Acute neuromuscular fatigue in circuit strength training: effects of varying work-to-rest durations

Circuit training (CT) is a time-efficient resistance training method widely used to elicit neuromuscular and metabolic adaptations. However, the influence of different work-to-rest interval durations within a fixed 1:1 ratio on acute neuromuscular fatigue remains unclear. The present study aims to examine the acute effects of different 1:1 CT work-to-rest interval durations (10s, 20s, and 30s) on neuromuscular fatigue.

Thirty-four physically active participants (15 males and 19 females) completed 14-min CT protocols, each consisting of two 6-min blocks separated by a 2-min rest period and involving six alternating upper- and lower-body exercises (leg press, bench press, unilateral right knee extension, bilateral row, unilateral left knee extension, and seated overhead press). CT includes six exercises alternating lower- and upper-body movements. Mean propulsive velocity (MPV) was measured for squat (SQ) and bench press (BP) exercises before and after each session, and the total number of repetitions performed per exercise and set was recorded.

A significant main effect of time (pre- vs. postdata) was observed for MPV in both the SQ (p < 0.001) and the BP (p < 0.001) exercises. Velocity loss revealed significant differences between the SQ and the BP exercises (p < 0.001). The 30:30 protocol consistently performed a higher repetition rate (0,612-0,806 rep/s) compared with both 10:10 (0,488-0,768 rep/s) and 20:20 (0,488-0,754 rep/s) protocols.

A significant reduction in MPV was observed following all protocols, indicating the presence of acute neuromuscular fatigue regardless of interval duration. Although no statistically significant differences in fatigue magnitude were detected between protocols, work-to-rest interval duration influenced repetition output and execution characteristics, with the 30:30 protocol allowing greater repetition volume compared with the 10:10 and 20:20 protocols.