DYNAMIC VARIABLES AND INJURIES IN RUNNING

PROCEDURES Baseline biomechanical data were collected on 143 runners prior to the beginning of the summer running season. All subjects wore their own footwear, which they used during the running season. Kinematic data were collected using a 4-camera high-speed (240 Hz) 3dimensional motion analysis system. Reflective markers (3 per segment) were placed on the rearfoot, lower leg and upper leg. Kinetic data were collected (1000 Hz) using a force platform. Three trials were collected per subject. The running speed (4.0 +/- 0.2 m/s) was monitored using two photo-cells at shoulder height. During a 6 month running period, subjects documented any injuries that developed. An injury was defined as any stoppage or decrease in running mileage. The influence of impact forces and impact loading rates, shoe eversion, shoe eversion velocity and resultant knee joint moments (abduction and external rotation) on injury were analyzed. For each variable, subjects were divided into three groups: the bottom 25%, the middle 50% and the top 25%. Injury rates for the different groups were compared using a Chi-square test (α=0.05). RESULTS Of the original 143 runners who started the study 83 completed the study. 66 of the 83 runners (80%) sustained an injury during the six month training period. There were no significant differences between injury rates for the low, mid and high groups for any of the variables analyzed. This was true despite differences in group injury rates of up to 30% in some instances (Table 1). Thus, it is possible that a larger number of subjects may have resulted in significant differences. The resultant knee joint moments showed the largest differences in injury rates where subjects with high knee joint moments had 20-30% more injuries than subjects with lower knee joint moments. The impact forces and loading rates showed the smallest differences in injury rates where differences between the different groups ranged from 3-5%.