Predicting Ground Reaction Force from a Hip-Borne Accelerometer during Load Carriage

Abstract

Introduction Ground reaction forces (GRF) during load carriage differ from unloaded walking. Methods to quantify peak vertical GRF (pGRF_vert) of Soldiers walking with loads outside of a laboratory are needed to study GRF during operationally relevant tasks. Purpose Develop a statistically based model to predict pGRF_vert during loaded walking from ActiGraph GT3X+ activity monitor (AM) vertical acceleration. Methods Fifteen male Soldiers (25.4 ± 5.3 yr, 85.8 ± 9.2 kg, 1.79 ± 9.3 m) wore an ActiGraph GT3X+ AM over their right hip. Six walking trials (0.67–1.58 m·s⁻¹) with four loads (no load, 15, 27, 46 kg) and two types of footwear (athletic shoes and combat boots) were completed on an instrumented force plate treadmill. Average peak vertical AM acceleration (pACC_vert) and pGRF_vert were used to develop a regression equation to predict pGRF_vert. The model was validated using a leave-one-subject-out approach. Root mean square error (RMSE) and average absolute percent difference (AAPD) between actual and predicted pGRF_vert were determined. pGRF_vert was also predicted for two novel data sets and AAPD and RMSE calculated. Results The final equation to predict pGRF_vert included pACC_vert, body mass, carried load mass, and pACC_vert-carried load mass interaction. Cross-validation resulted in an AAPD of 4.0% ± 2.7% and an RMSE of 69.5 N for leave-one-subject-out and an AAPD of 5.5% ± 3.9% and an RMSE of 78.7 N for the two novel data sets. Conclusion A statistically based equation developed to predict pGRF_vert from ActiGraph GT3X+ AM acceleration proved to be accurate to within 4% for Soldiers carrying loads while walking. This equation provides a means to predict GRF without a force plate.