Accurate estimation of peak vertical ground reaction force using the duty factor in level treadmill running.

This study aimed to 1) construct a statistical model (SMM) based on the duty factor (DF) to estimate the peak vertical ground reaction force (F <sub>v,max</sub> ) and 2) to compare the estimated F <sub>v,max</sub> to force plate gold standard (GSM). One hundred and fifteen runners ran at 9, 11, and 13km/h. Force (1000Hz) and kinematic (200Hz) data were acquired with an instrumented treadmill and an optoelectronic system, respectively, to assess force-plate and kinematic based DFs. SMM linearly relates F <sub>v,max</sub> to the inverse of DF because DF was analytically associated to the inverse of the average vertical force during ground contact time and the latter was very highly correlated to F <sub>v,max</sub> . No systematic bias and a 4% root mean square error (RMSE) were reported between GSM and SMM using force-plate based DF values when considering all running speeds together. Using kinematic based DF values, SMM reported a systematic but small bias (0.05BW) and a 5% RMSE when considering all running speeds together. These findings support the use of SMM to estimate F <sub>v,max</sub> during level treadmill runs at endurance speeds if underlying DF values are accurately measured