Load-specific post-activation performance enhancement from back squats in male collegiate basketball players: moderate loads preferentially enhance jump performance and lower-limb EMG activation.

Purpose: To compare the acute effects of pre-activation with different loads of back squat on multiple jumping performances and lower limb electromyographic (EMG) activity in male collegiate basketball players, and to provide evidence for load selection and timing of pre-game warm-up activation. Methods: In a randomized, parallel-group controlled design, 40 male collegiate basketball players meeting inclusion criteria were assigned to 70%, 80%, 90% 1RM squat groups and a control group. Each experimental group performed 3 sets × 4 repetitions of parallel back squat as a conditioning activity (CA), while the control group rested quietly. Countermovement jump (CMJ), squat jump (SJ), approach vertical jump (AVJ), and standing long jump (SLJ) were assessed before intervention and at 4, 8, and 12 min post-intervention. Ground reaction force and surface EMG of 8 muscles on the dominant lower limb were recorded simultaneously during CMJ and SJ. Jump height/distance, reactive strength index (RSI), elastic utilization ratio (EUR), and EMG root mean square (RMS) were calculated. A 4 (group) × 4 (time point) repeated-measures ANOVA was applied. Results: Jumping performance showed significant main effects of time under different squat loads, with peak post-activation performance enhancement (PAPE) mainly occurring at 8-12 min post-CA. Compared with 90% 1RM, the 70%-80% 1RM groups exhibited more stable improvements in CMJ, SJ, AVJ, and RSI, along with more consistent within-muscle increases in normalized RMS for rectus femoris (RF), biceps femoris (BF), and lateral gastrocnemius (LG), with minor changes in EUR. Conclusion: Moderate-load back squat CA induces marked PAPE in male collegiate basketball players within a short time window, with 8-12 min being the optimal period for performance enhancement. Within the load range of this study, moderate-to-high intensity squat appears more effective than high-intensity conditions in acutely improving jumping performance and enhancing within-muscle normalized EMG responses in selected lower-limb muscles. Descriptively, considering static and reactive jump indices and EMG outcomes together, 80% 1RM showed a favorable overall response pattern in this sample, without implying direct statistical superiority over 70% 1RM These findings provide a reference for optimizing basketball-specific warm-up activation programs.