeated sprinting that footballers can reach V _ O2max during RSS [192]. If the track session is con_ O2max/exercise sidered as the ‘reference’ session (T@V _ O2max was ‘very largely’ lower time ratio: 44 %). The introduction of jumps following the sprints [193].Author's personal copy 328 M.00).85. 8 a). it appears that To increase T@V sprints/efforts should last at least 4 s. Early in the 1990s. V during the 30 s/30 s session. that during all RSS examined here (Fig. B.90. 90 % CL -0. which could increase muscular load and/or injury risk (see review Part II).1. 192–195]). there is. some athletes can reach V sprints only (15 m). These data show that. Fig. Balsom et al. [174] compared _ O2max between 6 9 600 m (track session. Taken together. 158. [128] showed that performing 2 min/ 2 min intervals enabled triathletes to attain a ‘very largely’ _ O2max compared with a 30 s/30 s session longer T@V _ O2max/exercise time ratio = ?2.2. 194] to provide T@V forms of RSS (Fig.2). 8. Millet et al. and that the recovery should be active and less than 20 s (Fig.e. ES & -2. one (8 %) on them reached V three.e. however. we have highlighted the V responses to various forms of HIT. there was no link between T@V _ and V O2 kinetics at exercise onset.e. RSS and SIT sessions allow for a limited T@V _ T@V O2max compared with HIT that involve long and short intervals.e. data from high-level athletes [128. When available. 15 m) with of V passive recovery when sprints are interspersed with very short pauses (i.e. 200]. 202]. As with RSS. is still debated v/pV [205–207]. Along these same lines. It has been shown that there is a progressive shift in energy metabolism during a SIT session. respectively. Since reaching and maintaining an elevated cardiac filling is believed to be necessary for improving maximal cardiac function [58. 3. 8 a Mean ± SD V sequences.6 Summary _ O2 In this section of the review. [percentage]) is _ O2max. vVO2max minimal running speed required to elicit _ O2. COD changes of direction.20. is still to be determined. T@V sole criteria of importance for examining when assessing the cardiopulmonary response of a given HIT session. The dashed lines represent the shorter sprint and recovery durations likely needed to achieve at least 80 % of _ O2max. especially as the number of sprint repetitions increase. VO _ _ maximal V O2. SV behaviour during an incremental test is VO2 (% VO 2max) 120 Recovery time (Log [s]) 60 40 30 20 VO2 >50%VO2max VO2 >55%VO2max VO2 >65%VO2max VO2 >75%VO2max VO2 >80%VO2max VO2 >85%VO2max Wdw +Jump 90COD +Jump 10 0 1 2 3 4 5 6 7 Sprint duration (s) _ O2 responses during selected repeated-sprint Fig.g [25–27. with increasing sprint repetition number.90). VO and 7 [193]. 90 % CL 0. with a greater reliance on oxidative metabolism when sprints are repeated [199.5s[0%]) 2 6x (4s Wdw/21s[0%]) 3 15x (40m/24. The intensity of the relief interval (i. 17 s). 6 [30] _ 2max _ 2 oxygen uptake. 4 [194]. Wdw refers to sprints performed on a non-motorized maximal V treadmill (submaximal) exercise cessation (r = 0. 201. mean ± SD time spent above 90 % of V _ O2 responses during the repeated-sprint sequences b The mean V presented in section a are categorized into six colour-coded families _ O2max elicited) and then plotted as a function of (based in the % of V sprint and recovery duration. Finally. important between-athlete and reach V between-HIT format differences exist with respect to _ O2max. continuously). intermittently vs. Combined. muscle O2 demand likely is.4s[0%]) 2 20x (15m/17s[0%]) 6 6x (4s Wdw/21s[45%]) 3 _ O2 is not high during noting that although pulmonary V SIT. since this requires the continuous monitoring of SV during exercise (e. 3.Author's personal copy HIT Programming: Cardiopulmonary Emphasis 329 100% 41(14)% 100 90 69% 100% 15(13)% 35%* 50% 80 70 60 50 40 8(6)% 69% 53% 46% 19(27)% 9(10)% 29(25)% 6x (25m COD90+Jump/21s[45%]) 7 6x (25m COD90/21s[45%]) 4 6x (25m+Jump/21s[45%]) 7 15x (40m/120s[0%]) 1 15x (40m/25s[50%]) 5 6x (25m/21s[45%]) 4 15x (40m/60s[0%]) 1 15x (40m/30s[0%]) 1 40x (15m/27. can enable athletes to _ O2max. 204]).4s[0%]) 2 20x (30m/25. 174] suggest that long intervals and/or short intervals with _ O2max/ a work/relief ratio [1 should enable a greater T@V exercise time ratio during HIT sessions. whether SV is maximal at _ O2max. Defining this key intensity. or prior to their occurrences. References: 1 [13]. muscle deoxygenation levels and post-sprint reoxygenation rates have been shown to become lower and slower. However. 59. _ O2max 0. Interestingly. both the expressed as a fraction of the vV _ O2max (runner) and the percentage of participants that reached V _ O2max (clock) are provided. training at the intensity associated with maximal SV may be important [201]. 