Effect of a muscle pause phase on repetition performance and muscle activity dynamics during slow squat exercise using body weight

The slow squat exercise using body weight (SQ) has training benefits in healthy individuals and may be applicable in rehabilitation settings. Including or excluding a pause phase during muscle exertion may provide greater flexibility; however, no studies have examined its effects on exercise performance or muscle activity. This study clarified the impact of a pause phase during SQ on the number of repetitions and the dynamics of muscle activity. A crossover trial included seven young adult male individuals performing SQs without a pause phase (CON; transition to the next repetition with slight knee flexion), and with a pause (FEA; with the knee fully extended). Concentric-eccentric movements lasted 3 s, with a 1-s pause, and continued until volitional exhaustion. The number of repetitions (NR) until exhaustion and integrated electromyography (EMG) of the rectus femoris and vastus lateralis during exercise were normalized to the %EMG obtained during the isometric maximal voluntary contraction of knee extension. The NR until exhaustion was approximately two-fold higher in the FEA group than in the CON group (p < 0.001). The %EMG of the rectus femoris for repetitions 1–40 was significantly lower in the FEA group than that in the CON group (p < 0.01). A strong positive correlation was observed between the rate of change in the NR until exhaustion and the rate of change in rectus femoris activity (r = 0.82, p < 0.05), suggesting that incorporating a pause phase during SQ alters rectus femoris activity during movement and may enhance exercise endurance.