COMPARISON OF KINETIC AND KINEMATIC DATA COMMON TO INSOLE PRESSURE AND FORCEPLATE SYSTEMS

Abstract

Forceplates (FP) and insole pressure measurement (IPM) systems are commonly used in gait analysis; each provides unique data collection advantages, while reporting several common parameters. PURPOSE This study was conducted to compare the foot contact time (FCT), peak vertical force (PVF) and foot strike impulse (FSI) reported by FP and IPM systems. METHODS Data were simultaneously collected using a FP and an IPM for 36 walking trials of self-selected speed. Six healthy college aged adults acted as subjects and performed a series of six trials; each was analyzed related to FCT, PVF, and FSI. Subjects with narrow feet were tested using insoles with 16 sensors per sole (IPM16) while subjects with normal to wide feet were tested using 24 sensor insoles (IPM24). All IPM data were collected at its maximum rate of 250Hz/sensor with FP data collected at 6000Hz. RESULTS 18 IPM24 and 14 IPM16 trials yielded acceptable data for analysis. ANOVAs were run which indicated significant differences (P < 0.05) between all FP and IPM data regardless of sensor density. For the parameters FCT, PVF and FSI analysis indicated that FP data averaged 3.1, 256.8, and 256.3% greater when compared to IPM16 data and 8.6, 28.5, and 26.0% greater than IPM24 data. Visual comparison of the force vs. time curves for both FP vs. IPM16 and IPM24 data revealed very similar curves with the magnitudes of the IPM16 data appearing markedly lower. CONCLUSIONS Increased plantar surface coverage with the IPM24 sensor insoles provided much closer PVF and FSI values to the FP data than IPM16 insoles. Most of the FCT variation between the FP and the IPM data results from differences in collection frequencies and IPM data collection beginning when a threshold of 2.5N/cm2 is met. Due to the physical properties of the insoles and shoes worn during testing, in-shoe forces were attenuated which coupled with the limited surface area coverage provided by the insoles explains the differences in PVF and IMP values. The causes of variations between FP and IPM output must be understood by those using them for gait analysis.