Intra-set rest preserves barbell velocity during a free-weight back squat exercise by shifting energy system contribution.

In this study, we compared acute metabolic responses and barbell velocity loss (VL) during cluster set (CS) versus traditional set (TS) resistance exercise. Six strength-trained individuals completed two randomized crossover sessions of back squats. The CS protocol included 30 s intra-set rest intervals after the second and fourth repetitions, whereas the TS protocol used continuous repetitions. Barbell velocity, oxygen uptake and blood lactate concentrations were measured to derive model-based indices of energy system engagement. CS were associated with better preservation of barbell velocity and lower blood lactate concentrations compared with TS. Model-based indices suggested distinct metabolic patterns between set structures, with CS being associated with a higher alactic and lower lactic component than TS. Inter-individual responses were consistent across most participants. These findings indicate that acute metabolic and mechanical responses differ between CS and TS configurations. CS were associated with reduced indices of metabolic stress alongside improved velocity preservation, highlighting that set structure can influence the acute physiological-performance profile of resistance exercise.