Figure 1.

The participant’s center of mass (COM, solid blue line) displacement during the balance response in quiet standing with backward perturbation of a representative participant. (A) COM displacement before the training; (B) COM displacement after the training. The reaction phase (yellow shaded area) is defined as the time between the COM movement onset (red solid line) and treadmill movement offset (black dot line). The recovery phase (green shaded area) is defined as the time from the treadmill movement offset (black dot line) to 0.5 s after the treadmill movement offset (pink dash line). Note that there were two peaks for COM displacement during the reaction phase before training (A), while there was only one peak during the reaction phase after training (B). The two peaks of COM displacement might indicate the participant moved around their body to maintain their balance. Therefore, the variance of COM displacement was calculated to quantify both the amplitude and the variability of the COM movement.