Contribution of Tibialis Anterior in Sit-to-Stand Motion: Implications for Its Role in Shifting the Center of Pressure Backward

<b>Background:</b> The role of tibialis anterior activity in sit-to-stand motion is unclear. We hypothesized that contraction of the tibialis anterior would slightly lift the forefoot and shift the center of pressure backward. <b>Objectives:</b> The objective of this study was to clarify this movement and its role in tibialis anterior activity. <b>Methods:</b> Ten healthy adults performed the sit-to-stand motion. Cross-correlation coefficients among tibialis anterior activity, shank inclination angle, and center of pressure were calculated. Whole-body joint moments were simulated when the center of pressure varied within the foot. The angle of the ground reaction force during seat-off was calculated. <b>Results:</b> The center of pressure moved backward in all trials for all participants. The mean lag time for peak cross-correlation coefficients between the tibialis anterior and shank tilt and between the tibialis anterior and center of pressure was 0.37 and 0.13 s, respectively. Simulating the center of pressure forward resulted in greater whole-body joint moments than those measured (mean 1.88 times). The ground reaction forces were nearly perpendicular to the floor. <b>Conclusions:</b> From the perspective of temporal synchrony, tibialis anterior activity significantly contributed to the backward shift of the center of pressure. The center of pressure shift minimized the force exerted by the entire body.