Purpose: To investigate the effect of rest duration on self-selected intensity, physiological responses, and RPE during a standardized, high-intensity interval training prescription.
Subjects: Nine well-trained male runners (V̇O2max 71 ± 4 mL·kg-1·min-1) performed three treadmill interval training sessions running at constant 5% incline. Six 4-min work bouts with either 1-, 2-, or 4-min recovery periods were performed in each session. Sessions were prescribed as high-intensity workouts with the goal being to achieve the highest possible average running speed for the work intervals. Subjects regulated their work and rest intensity based on these instructions. In a fourth interval session, subjects self-selected recovery time in response to a fixed intensity.
Results: Running velocity increased slightly (14.7 ± 0.7 vs 14.4 ± 0.8 km·h-1, P = 0.02) when rest increased from 1 to 2 min, but showed no further increase with a 4-min rest (14.7 ± 0.6 km·h-1). Work V̇O2 was slightly higher with a 2-min rest duration compared with 1 and 4 min (66.2 ± 4.2 vs 65.1 ± 4.2 and 64.9 ± 4.7 mL·kg-1·min-1, P < 0.05). Peak blood lactate was similar (6.2 ± 2.6, 6.8 ± 2.9, 6.2 ± 2.6 mmol·L-1) across conditions, whereas peak RPE was slightly lower during the 4-min rest condition (17.1 ± 1.3, 17.7 ± 1.5, 16.8 ± 1.5, P < 0.05). With self-selected recovery time and no knowledge of elapsed time, the average rest duration was 118 ± 23 s.
Conclusions: Under self-paced conditions, varying rest duration in a range of 1 to 4 min had limited impact on performance during repeated 4-min high-intensity exercise bouts. Approximately 120 s of active recovery may provide an appropriate balance between intracellular restitution and maintenance of high V̇O2 on-kinetics.