Effects of Center of Pressure Processing on Gait Biomechanics in People With Chronic Ankle Instability: A Technical Report.

CONTEXT: Chronic ankle instability is associated with persistent biomechanical changes including a lateral center of pressure (COP) location during stance. Gait retraining studies generally show COP location improvements. Multiple COP processing techniques are available which may impact results. Therefore, the purpose of this study is to identify the impact of processing technique on the COP location during baseline walking and in response to intervention in people with chronic ankle instability. DESIGN: Cohort Study. METHODS: Participants with chronic ankle instability walked on an instrumented treadmill for 2 minutes (baseline), completed a vibration feedback gait retraining session, and then completed a posttest treadmill trial with no feedback. The COP location was filtered using a fourth-order Butterworth filter with a 10-Hz low-pass cutoff. Processing techniques included bounding COP data within the foot: (1) relative to the border of the lateral foot in the medial-lateral plane (Straight-Plane Technique) and (2) relative to the midline of the foot which changes with foot progression angle (Foot-Progression-Angle Technique). 1D statistical parametric mapping paired t tests were completed on absolute change scores at baseline between techniques and between baseline and posttest for each of the techniques. RESULTS: Absolute COP change scores at baseline between processing techniques were statistically different from 5% to 44% of stance phase while walking. Baseline to posttest COP locations were statistically different from 4% to 62% of stance phase (P ≤ .01) when processed with the Straight-Plane Technique. No statistically significant difference was identified using the Foot-Progression-Angle Technique. CONCLUSIONS: Interpretations of COP location and COP location changes could be impacted by processing techniques with differing reference coordinate systems. New insights into processing techniques could impact interpretations of previously published work and should be considered before comparing across studies to make broad generalizations related to the COP location.