Inter-Repetition Rest Interval Affects Peak Power Independent Of Its Rate Of Development

Abstract

Numerous variables influence performance in resistance training. The duration between sets has been explored both for its acute effect on the subsequent set as well as its effect on the physiological responses to exercise. However, the duration of rest between repetitions is relatively unexplored. PURPOSE: To evaluate the effect of inter-repetition rest interval (IRRI) duration on power parameters within a single set. METHODS: We tested 206 healthy men and women between the ages of 15 and 70 using Proteus technology (Proteus Motion, USA). Subjects performed 36,728 repetitions across 4,566 sets of 25 exercises at various loads (1lb to 25lb) of three-dimensional isotonic resistance. Proteus software calculated the IRRI duration (milliseconds) and each repetition's peak power (watts) and peak force development rate (watts/sec). Linear regression models tested the effect of IRRI duration on the peak power and peak force development rate of the subsequent repetition while controlling for other significant predictors. RESULTS: In upper body motions, holding constant exercise performed (p<0.001), resistance applied (p<0.001), and repetition number (p=0.045), each additional second of IRRI predicted a 2.23-watt increase of peak power in the next repetition (p<0.001; 95% CI: 1.81-2.65). The overall model was significant (R2=0.613; p<0.001). Lower limb motions displayed a similar pattern (R2=0.620; p<0.001) but the magnitude of effect by IRRI duration was smaller (p=0.001; β=1.13; 95% CI:0.67-1.59). Lower limb peak force development rate was unaffected by IRRI (p=0.714); in upper body motions, there was a weak negative trend (β=-2.08; p=0.090). At loads under 20lb, IRRI was less influential to performance; for loads of 20-25lb, the optimal IRRI duration was 2.50-3.00 seconds. Holding confounders constant, repetitions that followed this duration of IRRI experienced a 40.99-watt increase in power (p<0.001; 95% CI: 17.76-64.22). That duration had no effect on peak force development rate (p=0.443). CONCLUSIONS: Performance in resistance training is affected by innumerable factors. Our findings add one more for consideration: the duration of rest between repetitions within a single set. To achieve maximum power in the subsequent repetition, a rest interval of 2.50 to 3.00 seconds appears ideal.