Kinetic Analysis of Drop Landing: Comparison of Volleyball Players and Novice Subjects

This study investigates landing kinetics and postural stability of skilled volleyball players (n=6) and novice subjects (n=6). 12 healthy young females voluntarily participated in the study. The amplitude and temporal profile of the ground reaction forces (GRFs) which correspond to double-leg landing from a drop and subsequent 20-s quiet stance were analyzed. Dynamic and static postural stability performances were determined. Contact time (t0), maximal vertical GRF (VGRFmax), time to VGRFmax (tmax) and Loading Rate (LR) were calculated. The time that elapsed from t0 until the VGRF reaches to one body weight was determined (tDS:dynamic postural stability duration). Center of Pressure (COP) Velocity (COPV), Ellipse Area (EA), and Range were calculated from the COP trajectory during the quiet stance phase (tSS:static postural stability period). Mann Whitney U test was used to compare VGRFmax, dynamic and static postural stability between groups. Whereas, VGRFmax (p=0.015) and LR (p=0.004) were found to be lower, tDS (p=0.001) took longer in volleyball players. The differences between groups were statistically significant. There was a tendency to increase in tDS with the increase in VGRFmax and LR. Spearman rank correlation analysis revealed a moderate and a weak negative correlation between tDS with both VGRFmax (rs=-0.461, p<0.001) and LR (rs=-0.276, p<0.001) respectively. COP parameters for quiet stance were not significantly different between groups. Contrary to COPV, COP EA and Range were slightly higher in the novice group. The results of this study provide further insight into postural control strategies in skilled and novice subjects which might be related with vulnerability to potential musculoskeletal injuries and differences in postural stability performances