Tibiofemoral contact forces during walking with and without peak vertical ground reaction force feedback

The purpose of this study was to investigate whether individuals carrying vest-borne loads of 0%, 15%, and 30% body weight can decrease peak vertical ground reaction force (vGRF) when given peak vGRF feedback and examine if the gait adaptations induced by vGRF feedback decrease peak tibiofemoral joint (TFJ) contact force and impulse. Twenty-four participants walked without and with vGRF feedback at 1.4 m·s^-1 with 0%, 15%, and 30% load added. They received feedback on the average peak vGRF for each leg in two-second epochs during each of the six conditions. Participants significantly decreased the second peak vGRF and vGRF impulse with feedback, but not the first peak vGRF. Due to an adopted crouched pattern, participants increased both first and second peak TFJ contact forces. vGRF and TFJ contact forces increased directly with increased load in both feedback conditions. vGRF force feedback represents an intuitive tool for modifying walking mechanics, but when employed to decrease ground reaction forces during load carriage in this study, it did not lead to decreased TFJ contact forces. Participants adopted a crouched gait that involved increased knee flexion and subsequent quadriceps demand, ultimately elevating TFJ loading. Future strategies aimed at decreasing joint load should consider targeting primary contributors of joint load, such as knee extensor moments, quadriceps force, or joint contact forces directly.