Position-specific sagittal-plane right knee kinematics during spike take-off in male volleyball players

This study compared sagittal-plane right knee kinematics during position-specific spike take-off tasks among male volleyball outside hitters (OH), middle blockers (MB), and opposite hitters (OP). Twenty-seven male volleyball players classified as national first-level athletes were recruited and divided into three groups according to playing position, with nine athletes in each group. A three-dimensional motion capture system was used to collect right knee kinematic data. The instant of right-foot contact during the final approach step, the instant of minimum right knee angle, and the instant of bilateral take-off were defined as T1, T2, and T3, respectively. Right knee angle at key events, as well as the duration, range of motion, and phase-average angular velocity during the braking, propulsive, and total take-off phases, were analyzed. All three groups showed a similar kinematic pattern, with the right knee angle decreasing from T1 to T2 and increasing from T2 to T3. MB players showed significantly larger right knee angles at T1 and T2 than OH and OP players (162.04 ± 3.33° and 106.69 ± 8.02°, respectively; p < 0.001). OP players had the longest propulsive and total take-off durations, whereas MB players had the shortest durations (p < 0.001). Propulsive range of motion differed significantly among groups (Holm-adjusted p = 0.004), with OP players showing the greatest value (72.80 ± 9.30°) and larger values than OH and MB players. Total range of motion remained significant in the primary analysis (Holm-adjusted p = 0.030), with OP players showing larger values than MB players; however, this finding was not confirmed by the Holm-adjusted supplementary Kruskal-Wallis analysis and should therefore be interpreted cautiously. These findings characterize between-group differences in sagittal-plane right-knee kinematics under position-specific spike take-off task conditions. MB players showed larger right-knee angles and shorter take-off durations, OP players showed greater propulsive right-knee range of motion, and OH players showed intermediate values for several variables. These findings may help coaches identify right-knee kinematic variables to monitor within position-specific spike take-off training tasks.