Exploring Acute Physiological Adaptations to Circuit Strength Training: The Role of Work-to-Rest Interval Variations.

This research examined the acute physiological responses to circuit strength training performed with different work-to-rest interval durations (10:10, 20:20, and 30:30 seconds) under a constant 1:1 ratio. Thirty-four trained adults (15 males and 19 females) completed 14-minute circuit protocol with two blocks of 6-minute separated by a 2-minute rest period. Each session comprised six alternating upper- and lower-body exercises performed at maximal intended velocity. Heart rate was continuously recorded during the protocol, while blood lactate concentration, countermovement jump height, and 10-metre sprint performance were assessed pre-, mid-, and post-circuit session. Repeated-measures ANOVA was used for countermovement jump height, blood lactate concentration and 10-metre sprint performance, and one-way ANOVA for heart rate data. The 30:30 protocol elicited the highest post-exercise lactate concentrations (p < 0.05) and the largest decrements in CMJ height. Conversely, heart rate was consistently higher in the 10:10 protocol across several time points (p < 0.01), suggesting increased cardiovascular demand under shorter rest durations. Sprint performance showed a moderate decline across all protocols, with the greatest deterioration observed following the 10:10 condition. These results demonstrate that the manipulation of absolute work-to-rest durations, even under a fixed 1:1 ratio, produces distinct physiological and performance responses. Longer intervals (30:30) maximize metabolic stress and neuromuscular fatigue, whereas shorter intervals (10:10) enhance cardiovascular load. The 20:20 protocol represents a balanced alternative between both stimuli.