The impact of rest duration on work intensity and RPE during interval training.

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 (VO(2max) 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 VO(2) 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 VO(2) on-kinetics.