We are grateful to Drs. Vollaard, Metcalfe, Kinghorn, Jung, and Little (hereafter Vollaard et al.) for taking an interest in our work and being willing to provide feedback. We are also grateful to the Editor of the Journal of Sport & Exercise Psychology (JSEP), Professor Martyn Standage, for offering us the opportunity and the space to share some thoughts that may help the readers of the journal gain a more balanced understanding of the issues at the core of this discussion. Admittedly, at first the issues raised by Vollaard et al. may seem strictly physiological and methodological in nature and therefore beyond the usual scope of JSEP. However, in this response, we try to explain to the readers of this journal, most of whom are students and academics with an interest in exercise and sport psychology, that the issues involved are not as esoteric as they might seem; they do have implications for the psychology of physical activity, as well as the broader field of exercise science.
We are heartened that Vollaard et al. found parts of our two papers (Ekkekakis et al., 2023a, 2023b) on the methodology of studies investigating affective and enjoyment responses to high-intensity interval training (HIIT) “excellent” and “much needed” but are also dismayed that they found other parts “flawed” and “inappropriate.” Respectfully, for the reasons we outline below, we cannot accept the final assertion that the arguments presented by Vollaard et al. “refute the intensity-related criticisms made by Ekkekakis et al. regarding the (in)appropriateness of the intensities used in HIIT protocols in various studies comparing the affective and enjoyment responses between HIIT and moderate or vigorous continuous exercise.”
Synopsis of the Point of Contention With Vollaard et al.
One of our concerns about the methodology of studies investigating affective and enjoyment responses to HIIT related to observations we have made that, in some studies, the levels of exercise intensity (typically, operationally defined through heart rate) reached by groups or experimental conditions described as “moderate-intensity continuous exercise” were as high as or even higher than the levels of exercise intensity reached by groups or conditions described as “high-intensity interval exercise.” In other words, the meaning of words was seemingly reversed, since something characterized as “moderate” was, in fact, as high as, or even higher, than something characterized as “high.” For example, we commented on a study (Kilpatrick et al., 2015) in which participants in sessions labeled as “HIIT” (or interval exercise of “heavy” or “severe” intensity) were transiently reaching heart rates as high as, or even lower than, the heart rates recorded consistently during extended sessions of continuous exercise. Then, not finding dramatically worse affective or enjoyment responses in the interval sessions compared with the continuous sessions, the authors attributed this finding to interval exercise having some yet-unidentified “special” properties: “there does appear to be something about interval exercise that protects against the predicted negative shift in affect that normally occurs during intense exercise” (p. 250). We suggested applying Occam’s razor (i.e., that the explanation was rather simple): The supposedly “intense” interval exercise was no more “intense” than the continuous exercise, and in addition, it was only performed intermittently (with breaks), while the continuous exercise was performed without breaks.
Vollaard et al. argue that using heart rate or oxygen uptake to quantify exercise intensity in the case of interval exercise is inappropriate. Instead, they assert that exercise intensity should be defined as a percentage of the peak workload achieved during a prior graded exercise test. For example, if continuous exercise is performed against a resistance of 40% or 50% of peak workload, it would be “moderate,” while, if interval exercise is performed against high resistance (e.g., corresponding to 90% or 100% of the highest workload achieved during a prior graded test), the intensity would be “high” (in the case of 90%) or “maximal” (in the case of 100%). This may sound reasonable and straightforward, but it is not. Let us explain.
In the case of continuous exercise, the workload may be only 40% or 50% of the peak value achieved during a prior graded exercise test but, depending on the level of cardiorespiratory fitness of the participant, it may exceed the lactate or ventilatory (gas-exchange) threshold and may therefore preclude the maintenance of physiological steady state. As a result, over an exercise session lasting 30, 40, or 50 min, indices of metabolic strain (e.g., heart rate, oxygen uptake, and blood lactate) and general physiological stress (e.g., catecholamines and cortisol) would continuously rise until people “max out” (i.e., approach 100% of their peak heart rate and/or oxygen uptake, and/or feel the need to terminate their volitional effort). According to Vollaard et al., in this scenario, “exercise intensity” would be “moderate” and should be considered as having remained constant during the session since the workload was approximately one-half of its maximal value and remained unchanged throughout the session.