5 [192]. Circles indicate active recovery. when properly manipulated.68. it is worth .e. Note (see arrow) that 75 % V _ O2max can be achieved with very short sprints (i. as well as that involve varying quantities of T@V _ O2max the most efficient way of accumulating a given T@V in an HIT session (i. This response implies a greater O2 demand in the muscle with increasing sprint repetition (since O2 delivery is likely improved with exercise-induced hyperaemia) [142]. 2 [195].1. It appears that most HIT formats. The methods of _ O2max development and performaximizing long-term V mance adaptations using different forms of HIT sessions _ O2max. remains difficult.2 Cardiac Response with HIT and Repeated-Sprint Efforts Due to the varying temporal aspects [70] and possible _ O2 and cardiac output (Qc) during dissociation between V _ O2max might not be the intense exercise [201. 203].3 [158]. 6 L/min. 25.2. and despite contradictory claims [210]. In addition. using a rebreathing method in untrained men. ES = -2. In fact.2 ± 3. [3–4 min/ [2 min) might allow athletes to reach a high SV during the work (and possibly the relief intervals). ventricular filling partly depends on blood volume. France [213. Manaetec. Such a format would allow such athletes to maintain their peak SV for 24 9 20 s = 480 s. 15–30 s) with long recovery periods ([45 s) might also be effective at reaching high values both during exercise [215] and possibly. respectively). presence of a HR deflection at high intensities [208]). training status and various individual haemodynamic behaviours to different exercise modes. incremental vs. HRmax was nevertheless ‘very largely’ lower (149 ± 26 vs. repeated short supramaximal work intervals (e. and not during exercise. 9). i. 3 min at pV (30 % of the anaerobic power reserve.. In the only longitudinal study to date comparing the effect of short versus long HIT on maximal cardiovascular function in university _ O2max: 55–60 ml/min/kg) [59]. as well as methodological considerations in the measurement of SV may explain these differences [205–207]. which can. [215] also observed. In partial support of this. constant power vs. in the 1930s. 204] and &4 min [27]. ?0. [176] _ O2max: *52 ml/min/kg). as well as body position (more supine during rowing or swimming vs. constantpower bouts at high intensity.g. 214]). and while further analysis on a greater number of subjects is needed. 9).g.1]. _ O2max or repeated 15-s sprints incremental test. et al. training volume = 10 h/week) V showed its highest values consistently during the recovery periods (upright position on the bike). 94 ± 15 ml. In acquiring the answer to this question.g. intermittent. Fontana et al. i.g. 15/15.e. In these studies.9 ± 2. there was a students (V ‘small’ trend for greater improvement in Qcmax for the long interval protocol (ES = ?1 vs. individual training background and particular haemodynamic behaviours (e. P. To conclude. Although these results were obtained during supine exercise in untrained patients. one needs to take into account individual characteristics. Surceding submaximal cycling exercise (60 % V prisingly. As discussed in Sect. is still unknown. and then decreased [24. continuous vs. although this is not always the case [207]. more upright during running and cycling). Laursen likely protocol-dependent [202] and affected by training status (e. 2. HIT sessions might trigger cardiocirculatory adaptation via cardiovascular adjustments occurring specifically during the recovery periods. It is worth noting that Seiler et al. HIT sessions. showed.e. ‘largely’ greater SV values at the end of a 30 s all-out sprint compared with an incremental test to exhaustion (127 ± 37 vs.Author's personal copy 330 M. _ O2max = 69 ml/min/kg. they contributed to the widespread belief that the repeated recovery periods and their associated high SV accounted for the effectiveness of HIT on cardiocirculatory function [211]. the nature of exercise.3). which tends to be higher in trained athletes) [206]. on the basis of the limited data available.3 vs. Along these same _ O2max appear to be lines. the optimal nature and intensity of exercise needed to produce the greatest SV adaptations is not known. While we acknowledge the limitations inherent to the impedance method used (PhysioFlow. 190 ± 12 beats/min. Inconsistencies in exercise intensities.2). Alternatively. Cumming reported. alternating work and rest periods during HIT with short intervals might also induce variations in the action of the venous muscle pump. so there was no substantial difference in maximal cardiac output (Qcmax) [18. 