Height of the intersection point of the ground reaction force vectors (zIP). Panel A: Time profiles of zIP across frequency bands. Averaged data across subjects are shown with standard error shades for the No-C and High-C conditions. Interval-1, Interval-2, and Interval-3 are defined as < 1.5 Hz, 1.5 – 3.0 Hz, and > 3.0 Hz.
Panel B: zIP for the No-C, Low-C, and High-C conditions. Averaged data across subjects are shown with standard error bars. Statistically significant differences are shown with one star (p < 0.05).
No-C -natural level of muscle activation; Low-C – low muscle co-activation level; and High-C – high muscle co-activation level.