Reliability Of Lower Extremity Kinetics And Kinematics For Constrained And Self-selected Running Speeds

Abstract

Previous running research has indicated that alterations in running gait occur as running speeds increase. The importance of standardizing running speed, therefore, has been debated within the literature. Some investigators have suggested that running speed should be standardized for all subjects, while others believe that running speed should be self-selected by subjects and then maintained as constant for each subject throughout all testing. No investigations, however, have examined the effects of constrained and self-selected running speeds on the reliability of running kinematics and kinetics. PURPOSE To determine the effect of self-selected versus constrained running speeds on within-day and between-day reliability of lower extremity kinematics and kinetics. METHODS Kinematic and kinetic data were collected for recreational athletes (6 female, 6 male, age 18–35) with no lower extremity injuries, while subjects ran over ground. Kinematic data were collected using a real time three-dimensional motion analysis system (Peak Performance) collecting at 120Hz, while the ground reaction forces (GRF) were collected at 1200Hz. The reliability of peak values for three-dimensional knee and ankle kinematics, moments, and ground reaction forces were analyzed using the coefficient of variation. In addition, three-dimensional ankle and knee kinematics, moments, angular velocity, and GRF for the entire stance phase were analyzed using the coefficient of multiple correlation (CMC). Each variable was analyzed using a 2×2×2 (speed × group × day) repeated measures ANOVA (X=0.05). RESULTS No significant difference in reliability existed between days for self-selected running speed. The reliability for impact peak of the vertical GRF and the anterior-posterior GRF were significantly better for the constrained speed than the self-selected speed. Ten of the 20 kinetic and kinematic CV analyses and 11 of the 15 kinetic and kinematic CMC analyses demonstrated better within-day reliability than between-day reliability. CONCLUSIONS Within-day reliability is generally better than between-day reliability. Running speed had little effect on the reliability of any study variable. Having subjects run at a constrained speed may not be as important as previously thought. The effects of self-selected and constrained running speed, however, must still be identified for kinematic and kinetic variables.