216]).] &2 min [24. such as fitness level. might also affect the SV reached and maintained throughout the exercise bout. which is similar to what can be sustained during a constantpower exercise performed to exhaustion [25]. Irrespective of the exercise. or whether achieving a certain quantity of time at Qcmax (T@Qcmax) is needed to maximize its adaptation. intermittent). in 1972. We recently collected haemodynamic data in well trained cyclists that partly confirmed Cumming’s findings (Buchheit M. that maximal SV values were reached during the exercise recovery period. in recreational cyclists (V that accumulating 32 min of work at 90 % HRmax may . However. 27] prior to fatigue. Buchheit. 26. including near-to-maximal long intervals with long recovery durations (e. irrespective of the exercise intensity [209]. ES = -0. there is limited data on cardiac function during exercises resembling those prescribed during field-based HIT sessions. it might be recommended to prescribe a variety of different training methods to gain the adaptation advantages of each exercise format. i. Following the beliefs of German coach. SV reached maximal values within &1 min [26].g [46. Interestingly.7 for 4 9 4 min vs. 204] or remained stable [25. Takahashi et al. Fig.e. in turn. [212] also reported in untrained males that during the first 80 s of an active recovery (20 % _ O2max). 17. Take for example an HIT session involving three sets of eight repetitions of a 15 s sprint (30 % APR) interspersed with 45 s of passive recovery (long enough for peak SV to be reached). unpublished data. Woldemar Gerschler.and short-interval sessions (i. the SV of a well trained cyclist (peak power output = 450 W. APR). ES = ? 1.e. B. whether Qcmax adaptations are comparable following long. 4-min intervals &90–95 % v/pV receiving the greatest interest to improve cardiopulmonary function (e. these particular and still hypothetical changes in SV during recovery had never before been examined during typical HIT sessions in athletes. limit the maintenance of a high SV [60]. in recovery (Fig. SV values were 10 % greater than during a preV _ O2max). these preliminary data lend support to the belief that despite its supramaximal nature. 59. In a practical way. 45. and. p VO _ 2max minimal power associated VO _ O2max. SV and muscle oxygenation (TSI) during an Fig. and (c) the early phase of an HIT followed by 3 min at pV session (i. In this latter case [176]. In contrast. ES = ?0. APR anaerobic power reserve. the different aspects of HIT pro_ O2max gramming have been discussed with respect to T@V and cardiopulmonary function. compared with the ASR. 4 Conclusions In Part I of this review.98. TSI tissue saturation index with V . maximal SV values are consistently observed during the post-exercise periods. To individualize exercise intensity and target specific _ O2max and acute physiological responses (Fig. For run-based HIT sessions. 14 min ± 4 min. a greater adaptation. ES = ?1. if properly manipulated. but RSS and SIT sessions allow limited V _ O2max compared with HIT sessions involving long T@V _ O2 responses during RSS and SIT and short intervals.0) and. Finally. SV (ml) and muscle TSI (%) 180 160 140 120 100 80 60 40 0 500 1000 1500 2000 HR SV TSI 2500 Time (s) VO2 (ml/min/kg) b 200 180 160 140 120 100 80 60 40 0 80 VO2 60 40 20 0 HR (bpm). 90 % CL 0.99) [25]. For _ O2 responses instance. the following general recommendations can be made: 1. 0. HR. SV stroke volume. these results contrast with the idea that exercise intensity directly determines the training responses [59]. so that precise recommendations are difficult to offer. T@Qcmax (16 min ± 8 min vs. 90 % CL 0. HR heart rate. pacing strategies that can increase time to exhaustion but that sustain a high cardiorespiratory demand may also be of interest.Author's personal copy HIT Programming: Cardiopulmonary Emphasis 331 80 VO2 60 40 20 0 200 HR (bpm).79. is still unknown. respectively. supramaximal intermittent runs 200 HR (bpm).94. first four exercise bouts (15-s [35 % APR]/45 s [passive]. Based on the able to reach V current review. While SV was not measured. VIFT integrates between-effort recovery abilities and COD capacities that make VIFT especially relevant for programming short. maximal or supramaximal exercises. they show that both exercise intensity and accumulated duration of interval training may act in an integrated way to stimulate physiological adaptations in this population [176]. in turn. 0. b 5-min bout at 50 % of pV _ O2max. HIT high-intensity interval training. which is associated with a greater muscle deoxygenation during the incremental test. SV (ml) and muscle TSI (%) HR SV TSI 100 200 300 400 500 600 700 Time (s) VO2 (ml/min/kg) c VO2 80 60 40 20 0 VO2 (ml/min/kg) a actually induce greater adaptive gains than 16 min of work at *95 % HRmax [176]. the decrease in exercise intensity may have allowed for a greater T@Qcmax (or near Qcmax). adjusting work intensity based on V _ _ (constant-V O2 exercise at 77 % V O2max on average) instead of power (constant-power exercise at 87 % _ O2max) led to ‘moderate’ increases in time to exhaustion pV (20 min ± 10 min vs. Note the reductions in SV for intensities _ O2max during both the incremental and constant above [50 % of V power tests. _ 2max maximal oxygen uptake. 