In the case of interval exercise, the workload may be high (e.g., as much resistance on a cycle ergometer as the peak value reached during a prior graded exercise test), but if the duration of an interval is short (we cited examples of intervals as short as 4 s from the literature), then typical indices of metabolic strain would exhibit a relatively small response (e.g., within the range of heart rate or oxygen uptake typically considered indicative of “moderate” or “vigorous” intensity by the American College of Sports Medicine [ACSM]). According to Vollaard et al., in this scenario, “exercise intensity” would be maximal, since the workload corresponded to the peak value achieved during a prior graded exercise test.
For example, Vollaard et al. (2024) cited an example of a study in which participants were asked to go “all out” against heavy resistance on a cycle ergometer, but only for durations of 10, 15, or 20 s (Ruffino et al., 2017). Despite the heavy resistance, because of these very short durations, the participants only reached 86%, 87%, and 88% of their peak heart rate, respectively, during these intervals (i.e., values that fall within the “vigorous” range according to the classification of exercise intensities adopted by the ACSM). At the same time, ratings of perceived exertion remained in the 13–14 range on the 6–20 scale (i.e., “somewhat hard,” at the cusp between the “moderate” and “vigorous” ranges according to the ACSM). However, according to Vollaard et al. (2024), exercise intensity in that study was “supramaximal,” presumably because the workload on the cycle ergometer was greater than the workload that elicited the peak value of oxygen uptake.
A study coauthored by Dr. Jung and Dr. Little that was published in this journal offers a glimpse of the confusion that can result from defining the concept of “exercise intensity” in the manner advocated by Vollaard et al. The study (Martinez et al., 2015) compared one continuous-intensity condition, performed at 50% ± 4% of peak workload, and three interval conditions performed at 78% ± 2% of peak workload. While the workload of the three interval conditions was identical within participants, what differed was the duration of the intervals: (a) 30 s, (b) 60 s, and (c) 120 s. Because of these differences in interval duration, heart rate data indicated that the 30-s condition peaked at 149 bpm, the 60-s condition peaked at 168 bpm, and the 120-s condition peaked at 180 bpm. At the same time, the supposedly lower intensity continuous condition peaked at 167 bpm (i.e., nearly identical to the supposedly “higher intensity” 60-s interval condition and higher than the supposedly “higher intensity” 30-s interval condition).1 Following the logic of Vollaard et al., since all three interval conditions were performed at the same workload, their “exercise intensity” was identical—and higher than the “exercise intensity” of the continuous condition.
Contextualization of the Claims by Vollaard et al.
Vollaard et al. have spearheaded a movement within the exercise sciences that calls for the promotion of “diminutive” exercise stimuli as being sufficient to elicit significant gains in fitness and health variables. This movement has appeared in the literature under various names, including “reduced-exertion HIIT” and “low-volume HIIT.” Predictably, these claims have attracted considerable attention from exercise researchers, practitioners, journalists, and the general public because they seemingly upend long-established dogma in the exercise sciences, according to which the enhancement of fitness and health requires considerable investment of time and effort.
In the process of trying to discover the least amount of exercise that can be said to produce significant changes in fitness and health parameters, Vollaard et al. have made some of the most extraordinary claims that have appeared in the exercise science literature. For example, in an article titled “Towards the Minimal Amount of Exercise for Improving Metabolic Health,” Metcalfe et al. (2012) reported that maximal aerobic capacity can be increased by 14% (15% in men and 12% in women) after a total of only 9:30 min:s of training consisting of “all-out” cycling sprints, each lasting only 10–20 s. Remarkably, during these sprints, the average perceived exertion remained in the “moderate-intensity” range (13 ± 1 on the 6–20 scale). In another study, Songsorn et al. (2016) reported that even a training program totaling only 4 min of exercise (one 20-s sprint performed three times per week for 4 weeks) led to positive changes in maximal aerobic capacity in 11 of 15 participants (range 1%–21%), such that “the mean increase in VO2max in response to single-sprint training in a larger sample would reach significance” (p. 1516). In a subsequent meta-analysis, Vollaard et al. (2017) reported that doing less exercise per session (fewer sprints) does not diminish, and may even enhance, the gains in maximal oxygen uptake: “the improvement in VO2max with [sprint interval training (SIT)] is not attenuated with fewer sprint repetitions, and possibly even enhanced” (p. 1150). Moreover, the overall “dose” of training is allegedly irrelevant, since the effects of the total duration of the intervention, the number of sessions, the duration of each sprint, or the level of resistance were reportedly shown to have effects that are “unclear or trivial” (p. 1150).
