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 ([latin capital V with dot above]O2max 71 +/- 4 mL[middle dot]kg-1[middle dot]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[middle dot]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[middle dot]h-1). Work [latin capital V with dot above]O2 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[middle dot]kg-1[middle dot]min-1, P < 0.05). Peak blood lactate was similar (6.2 +/- 2.6, 6.8 +/- 2.9, 6.2 +/- 2.6 mmol[middle dot]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 [latin capital V with dot above]O2 on-kinetics.
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