Differences in Lower Extremity Kinematic Variability between Healthy Runners Classified as Low or High Mileage

Abstract

Evidence suggests that running mechanics may differ between runners based on their weekly mileage; greater weekly mileage (WM) may act as a protective mechanism against injury. While the interaction between coordination patterns and WM has been investigated, interaction between lower extremity (LE) kinematic variability and WM has not. PURPOSE: To compare changes in LE kinematic variability between low (LM) and high mileage (HM) healthy runners after a prolonged run. METHODS: 23 healthy participants (27.4±7.7 yrs., 1.70±0.11 m, 67.9±15.4 kg, 16.3±5.6 km/week) were included in the LM group, while 12 participants (25.1±6.3 years, 1.71±0.1 m, 65.8±9.4 kg, 46.9±14.5 km/week) were included in the HM group. Participants ran on a treadmill for 30 minutes at a self-selected training pace. 3D kinematic data were collected after 5 minutes of running and again at the end of run at 200Hz using reflective markers placed on the lower body with 6 infrared cameras. Variables of interest included ankle, knee and hip sagittal and frontal plane angles. Standard deviation (SD) and coefficient of variation (CV) were calculated for each dependent variable (DV) at the beginning and end of the run. Approximate entropy (ApEn) was also calculated for each DV at both time intervals. Two repeated measures ANOVAs with time and joint as the within-subject factors and group as the between-subject factor, were used to compare kinematic variability. Post-hoc analyses were conducted for significant interactions. Alpha level was set at 0.05. RESULTS: Average running speed for the LM and HM group were 2.5±.3 m/s and 2.9±.4 m/s, respectively. In the sagittal plane, a significant interaction was found between joint and group (F2,62=5.5, p=.006). Specifically, the HM group demonstrated greater amounts of variability (SD) than the LM group (LM=25.7±3.0; HM=29.5±3.7). No other statistically significant differences were attained. CONCLUSIONS: Kinematic variability differed between the LM and HM groups, but only for the knee in the sagittal plane. Ankle and hip sagittal plane movement was comparable between the LM and HM groups. This may suggest that movement of the ankle and the hip do not differ in response to having to control variability at the knee. When assessing kinematic variability, it is important to consider the weekly mileage of each runner.