Altered Vertical Ground Reaction Forces in Participants With Chronic Ankle Instability While Running.

CONTEXT: Altered gait kinetics may increase the risk of long-term injuries in participants with chronic ankle instability (CAI). Vertical ground reaction forces (vGRFs) can provide insight into how body loading is altered.

OBJECTIVE: To compare the components of vGRFs while running in participants with or without CAI.

DESIGN: Cohort study.

SETTING: University biomechanics laboratory.

PATIENTS OR OTHER PARTICIPANTS: Twenty-four experienced, college-aged runners. Groups were categorized by the presence (CAI group) or absence (control group) of CAI through self-reported questionnaires.

INTERVENTION(S): After a warm-up period, all participants ran on an instrumented treadmill for 5 minutes at 3.3 m/s. Data were collected during the last 30 seconds. Five continuous trials of heel-to-toe running were identified per participant and averaged for statistical analysis.

MAIN OUTCOME MEASURE(S): The dependent variables were impact peak force (N/body weight [BW]), active peak force (N/BW), time to impact peak force (milliseconds), time to active peak force (milliseconds), and average loading rate ([N/BW]/s).

RESULTS: A difference was found between groups (P = .002). The CAI group had higher impact peak forces (P = .001) and active peak forces (P = .002) compared with the control group. The CAI group also had an increased loading rate (P = .001) and a shorter time to reach the active peak force (P = .001) compared with the control group. No difference was seen between groups in the time to reach the impact peak force (P = .952).

CONCLUSIONS: Participants with CAI produced altered vGRFs and loading rates while running. Altered loading rates could predispose individuals with CAI to stress-related injuries and repetitive sprains.