Estimating Propulsion Kinetics in Absence of a Direct Measurement of the Anterior Component of Ground Reaction Force

Anterior ground reaction force (AGRF) is a common measurement of propulsion mechanics. It is typically measured using multi-axis force-plates which are not always found in robotic research labs. Here we present a comparison of models using kinematic and kinetic metrics of propulsion to estimate AGRF. Nine models using measurements of maximum vertical ground reaction force (maxVGRF), vertical ground reaction force at peak AGRF (aVGRF), maximum trailing limb angle (maxTLA), trailing limb angle at peak AGRF (aTLA) and stride length (SL) were used to predict different metrics of propulsion kinetics, including maximum AGRF (maxAGRF), propulsive impulse (PI), maximum AGRF normalized by body-weight (maxAGRFnorm), and normalized PI (PInorm) from participants walking at speeds [0.6 1.4] m/s. R2 and AICc scores were recorded for each model, and the individual participant R²values for the best single and two-factor models for each outcome were examined. Of the single-factor models, kinematic measurements were the best predictors of the outcome measurements. More specifically, maxAGRF/norm were best predicted by SL (R² = 0.91, 0.82, respectively), and PI/norm were best predicted by maxTLA (R² = 0.84, 0.43, respectively). For the two-factor models, maxAGRFnorm and PInorm were both best predicted by SL and aVGRFnorm, and maxVGRF yielded the best predictions for maxAGRF and PI. Models predicting maxAGRF /norm better fit individual participants than those predicting PI/norm. These results indicate that maxAGRF can be estimated with reasonable accuracy (R² = 0.92, RMSE of residuals: 1.5% bodyweight, equivalent to a 0.09 m/s increase in velocity) in the absence of a direct measurement of AGRF using both kinematic and kinetic measurements of propulsion.