Similarly, a recent review by Sabag et al. (2022) concluded that “low-volume” HIIT “can induce similar, and at times greater, improvements in cardiorespiratory fitness” compared with “high-volume” HIIT and moderate-intensity continuous training “despite requiring less time commitment and lower energy expenditure” (p. 1013, italics added). This is an astonishing claim because “low-volume” HIIT was said to differ from “high-volume” HIIT solely by entailing a lower total duration of high-intensity exercise (<15 min compared with ≥15 min). Otherwise, the two training modalities were said to share common features (e.g., intensity of 80%–100% of maximal heart rate or maximal oxygen uptake, same interval duration, and same work-to-rest ratio). In other words, the review concluded that, contrary to conventional wisdom in the exercise sciences, doing less exercise is “as effective as” or, remarkably, “more effective than” doing more exercise while holding other important aspects of the exercise “dose” constant.
The extraordinary claims by Vollaard et al. are not limited to the physiological advantages of “reduced-exertion HIIT” and “low-volume HIIT” but extend to the sphere of psychological responses, as well. In recent systematic reviews, Vollaard et al. have argued, for example, that SIT, which is a more strenuous form of HIIT, is “comparably” enjoyable and “similarly” pleasant compared with moderate-intensity exercise “despite its supramaximal intensity” (Hu et al., 2022, p. 1). The intensity of SIT is allegedly irrelevant, since whether sprints are performed at “all-out” or not “all-out” intensity has only “trivial” effects on how participants feel (Metcalfe et al., 2022, p. 9). Citing the previous meta-analysis by Hu et al. (2022); Vollaard et al. (2017) asserted that “given that physiological improvements elicited by SIT [are] not attenuated with shorter and fewer sprints,” the key to “more positive affective responses, thus potentially increasing future exercise adherence” (p. 11) is to do low-volume SIT “with shortened sprint duration and fewer sprint repetitions,” such as two 20-s sprints or ten 6-s sprints. Especially “decreasing the sprint duration in a [Sprint Interval Exercise] protocol may result in more positive affective responses” (p. 10).
Although HIIT/SIT, “reduced-exertion HIIT,” and “low-volume HIIT” have emerged as impressively popular trends in the exercise science literature, we have opted to remain skeptical. We have not yet seen methodologically robust evidence demonstrating that “diminutive” stimulations of the metabolic and cardiovascular systems, totaling only a few seconds per day, can result in meaningful improvements in exercise performance or maximal aerobic capacity. We are unconvinced by claims that doing less exercise is more effective than doing more (see Wen et al., 2019, for contrary evidence). Instead, we have been concerned about a host of methodological limitations that can readily provide alternative explanations for the extraordinary claims. We see extremely small samples (e.g., commonly in the range of five to 10 participants per group), absence of reproducible power calculations, frequent absence of control groups or randomized allocation to groups, complete lack of preregistration (i.e., no protection against selective outcome reporting), long lists of dependent variables unaccompanied by specific hypotheses, no distinction between primary and secondary/exploratory outcomes, absence of measures to address the inflation of the Type I error rate due to multiplicity, lack of blinding of the outcome assessors and statistical analysts, and rampant disregard for the distinction between superiority and equivalence/noninferiority hypotheses and associated statistical testing approaches (Mazzolari et al., 2022). For these reasons, until more robust methodologies prevail, we consider the extraordinary claims surrounding HIIT/SIT, “reduced-exertion” HIIT, and “low-volume HIIT” as primarily statistical and methodological phenomena rather than physiological phenomena.
We recently joined colleagues in sounding an alarm for the poor methodological and reporting standards in these literatures (Bonafiglia et al., 2022; Ekkekakis & Tiller, 2023; Ekkekakis, Swinton, & Tiller, 2023; Ekkekakis, Vallance et al., 2023; Hall et al., 2023). We urge the readers of JSEP to take these concerns into account when evaluating these lines of research and the accompanying claims. As one example, after critically appraising 27 studies investigating SIT, Bonafiglia et al. (2022) concluded that “all 27 studies included in our meta-analysis had a high risk of reporting bias” (p. 563). In particular, 26 of 27 studies examining the effects of SIT on maximal oxygen uptake used outcome assessors who were aware of group assignments. Because assessments of maximal oxygen uptake depend on how long participants can tolerate the aversive somatosensory stimulation associated with near-maximal exercise, the use of blinded outcome assessors is crucial. For example, unblinded outcome assessors, whose job security, academic promotion, or grant funding hinges on obtaining novel results may, deliberately or unwittingly, vary the frequency or volume of verbal encouragement in order to facilitate the desired outcome. Variations in verbal encouragement can comfortably account for the reported range of gains in maximal oxygen uptake from short-term interventions, namely 5%–15% (Midgley et al., 2018).
