Repeatability of lower extremity kinetics and kinematics for standardized and self-selected running speeds.

INTRODUCTION: The purpose of this study was to determine the effects of self-selected versus standardized running speeds on within-day and between-day repeatability of lower extremity kinematics and kinetics for running gait.
METHODS: Subjects (six female, six male, age 18-35) were recreational athletes with no lower extremity injuries. The following study variables were analyzed using the coefficient of variation (CV): the peak angles for knee internal rotation, external rotation, varus, valgus, flexion, and extension; peak angles for ankle dorsiflexion and plantar flexion; peak impact force and propulsive force; and peak anterior, posterior, medial, and lateral ground reaction forces (GRFs). Data for the entire stance phase were analyzed using the coefficient of multiple correlation (CMC) for the following variables: anterior-posterior, medial-lateral, and vertical GRF; the angles and angular velocities for knee internal-external rotation, valgus-varus, flexion-extension, and ankle dorsiflexion-plantar flexion. Each variable was analyzed using a 2 x 2 (speed x day) repeated measures ANOVA (alpha = 0.05).
RESULTS: The within-day repeatability for all of the significantly different variables was greater than the between-day repeatability. For variables with a significant difference based on speed, the standardized running speed had greater repeatability.
CONCLUSIONS: Within-day repeatability is generally greater than between-day repeatability. Running speed had little effect on the repeatability of any study variable. Having subjects run at a standardized speed may not be as important as previously thought.