LAUSR

High-intensity interval exercise and high-intensity interval training (HIIT), an exercise approach alternating short bouts of vigorous exercise with less intense recovery or rest periods, has been rated as a leading fitness trend, ranked between #1 and #3 in the annual survey of “Top 20 Worldwide Fitness Trends” since 2014, with no sign of weakening “popularity” (Thompson, 2019). This increased popularity in HIIT programs has been mirrored by a subsequent uptick in related research. In such investigations, HIIT appears to deliver important physiological benefits (much like those observed by any regular exercise behavior; Kilpatrick et al., 2014; Jelleyman et al., 2015). However, little is known about why high-intensity interval programs have gained such popularity within the fitness industry (i.e., increasing number of high-intensity interval type franchises such as F45 R © Training, Orangetheory Fitness R , Crossfit R © Training, Bootcamps, and so on), let alone, and perhaps most importantly, whether such a regimen encourages prolonged exercise1 behavior (i.e., adherence). Based on previous work (e.g., Williams et al., 2008) with continuous exercise, the affective experience of such HIIT-type programs may be a particularly important reason why it is popular. Thus, we will address some methodological concerns pertaining to HIIT research, specifically related to the study of affective states. We will also propose potential solutions for investigating such psychological phenomena associated with this popular exercise regimen.