Both a single sacral marker and the whole-body center of mass accurately estimate peak vertical ground reaction force in running.

Abstract Background While running, the human body absorbs repetitive shocks with every step. These shocks can be quantified by the peak vertical ground reaction force ( F v , m a x ). To measure so, using a force plate is the gold standard method (GSM), but not always at hand. In this case, a motion capture system might be an alternative if it accurately estimates F v , m a x . Research question The purpose of this study was to estimate F v , m a x based on motion capture data and validate the obtained estimates with force plate-based measures. Methods One hundred and fifteen runners participated at this study and ran at 9, 11, and 13 km/h. Force data (1000 Hz) and whole-body kinematics (200 Hz) were acquired with an instrumented treadmill and an optoelectronic system, respectively. The vertical ground reaction force was reconstructed from either the whole-body center of mass (COM-M) or sacral marker (SACR-M) accelerations, calculated as the second derivative of their respective positions, and further low-pass filtered using several cutoff frequencies (2−20 Hz) and a fourth-order Butterworth filter. Results The most accurate estimations of F v , m a x were obtained using 5 and 4 Hz cutoff frequencies for the filtering of COM and sacral marker accelerations, respectively. GSM, COM-M, and SACR-M were not significantly different at 11 km/h but were at 9 and 13 km/h. The comparison between GSM and COM-M or SACR-M for each speed depicted root mean square error (RMSE) smaller or equal to 0.17BW (≤6.5 %) and no systematic bias at 11 km/h but small systematic biases at 9 and 13 km/h (≤0.09 BW). COM-M gave systematic biases three times smaller than SACR-M and two times smaller RMSE. Significance The findings of this study support the use of either COM-M or SACR-M using data filtered at 5 and 4 Hz, respectively, to estimate F v , m a x during level treadmill runs at endurance speeds.