The Effects of Orthotics on Lower Extremity Kinematic Variability During Running

Abstract

Abnormal foot mechanics during running may affect the kinematics of the lower extremities and predispose individuals to injuries of the foot, ankle, and knee. Orthotics are often used to correct these abnormal gait mechanics. Since previous research indicates that changes invariability may be related to running injuries (Hamill et al., 1999), understanding the effects of orthotics on movement variability of the lower extremities may be useful for injury prevention. PURPOSE: To examine the effects of an orthotic on lower extremity kinematic variability during running. METHODS: Thirty male and female runners identified as being excessive pronators participated in this study. Subjects were required to perform two testing sessions in which they ran with and without orthotics; all subjects used the same model of orthotic and running shoe. During both testing sessions, the subjects ran on a treadmill at a velocity of 3.35 m/s for 15 min. A motion capture system was used to record the position of light emitting diodes placed on the foot, shank, and thigh segments at 100 Hz for 50 complete gait cycles during the last 5 min of each testing session. Range of motion (ROM), peak angular velocity (PAV), and peak angular acceleration (PAA) for the ankle and knee joints were calculated for the frontal, sagittal, and transverse planes of motion according to the methods outlined by Eng and Pierrynowski (1994). Variability was quantified as the intra-subject standard deviation for ROM, PAV, and PAA. A two-way analysis of variance was used to assess the effects of orthotics on ROM, PAV, and PA A variability. RESUITS: It was found that orthotics lead to significant increases in variability for ankle joint ROM in the transverse plane (from 9.6±1.4° to 12.0±2.7°; p<0.001), knee joint ROM in the transverse plane (from 8.4±1.3° to 9.6±2.1°; p<0.01), knee joint ROM in the frontal plane (from 7.6±1.6 to 9.2±2.3°; p<0.05), and knee joint PAV in the sagittal plane (from 438.6±33. 1°/s to 429.0±41.9°/s; p<0.05). While there was not a significant difference in ankle joint eversion ROM in the frontal plane when using orthotics, there was a strong trend towards increased variability (from 13.1±1.6° to 14.1±1.9°). CONCLUSIONS: Orthotics are commonly used to correct abnormal gait mechanics. However, this study demonstrates that orthotics can increase the variability of lower extremity kinematics during running; this increase in variability may predispose individuals to injury. Further research is necessary to determine the relationship between lower extremity kinematic variability and running injuries. This investigation was supported by a grant from the Mid-America Athletic Trainers Association.