Intra-Set Velocity Decline and Set-to-Set Changes During a Standardized Moderate-Load Back Squat Protocol in Trained Track and Field Athletes

Velocity-based training (VBT) is widely used to monitor resistance training intensity and fatigue through movement velocity. However, repetition-by-repetition velocity behavior and set-to-set fatigue responses under standardized moderate-load conditions remain insufficiently characterized in trained athletes when the primary goal is monitoring. This study examined intra-set velocity decline and set-to-set changes during a standardized back squat protocol at 60% one-repetition maximum (1RM) in trained track and field athletes. Twelve athletes performed two sets of five repetitions while barbell velocity was recorded using a linear velocity monitoring device. Mean concentric velocity (MCV) was analyzed repetition-by-repetition, and key velocity-derived metrics (V1, Vmean, V5, velocity loss, and intra-set velocity slope) were calculated. MCV decreased progressively across repetitions within both sets (p < 0.001). Velocity declined from 0.787 ± 0.096 to 0.664 ± 0.087 m·s−1 in set 1 and from 0.760 ± 0.088 to 0.622 ± 0.084 m·s−1 in set 2. Significant set-to-set reductions were observed for V1, Vmean, and V5 (all p < 0.001), accompanied by greater velocity loss and a steeper intra-set decline. These findings provide context-specific reference points to assist in interpreting velocity responses for monitoring neuromuscular fatigue during moderate-load resistance training.