Comparison of an in-shoe pressure measurement device to a force plate: concurrent validity of center of pressure measurements.

The purpose of this study was to assess the concurrent validity of center of pressure (COP) measurements during walking, comparing the Parotec System (an in-shoe pressure measurement device) to an Advanced Mechanical Technology Inc. (AMTI) force plate. Pearson correlation coefficients comparing COP displacement in the medial-lateral (ML) and anterior-posterior (AP) direction calculated from the two systems were greater than 0.70 for 52/67 trials (78%) in the ML direction and were greater than 0.90 for 67/67 trials (100%) in the AP direction. The mean root mean square (RMS) error for COP displacement in the ML direction was 0.56+/-0.3 cm and in the AP direction was 1.37+/-0.59 cm. Overall, the Parotec System showed good correlation and small RMS errors when compared to the AMTI force plate. Additional analysis to investigate sources of error pointed to the methods used for calculating the position and orientation of the subject's foot on the force plate. Subsequent analysis to eliminate some of these errors, compared force calculated from the Parotec System and the AMTI plate and showed good to excellent correlation (>0.70) for 62/67 trials (93%). Additional data were collected that allowed for elimination of methodological errors. Again force calculated from the two systems was compared using Pearsons. These data showed excellent correlation (>0.90) for 20/20 trials (100%). This study provides evidence of the validity of the Parotec System for measuring COP during ambulation.