Similarly, regarding claims that low-volume SIT is just as “pleasant” or “enjoyable” as moderate-intensity continuous exercise, we have pointed out (Ekkekakis et al., 2023b) that, among other factors, these claims may be due to the timing of obtaining ratings of affect and enjoyment during exercise. It is probably not coincidental that studies investigating “reduced-exertion HIIT” and “low-volume HIIT” base their conclusions exclusively on ratings of affect and enjoyment obtained during the recovery periods that follow the sprint intervals. For example, ratings were obtained “immediately on completion of the sprints” (Songsorn et al., 2020, p. 720) or “immediately after” the sprints (Astorino et al., 2020, p. 2). It is well established that, especially among healthy participants, ratings of affect rebound toward positivity instantly and robustly upon the cessation of strenuous effort.
Why We Cannot Agree With Vollaard et al.
We cannot agree with this position for several reasons.Setting and reporting workloads relative to the maximum achieved during a prior incremental fitness test is sufficient for researchers, peer reviewers, editors, and critical readers, to understand the level of intensity, and to enable direct comparisons with the intensity applied in continuous exercise conditions.
- 1.It is important to keep in mind that our papers and the accompanying methodological checklist referred to studies investigating affective and enjoyment responses to HIIT (Ekkekakis et al., 2023a, 2023b). As we noted, the guiding theoretical framework for investigating affective and enjoyment responses to exercise, including HIIT and its variants, stems from “theorizing in the fields of affective psychology and neuroscience,” fields in which the “dimension of pleasure–displeasure is an integral component of consciousness that closely tracks changes in the homeostatic condition of the body” (Ekkekakis et al., 2023a, p. 77). According to a foundational text by Panksepp (1998), “sensations generate pleasure or displeasure in direct relation to their influence on the homeostatic equilibrium of the body” (p. 164, italics added). In other words, affective responses are theorized to have evolved for the purpose of relaying the severity of homeostatic perturbations to conscious awareness (Feldman et al., 2024; Strigo & Craig, 2016). Therefore, in the study of affective responses to exercise, the adjectives “moderate” and “high” intensity must refer to conditions that entail “moderate” and “high” perturbations in the major physiological systems of the body (Roloff et al., 2020).
- 2.In the common understanding of the fundamental training principle of overload, what is presumed to cause an adaptation is not the workload per se but rather stressing the relevant bodily systems beyond the level to which they are routinely pushed: “The overload principle refers to the fact that an organ system (e.g., cardiovascular) or tissue (e.g., skeletal muscle) must be exercised at a level beyond which it is accustomed to in order to achieve a training adaptation” (Powers & Howley, 2018; p. 295). The reason why “overload” is defined in this manner (i.e., by referencing the stress placed on the bodily systems rather than by referencing the workload) is because, regardless of the workload (e.g., the breaking force used on a cycle ergometer), it is assumed that no adaptation will occur unless the relevant systems of the body are stressed beyond the level to which they are accustomed. This can be illustrated by pushing the argument “ad absurdum” (i.e., to an absurd extent). Let us imagine that we set the braking force on the cycle ergometer to be equivalent to several times the peak workload, such that, despite the instruction to go “all out,” an individual would not be able to rotate the pedals more than once (i.e., similar to a one-repetition maximum) or not at all (i.e., a brief isometric contraction). Following the logic of Vollaard et al., exercise intensity in this scenario would be “supramaximal” (i.e., exceeding maximal workload severalfold). Such a stimulus (i.e., pushing without being able to rotate the pedals) would probably cause neuromuscular adaptations if done regularly. However, can we reasonably expect gains in maximal oxygen uptake if the relevant mechanisms (e.g., cardiac output, hemoglobin content, and oxygen utilization by the muscles) are not subjected to overload?
