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 × 2 (speed × day) repeated measures ANOVA (α = 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.