LAUSR

In their comment on our meta-analysis [1], Conceição et al. [2] suggest that a potential difference in caloric expenditure, as opposed to the difference in physiological responses, contributes to the variations in outcomes between interval training groups. We disagree with this claim for a number of reasons. Our meta-analysis examined the effects of highintensity interval training (HIIT) versus sprint interval training (SIT) on time-trial performance in participants who were recreationally active up to and including those who were competitive endurance athletes [1]. The literature cited in the comment by Conceição et al. [2] compares the effects of interval training with moderate intensity continuous training (MICT) in participants with cardiovascular pathology such as heart failure and coronary artery disease [3, 4]. On its face, this appears to be a comparison of apples to oranges. We are uncertain if the results from our review can be generalized to individuals with existing pathology for a number of reasons. First, patients with cardiovascular pathology respond differently to exercise, including slowed oxygen uptake kinetics, which may be critical to interval training responses [5, 6]. In addition, patients with heart failure are typically on medications such as beta-blockers which may further influence acute cardiovascular responses to exercise [7, 8]. Furthermore, there are also differences in the exercise interventions discussed in our review and those presented in the literature referenced in the Conceição et al. [2] comment as we did not compare interval training with MICT. Our review compared HIIT with SIT; once again, apples to oranges. In their discussion, Conceição et al. [2] suggest that there is no difference in outcomes when interval training and MICT are matched for caloric expenditure in individuals with cardiovascular pathology. The problem with this claim is that the various methods used to program interval and MICT exercise make it difficult to accurately determine the intensity or differentiate between the two modes of exercise. A number of studies in the cited reviews programmed the interval and MICT groups using similar intensities [9], used different methods to program intensities for the interval and MICT groups [10–12], or did not provide a specific exercise intensity for the interval group [13]. Many of the exercise programs cited used heart rate to program intensity [3, 4]. Previous literature in patients with heart failure using heart rate to set exercise intensity found that heart rate inaccurately represented the true training intensity. For example, the results of a large study (n = 261) by Ellingsen et al. [12] (also cited in the review [1]) found that approximately 50% of individuals performing interval training exercised below the prescribed intensity. Also, this study showed that 80% of individuals performing MICT exercised above their target values [12]. Overall, the lack of consistency in intensity programming makes it difficult to claim that caloric expenditure is the primary factor influencing changes in maximal oxygen consumption (VO2max) when exercise intensity is not precisely controlled. Previous work from Martin Gibala’s laboratory conducted in healthy individuals that compared interval This comment, reply and theparent article refers to the article available at Doi: https ://doi.org/10.1007/s4027 9-020-01264 -1.