ALTERED VERTICAL GROUND REACTION FORCES FOUND IN PARTICIPANTS WITH CHRONIC ANKLE INSTABILITY DURING RUNNING

Abstract

Altered gait kinematics and kinetics have been examined in subjects with chronic ankle instability (CAI). Altered vertical ground reaction forces (GRF) have been found in individuals with CAI compared to control subjects, in different movement patterns but not running. Running is a common component of numerous sporting events where ankle sprains occur. The purpose of this investigation was to determine if subjects with CAI produced altered vertical GRF compared to uninjured subjects while running. Specifically, we examined if differences existed in impact peak forces, time to the impact peak force, active peak forces, time to the active peak force and average loading rate between groups. Twenty-four subjects with previous running experience were recruited from a Midwestern community. Subjects were determined to have CAI if they met the following criteria: (1) a history of at least one self-reported lateral ankle sprain that occurred 12 months prior to study enrollment, (2) a history of recurrent sprains or feelings of “giving way” during functional activity, (3) a score of 11 or higher on the Identification of Functional Ankle Instability (IdFAI) Questionnaire. Control subjects had no history of lateral ankle sprains. All subjects were required to be active runners and rear foot strikers. Also, subjects had no previous lower extremity injuries in the last three months besides a lateral ankle sprain for the CAI group. All subjects had no history of fractures or surgeries to the lower extremities. Active runners were defined as consistently running for the past year, running at least three times per week and averaging a minimum of twenty miles per week. Testing took place on an instrumented treadmill. Each subject was given an opportunity to complete his or her pre-run stretching routine following a five minute warm-up and before the testing trial. During the testing trial, subjects ran at a standardized speed trial of 3.3 ms-1 for five minutes. Data was collected during the last 30 seconds of the trial period at 1200 Hz. Five consecutive GRF curves of the test ankle from the last 15 seconds of the data were identified and processed with a fourth order Butterworth filter and a custom written formula in R program to identify the dependent variables. A total of 13 control subjects and 11 subjects with CAI were included for statistical analysis. We found that subjects with CAI produced significantly higher impact peak forces, active peak forces, average loading rate and a shorter time to the active peak force compared to controls. No significant difference was found in the time to impact peak force between groups. The results of this study indicated that individuals with CAI produced altered kinetic variables compared to control subjects. Improper foot position at heel strike and strength deficits in the tibialis anterior could increase the impact peak force by striking the ground harder. Increased loading rates found in individuals with CAI could predispose individuals to lower extremity stress fractures and long-term complications such as osteoarthritis of the ankle joint. Overall, results of the study found that individuals with subjects with CAI produce altered GRFs than uninjured subjects while running.