Decreasing sprint duration from 20 to 10 s during reduced-exertion high-intensity interval training (REHIT) attenuates the increase in maximal aerobic capacity but has no effect on affective and perceptual responses

Purpose: Recent studies have demonstrated that modifying the ‘classic’ 6x30-s ‘all-out’ sprint interval training (SIT) protocol by incorporating either shorter sprints (6x10-s or 15-s sprints) or fewer sprints (e.g. 2x20-s sprints; reduced-exertion high-intensity interval training (REHIT)) does not attenuate the training-induced improvements in maximal aerobic capacity (VO2max). The aim of the present study was to determine whether reducing the sprint duration in the REHIT protocol from 20 s to 10 s per sprint influences acute affective responses and the change in VO2max following training.  Methods: Thirty-six sedentary or recreationally active participants (17 women; mean±SD age: 22±3 y, BMI: 24.5±4.6 kg·m-2, VO2max: 37±8 mL·kg-1·min-1) were randomised to a group performing a ‘standard’ REHIT protocol involving 2x20-s sprints or a group who performed 2x10-s sprints. VO2max was determined before and after 6 weeks of 3 weekly training sessions. Acute affective responses and perceived exertion were assessed during training.  Results: Greater increases in VIO2max were observed for the group performing 20-s sprints (2.77±0.75 to 3.04±0.75 L·min-1; +10%) compared to the group performing 10-s sprints (2.58±0.57 vs. 2.67±3.04 L·min-1; +4%; group×time interaction effect: p<0.05; d=1.06). Positive affect and the mood state vigour increased post-exercise, while tension, depression and total mood disturbance decreased, and negative affect remained unchanged. Affective responses and perceived exertion were not altered by training and were not different between groups.  Conclusion: Reducing sprint duration in the REHIT protocol from 20 s to 10 s attenuates improvements in VO2max, and does not result in more positive affective responses or lower perceived exertion