- 3.After being challenged to bring some degree of standardization to the definition of the concept of “high intensity” in the HIIT/SIT literature, leaders within this area of research, including Dr. Jonathan Little, recently presented what was intended as a “consensus” paper (Coates et al., 2023). The term “workload” was not used in this document even once. Instead, the experts wrote that “HIIT can be characterized as intermittent bouts performed above moderate intensity” (i.e., encompassing the range of “vigorous” intensity), as “demarcated by indicators related to perceived exertion, VO2, or heart rate as defined in authoritative public health and exercise prescription guidelines” (p. S87). In turn, SIT was defined as an “intense variant of HIIT and distinguished as repeated bouts performed with near-maximal to ‘all out’ effort that fall within the highest intensity classification included in some guidelines” (pp. S87–S88). Just as we had done months earlier when we criticized “arbitrarily selected percentages of maximal capacity” and advocated instead for “a system based on specific metabolic landmarks, such as the lactate or gas-exchange ventilatory threshold and the level of critical power” (Ekkekakis et al., 2023b, p. 94), the HIIT/SIT experts also noted that defining intensity in terms of percentages of maximal heart rate or maximal oxygen uptake “may not be optimal” and advocated instead for expressing exercise intensity “relative to ‘physiological’ thresholds such as critical power or speed” (p. 88). In other words, Dr. Little coauthored a consensus paper advocating for precisely the same perspective on the definition of “intensity” that we had expressed in our papers but subsequently coauthored a “letter to the editor” characterizing this same perspective as “flawed” (i.e., “the key section on operational definitions of ‘high’ and ‘moderate’ intensities’ in Part II of the review [Ekkekakis et al., 2023b] is flawed”) and “inappropriate” (i.e., “the concepts related to Item 6 from Ekkekakis et al. checklist are inappropriate”). We find the inconsistency between these positions confusing and not conducive to a productive scientific dialogue.
- 4.Unlike other systems to classify exercise intensity, including those that are grounded in physiology (e.g., Jamnick et al., 2020) and those based on conventions (e.g., ACSM), Vollaard et al. offered no system that would enable researchers or practitioners to decide how high a percentage of peak workload would have to be to merit the characterization “high” and what range of percentages of peak workload would merit the characterization “moderate.”
- 5.In support of their argument, Vollaard et al. cited a small study (N = 18; Bossi et al., 2023), affording very low accuracy in estimating the parameters of linear models, which compared different methods of setting the intensity of HIIT sessions, including 85% of the maximal work rate. Using exercise performance (i.e., time to exhaustion), physiological responses (e.g., lactate, cardiorespiratory responses, and muscle tissue oxygenation), and perceptual ratings (e.g., perceived exertion) during HIIT as criteria, the researchers concluded that all methods performed poorly in “normalizing” individual responses (i.e., reducing interindividual variability). Vollaard et al. interpreted this finding as demonstrating that using a percentage of peak workload “is not an inferior method for prescribing exercise intensity during HIIT.” Our interpretation is different. Notwithstanding the severe limitations of the study, the data demonstrated that setting the intensity of HIIT as a percentage of the maximal work rate resulted in widely disparate exercise performances, physiological responses, and perceptions of exertion. Our perspective aligns with expert reviews. Jamnick et al. (2020) concluded that “there is currently no evidence supporting the prescription of exercise intensity relative to [maximum work rate] or [maximum velocity] as a valid method for yielding a distinct and/or homogeneous homeostatic perturbation” (pp. 1737–1738). Iannetta et al. (2020) stated that “exercise intensity prescription using a [percentage of peak work rate]—even when associated to a ramp-incremental derived [percentage of maximum rate of oxygen uptake]—should be avoided” (p. 471).
- 6.Vollaard et al. wrote, “Ekkekakis et al. (2023b) claim that if measures of [heart rate] or [oxygen uptake] do not differ between HIIT and vigorous-intensity continuous exercise, then ‘HIIT would clearly offer no training advantage’ (p. 96).” However, we are unaware of literature suggesting that the adaptations associated with HIIT are mechanistically linked to an increase in [heart rate] or [oxygen uptake] during exercise. Conversely, there is strong evidence to support that adaptations to HIIT are related to the metabolic perturbations during the high-intensity bouts (MacInnis & Gibala, 2017).” It should be clear that saying that two modalities of exercise resulting in similar levels of heart rate or oxygen uptake should not be expected to yield different relevant training outcomes (e.g., maximal oxygen uptake or exercise performance) is not the same as saying that all training-induced adaptations “are mechanistically linked to an increase in [heart rate] or [oxygen uptake] during exercise.” It should also be clear that, when MacInnis and Gibala (2017) compared possible cellular adaptations with HIIT/SIT and moderate-intensity continuous exercise, such as mitochondrial function and content, they did not endorse the definition of “intensity” advocated by Vollaard et al. Instead, HIIT was defined as “‘near-maximal’ efforts generally performed at an intensity that elicits ≥80% (but often 85%–95%) of maximal heart rate” whereas moderate-intensity continuous training was defined as “exercise that is performed in a continuous manner and at lower intensities than HIIT” (pp. 2916–2918).