1).9) [25]. in turn. Rather. can enable athletes to reach _ O2max.93 to r 0. The V appear to be fitness-dependent. 15 min ± 5 min. since T@Qcmax has been shown to be largely correlated with time to exhaustion during severe exercise (r ranging from 0. Whether similar results would be observed in highly trained athletes who are more likely to require greater levels of exercise stress for further adaptations. Most HIT formats. with the fitter athletes less _ O2max during such training. v/pV ASR/APR or VIFT are likely the more accurate references needed to design HIT with long (C1–2 min) and short (B45 s) intervals. either following incremental. Important between-athlete and between-HIT format differences exist. SV (ml) and muscle TSI (%) 180 160 140 120 100 80 60 40 0 50 100 150 200 250 300 HR SV TSI 350 Time (s) _ O2. 9 a V incremental test followed by two sets of three supramaximal 15-s _ O2max immediately sprints (35 % APR). in a well trained cyclist.e. Billat LV.e. Understanding the physiological responses to technical/tactical training sessions is also likely an important aspect of successful training in team sport athletes. we recommend long. Especially in well trained athletes that perform exercises involving large muscle groups. 2012. Sports Med. b. Sportscience. as suggested for programming in the present review. Laursen PB. Laursen PB. P. and assuming the _ O2max may maximize the trainaccumulation of T@V ing stimulus to improving performance. Jenkins DG. as well as the influence that training status and cardiorespiratory fitness have on these responses.32:53–73. and long slow distance: the role of intensity and duration in endurance training. Vitoria˜ igo Mujika. Repeated-sprint ability—Part II: recommendations for training. as typically most studies are conducted with ‘fresh’ participants in controlled environments. how does one ‘‘best solve the . so that the optimal HIT sessions can be programmed as supplemental sessions (i. age and training status/ background. consideration for other important aspects of HIT programming. References 1. 2006. Acknowledgments No sources of funding were used to assist in the preparation of this review. 2001. 98. 41–50). Buchheit. 3. heat [217]).575:901–11. 2011. 2010. Sports Med. systems of play. ISBN 978-84-939970-0-7. 2. individual playing styles) [63. 8. Bangsbo J. B. Further research is also needed to improve our understanding of how to optimally manipulate HIT variables.and long-distance running. Part I: aerobic interval training. Intervals. environmental conditions (e. Total session volume should enable athletes to spend between &5 (team and racket sports) and _ O2max. the importance of continuous versus repeated ventricular filling at high rates for developing cardiovascular adaptations is not known. 2001. Further studies are also needed to examine the long-term adaptations to all forms of HIT/repeated all-out efforts presented in the present review with respect to gender. such as glycolytic anaerobic energy contribution. 3. 4. Girard O. 2010.and short-bout HIT with a work/relief ratio [1 (see Part II. Part II: anaerobic interval training.1:13–31. the implementation of HIT sessions should be individualized and considered using a cost-benefit approach.13:32–53. 220]. editor. 2): 11–23. thresholds.20(Suppl 2):1–10. in particular. Gibala MJ. Little JP.and long-distance running. since physiological and performance adaptations have been shown to occur in relation to the accumulated training load completed at high intensities [218]). 2009. _ O2max.31:75–90. while adding what is ‘missed’ during the technical/tactical sessions [151]. should also be considered. In: Mujika I. Interval training for performance: a scientific and empirical practice: special recommendations for middle. Additionally: There should be little delay between the warm-up and the start of the HIT session so that the time _ O2max is accelerated. 6.e. Tønnessen E. Gasteiz: In 7. while in practice. 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