Ankle muscles drive mediolateral center of pressure control to ensure stable steady state gait

Abstract

During steady-state walking mediolateral gait stability can be maintained by controlling the center of pressure (CoP). The CoP modulates the moment of the ground reaction force, which brakes and reverses movement of the center of mass (CoM) towards the lateral border of the base of support. In addition to foot placement, ankle moments serve to control the CoP. We hypothesized that, during steady-state walking, single stance ankle moments establish a CoP shift to correct for errors in foot placement. We expected ankle muscle activity to be associated with this complementary CoP shift. During treadmill walking, full-body kinematics, ground reaction forces and electromyography were recorded in thirty healthy participants. We found a negative relationship between preceding foot placement error and CoP displacement during single stance. Too medial steps were compensated for by a lateral CoP shift and vice versa, too lateral steps were compensated for by a medial CoP shift. Peroneus longus, soleus and tibialis anterior activity correlated with these CoP shifts. As such, we identified an (active) ankle strategy during steady-state walking. As expected, absolute explained CoP variance by foot placement error decreased when walking with shoes constraining ankle moments. Yet, contrary to our expectations that ankle moment control would compensate for constrained foot placement, the absolute explained CoP variance by foot placement error did not increase when foot placement was constrained. We argue that this lack of compensation reflects the interdependent nature of ankle moment and foot placement control. We suggest that single stance ankle moments do not only compensate for preceding foot placement errors, but also assist control of the subsequent foot placement. Foot placement and ankle moment control are caught in a circular relationship, in which constraints imposed on one will also influence the other.

The effect of constraining mediolateral ankle moments and foot placement on the use of the counter-rotation mechanism during walking

“…The main mechanism for active control in the frontal plane has been suggested to be foot placement, with a smaller role for the ankle mechanism (Bauby and Kuo, 2000, MacKinnon and Winter, 1993, van Leeuwen et al, 2021. Theoretically, the counter-rotation mechanism may also play a role, but research on the role of the counter-rotation mechanism is limited.…”

“…When aiming to improve gait stability, it is important to unravel the use of the CoP and counter-rotation mechanisms and their interplay. Simply studying unconstrained walking may not be sufficient, as during normal walking, the foot placement mechanism is the dominant mechanism (Bauby and Kuo, 2000, MacKinnon and Winter, 1993, van Leeuwen et al, 2021. Constrained or perturbed walking might provide insight in the use of the CoP and counter-rotation mechanisms and their interplay.…”

Effects of vestibular stimulation on gait stability when walking at different step widths

“…However, it should be kept in mind that foot placement is only one mechanism by which stability can be controlled. Other mechanisms include the control of the center of pressure (Reimann et al 2018;van Leeuwen et al 2021), and angular momentum control (Hof 2008). Hence, it may well be that the improved foot placement control during walking with EVS was negated by a decrease in other control mechanisms, leading to a net reduction in gait stability.…”

“…However, such a decrease in stance leg control would most likely also result in a decrease in foot placement control (van Leeuwen et al 2021), and hence, isn't the most likely explanation. Moreover, EVS was previously shown to affect foot placement during gait initiation (Reimann et al 2017).…”

The effect of external lateral stabilization on energy cost of walking – A systematic review and meta-analysis

“…Firstly, the difference in energy cost of (nonstabilized) walking at zero and preferred step width (2.55 vs. 2.49 J kg -1 m -1 ) could be due to the use of different stabilizing strategies in these two walking patterns. For walking at preferred step width, foot placement is the main mechanism to control medio-lateral stability [16,17], while in walking at zero step width, foot placement is constrained and other stabilizing strategies, such as an ankle strategy [24,25] will be needed. The energy cost of the foot placement is expected to be low, as it needs small modifications in the trajectory of the swing leg only, whereas other strategies involve adaptations of the trajectory of the whole-body mass.…”