COMPARISON OF RIGHT VS. LEFT LEG GRF LANDING SYMMETRY FOR HEALTHY AND OVERUSE INJURY-PRONE RECREATIONAL ATHLETES
AbstractPURPOSE AND METHODS The purpose of the study was to compare right versus left leg symmetry during landing for healthy (n = 10) and overuse injury-prone (n = 10) recreational athletes. Landing symmetry was evaluated by examining vertical ground reaction force (GRF; 1000 Hz) magnitude and temporal variables for each leg and subject group while landing from three different heights (50, 100, and 200% of maximum vertical jump, MVJ). Magnitudes of the first (Fl) and second (F2) maximum force values were identified along with the temporal occurrences of these events (T1 and T2, respectively). Vertical GRF pattern consistency varied among subjects and across heights, therefore, when Fl and F2 could not be individually identified the maximum force magnitude and temporal values for the landing phase were assigned to the F2 and T2 variables, respectively. The F2 and T2 values were utilized to evaluate differences between legs (one-way Analysis of Variance, ANOVA; = 0.05) for each group and landing height. Additionally, GRF pattern consistency between right and left legs (for both subject groups) was monitored by a tally which tracked the number of unimodal (single peak) curves for each landing height. RESULTS Results of the ANOVA procedures indicated no significant differences (p > 0.05) between the right and left side GRF magnitude or temporal variables for the healthy subject group. The injury prone group exhibited significant right-left side differences for the 50% MVJ height (p < 0.01; right greater than left) and for the 100% MVJ height condition (p < 0.05; right greater than left). No right-left temporal differences were observed for the injury prone group. Results of the descriptive GRF tally for the occurrence of unimodal landing curve patterns suggest that the injury prone group might have been more consistent between legs in producing traditional bimodal GRF-time histories. A unimodal curve was defined as a GRF-time history that did not follow the typical bimodal (Fl-toe, F2-heel) landing pattern. The 50% MVJ height elicited a right-left unimodal curve count of 21 and 30, respectively, for the healthy group and 19 and 19, respectively, for the injury prone subjects. For the 100% MVJ height condition the healthy group exhibited a total (sum of all subjects) of two right side and three left side unimodal curves, while the injury prone group exhibited no unimodal curves from either leg. No unimodal curves were detected for either subject group while landing from the 200% MVJ height. CONCLUSIONS The functional significance of these results is not clear. However, one might speculate that the asymmetrical GRF magnitude values observed for the injury prone group are related to their injury history, although the causeeffect relationship cannot be determined from these data. The number of differences between right and left leg unimodal curves might be related to the amount of movement variability exhibited by each subject group. The fewer total number of unimodal curves and the fewer number of right-left differences suggest less performance variability for theinjury prone group.