Impact of circuit training structures on the acute response in physiological and mechanical performance: a cross-sectional study.

This study analyzed physiological and mechanical responses to different circuit resistance training structures in young adults. A descriptive cross-sectional study was conducted to evaluate the acute effects of four distinct circuit resistance training protocols on blood lactate, heart rate, and countermovement jump (CMJ) mechanical variables in 30 experienced young adults. The training sessions differed in both exercise order (alternated vs. grouped) and training volume (maximal vs. submaximal repetitions): A1 (alternated, maximal), G1 (grouped, maximal), A2 (alternated, submaximal), and G2 (grouped, submaximal). Each protocol included upper and lower limb exercises performed on guided machines with standardized rest intervals. Mechanical properties of the CMJ were assessed before and after each session, lactate concentrations were measured pre-, mid-, and post-exercise, and heart rate was continuously monitored throughout all sessions. Results showed no significant differences in CMJ height between groups; however, power-related variables experienced greater declines in the high-volume protocols (A1 and G1). The rate of force development was also more negatively affected in these higher-volume conditions. Mid-session blood lactate levels differed significantly across groups, particularly between high- and low-volume protocols, although no differences were observed at the end of the sessions. Heart rate varied significantly between the 4th and 12th minute of exercise, reflecting the influence of volume rather than exercise order. In conclusion, training volume appears to be the primary factor influencing both physiological and mechanical responses during circuit resistance training, rather than the specific configuration of the exercises.