We assessed the short-term effects of varying the volume of high-intensity interval training (HIIT) on psychological and physiological responses of 23 healthy adult males ( M = 21 years; M peak oxygen uptake [VO2peak] = 47.2 ml·kg-1·min-1). Participants were randomly assigned to low- and very-low-volume HIIT groups and engaged in nine supervised exercise sessions over three weeks. The low-volume HIIT group performed 8-12 60-second work bouts on a cycle ergometer at the peak power output achieved during the incremental test, interspersed by 75 seconds of low-intensity active recovery. The very-low-volume HIIT performed 4-6 work bouts with the same intensity, duration, and rest intervals. During training, participants' ratings of perceived exertion (Borg Category Ratio-10 scale) and their affective responses (Feeling Scale -5/+5) during the last 15 seconds of each work bout were recorded. Physiological data were VO2peak, endurance, and anaerobic performance before and after the intervention. Throughout training, participants in the very-low-volume group (relative to the low-volume group) reported lower ratings of perceived exertion in Week 1 ( M = 4.1 vs. M = 6.3; p < .01) and Week 3 ( M = 4.0 vs. M = 6.2; p < .01), and higher affective response in these same two weeks (Week 1: M = 1.9 vs. M = 0.3; p = .04; Week 3: M = 2.1 vs. M = 0.9; p = .06). Regarding physical fitness, Wingate peak power increased significantly after training in the very-low-volume HIIT group ( M = 1,049 W vs. M = 1,222 W; p < .05), but not in the low-volume HIIT group ( M = 1,050 W vs. M = 1,076 W). No significant change was found after training in physiological variables of peak power output, VO2peak, and endurance performance. In summary, in this short-term training period, the very-low-volume HIIT enhanced anaerobic capacity and was perceived as less strenuous and more pleasurable than low-volume HIIT.
Keywords: aerobic fitness; affective responses; feeling states; interval training; perceived exertion; physiological responses.