Initial contact and toe off event identification for rearfoot and non-rearfoot strike pattern treadmill running at different speeds.
The purpose of this study was to determine the validity of kinematic based initial contact (IC) and toe-off (TO) identification algorithms for rearfoot and non-rearfoot runners across a broad range of treadmill running speeds. 14 healthy active participants completed six 20-60 s treadmill running trials at 6 speeds: 2.24, 2.68, 3.13, 3.58, 4.02, and 4.48 ms-1. 3D kinematic data were collected for the last 20 s of each trial. Force plates (FP) were used as the gold standard to determine ICFP and TOFP for each step. Three algorithms for finding IC, ICMilner, ICAlvim, ICAlvim-mod, and one algorithm for finding toe off, TOFellin, were chosen for analysis. Root mean square errors (RMSE) and difference scores with 95% confidence intervals were computed for IC, TO and stance time (ST). ICAlvim RMSE ranged from 0.175 to 0.219 s. STAlvim RMSE ranged from 0.168 to 0.216 s. ICAlvim-mod RMSE ranged from 0.105 to 0.131 s. STAlvim-mod RMSE ranged from 0.108 to 0.129 s. ICMilner RMSE ranged 0.012 to 0.015 s. STMilner RMSE ranged 0.019 to 0.024 s. ICMilner accuracy was inversely related to speed. ICMilner corrected with a linear regression equation reduced differences to- 0.006 ± 0.012 s with 86% of foot strikes identified within 20 ms and 58% with 10 ms. TOFellin RMSE ranged from 0.012 to 0.016 s. ICMilner adjusted for speed and TOFellin can be used to predict IC and TO within a broad range of treadmill running speeds (2.24-4.48 ms-1) and for rearfoot and non-rearfoot strikers.