- 7.Vollaard et al. stated that “there is strong evidence to support that adaptations to HIIT are related to the metabolic perturbations during the high-intensity bouts.” This statement could have been the beginning of a convergence between our viewpoint (i.e., define “intensity” in reference to homeostatic perturbations taking place within the body) and theirs (i.e., define “intensity” in reference to workload). We both seem to agree that “perturbations” in relevant physiological systems are key to providing the “overload” that will yield training-induced adaptations. Sadly, this potential convergence did not materialize because Vollaard et al. could offer no examples of practical, measurable indicators of the “perturbations” they had in mind.
- 8.Vollaard et al. probably already agree that the concept of “exercise intensity” cannot be adequately defined or understood only through the prescribed workload, without taking the response of the major physiological systems of the body into account. We believe this is the case because they have alluded to this in other writings. Nalçakan et al. (2018) performed a 6-week training study, with three training sessions per week (i.e., 18 sessions in total), comparing sessions consisting of only two sprints that differed in duration between groups: one group (n = 17) increased their sprint duration up to 20 s (i.e., 10 s for Sessions 1–3, 15 s in Sessions 4–6, and 20 s in Sessions 7–18) while another group (n = 18) increased their sprint duration up to 10 s (i.e., 5 s in Sessions 1–3, 7.5 s in Sessions 4–6, and 10 s in Sessions 7–18). Both groups were asked to pedal “all out” against a resistance equal to 7.5% of each participant’s body mass. The limitations of the study notwithstanding, the researchers found a nearly threefold larger increase in maximal oxygen uptake in the group with the longer sprints compared to the group with the shorter sprints (i.e., 9.75% vs. 3.49%). Nalçakan et al. commented that although “it was suggested that generation of peak power is a key stimulus for improving VO2max,” their “data suggest that this is not the case” (p. 342). This, then, begs the question: Since the workload was the same, why would the longer duration of the sprints make a difference? Is it possible that, given the longer duration, the mechanisms underlying maximal oxygen uptake were exposed to a higher level of stress (i.e., overload; also see Astorino et al., 2023; Bogdanis et al., 2022)?
- 9.Vollaard et al. claimed that “the percentage of peak workload is straightforward to determine” and “an appropriate, practical, and accurate measure of exercise intensity during HIIT.” This view, however, is not widely held. “Peak workload,” which was left undefined by Vollaard et al., is not “straightforward to determine.” Experts warn that “there is no recommended protocol design for determining [the peak workload]” (Jamnick et al., 2020, p. 1737). Instead, there is ample evidence that the peak workload is protocol-specific and can be readily manipulated, for example, by using graded protocols that involve different slopes (Iannetta et al., 2020; Jamnick et al., 2020). Moreover, it is important to appreciate that “peak workload” should not be confused with the workload reached when individuals “max out” during a graded exercise test or with the workload reached when the criteria for maximal oxygen uptake are met. People can “max out” and maximal oxygen uptake can be achieved with a range of workloads that exceed the level of “critical power” (Keir et al., 2018). Therefore, contrary to the claims by Vollaard that the determination of “peak workload” is “straightforward,” both the definition of the concept of “peak workload” and the determination of this parameter are quite complex.
The hyperbolic claims in the literature investigating HIIT/SIT, “reduced-exertion HIIT,” and “low-volume HIIT” have fueled a polarized debate. In turn, this polarization has made scientific discourse difficult. As we did in our recent papers in JSEP (Ekkekakis et al., 2023a, 2023b), we maintain that, when investigating affective and enjoyment responses to exercise, it makes no sense to characterize an exercise condition that causes relatively minor homeostatic perturbations as being of “high intensity” and another exercise condition that causes a similar or higher degree of homeostatic perturbation as being of “moderate intensity.” For the reasons we outlined here, we remain unconvinced that defining “high” and “moderate” exercise intensity solely in terms of percentages of peak workload (i.e., without reference to homeostatic perturbations within the body) is a sensible option that can help minimize confusion in this important line of research.
Notes
Although the published article only contained heart rate data averaged over the entire duration of the exercise sessions (i.e., subsuming both interval and recovery periods for the three interval conditions), detailed heart rate data can be found in the master’s thesis by the lead author at https://digitalcommons.usf.edu/etd/4536
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