Lower-limb kinematics and relative EMG amplitude distributions during role–task-specific volleyball spike-jump take-off in middle blockers and opposite hitters

Background Volleyball spike-jump take-off requires coordinated lower-limb movement, yet take-off organization during customary attack tasks of middle blockers (MBs) and opposite hitters (OPPs) remains unclear. This study compared lower-limb kinematics and relative EMG amplitude distributions during near-net quick attacks by MBs and back-row diagonal attacks by OPPs. Methods Eighteen male Chinese National Level I volleyball athletes (9 MBs and 9 OPPs) performed their corresponding customary attack tasks. Synchronized three-dimensional motion capture and bilateral lower-limb surface electromyography were recorded. Each athlete completed six formal trials, and three nationally qualified volleyball referees selected the trial that best met predefined task criteria by consensus. Because player position and attack task were coupled, comparisons represented role–task contexts rather than independent effects of either player role or attack task. T1–T3 and T3–T4 were defined as operational kinematic intervals separated by the instant of maximum right-knee flexion. Results The OPP task showed a longer T3–T4 interval (0.17 ± 0.01 vs. 0.12 ± 0.01 s; adjusted p = 4.98 × 10 -9 ) and total take-off time (0.43 ± 0.02 vs. 0.35 ± 0.03 s; adjusted p = 2.64 × 10 -5 ; Hedges’ g = 2.94) than the MB task. Most statistically significant ankle- and knee-angle differences occurred at T1, T2, and T3; at T4, significant differences were detected for both ankle angles but not for either knee angle. Relative RMS amplitude shares also differed between the role–task contexts, but these findings remain exploratory. Conclusion The two role–task contexts demonstrated distinct temporal and bilateral joint-motion profiles, together with exploratory differences in relative EMG signal distributions during take-off. Take-off duration and bilateral joint-angle change measures warrant further evaluation as candidate measures for task-specific assessment.