Variability in Center of Pressure Position and Muscle Activation During Walking with Chronic Ankle Instability

Abstract

Chronic ankle instability (CAI) is a condition resulting in altered gait mechanics which may lead to recurrent ankle sprains. The role of stride-to-stride variability in gait mechanics in CAI patients is not yet understood. PURPOSE: To identify stride-to-stride variability differences in center of pressure position and muscle activation during walking between individuals with and without CAI. METHODS: Participants (17 CAI; 17 healthy) walked on a treadmill at 3.0mph while surface electromyography (sEMG) and plantar pressure were recorded. For plantar pressure, the medial-lateral location of center of pressure (COP) was measured during stance. The average location of COP during each 10% interval of stance was condensed to a discrete variable representing each 10% interval. Surface electromyography (EMG) root mean square (RMS) amplitudes throughout the entire stride cycle for the peroneus longus was collected and normalized to quiet standing. Independent t-tests were used to compare group standard deviations (SD), coefficient of variation (COV), and range for the location of COP. The 95% confidence intervals (CI) for each group were graphed for sEMG amplitude throughout the stride cycle. Areas where CIs did not cross were considered to be significant. RESULTS: The CAI group demonstrated a more variable location of COP as estimated by the SD (CAI=.79±.47 mm, Control=.48±.17 mm, P=.02) and COV (CAI=1.47±.87 mm, Control=.93±.33 mm, P=.03) and range (CAI=2.97±2.07 mm, Control=1.72±.33, P=.03) during the first 10% of stance but not during the last 90% of stance. The CAI group had lower peroneus longus RMS amplitude variability from 1-10% (mean difference = .014±.006), 32-38% (mean difference = .013±.004) and 56-100% (mean difference = .026+.01) of the stride cycle. CONCLUSION: During the first 10% of stance, the CAI group demonstrated a more variable location of COP indicating poor coordination just after initial contact. This may be problematic because individuals with CAI demonstrate a more laterally deviated COP than healthy individuals. For sEMG, the CAI group demonstrated less variability during entire swing phase through the first 10% of the gait cycle for the peroneus longus.