Effects of injury proneness and task difficulty on joint kinetic variability

Purpose: The purpose was to investigate the effects of lower extremity over use injury proneness and landing height on the variability of selected join t moment characteristics. Methods: Ten subjects from each of two groups (he althy and injury prone) performed 10 landings from a platform (heights: 50, 100, and 200% of maximum vertical jump). Force platform (1000 Hz) and vide o (200 Hz) information were collected and used to compute ankle, knee, and hip joint moment values during impact (0-100 ms post contact). Moment peak, time to peak, and impulse values were used to determine variability across 10 trials for each subject and height. MANOVAs and univariate follow-up te sts were used to assess variability differences between groups and among he ights. Results: Results revealed ankle moment variability differences (P le ss than or equal to 0.05; Tukey) between groups fur peak and time to peak v ariables at the 100% and 50% heights, respectively. The injury-prone group exhibited greater variability fur the peak variable, whereas the healthy gr oup showed greater variability fur the temporal variable. Groups also diffe red on the impulse variables (P less than or equal to 0.02; MANOVA), but fo llow-up tests failed to determine specific joints or directions of differen ces. Both groups exhibited tendencies fur St eater variability (P less than or equal to 0.05; Tukey) with increases in height up to 100% MVJ and decre ases in variability with further height increases. Conclusions: Results sug gest that groups differed in joint moment variability, possibly indicating a relationship between variability and overuse injuries, although the varia bles and directions of differences were inconsistent. For some variables, v ariability increased and then decreased with height increases for both grou ps, suggesting a range of heights within which the neuromuscular system ada pted.