Abstract
Key points Goal‐directed arm movements can be adjusted at short latency to target shifts.We tested whether similar adjustments are present during walking on a treadmill with shifting stepping targets.Participants responded at short latency with an adequate gain to small shifts of the stepping targets.Movements of the feet during walking are controlled in a similar way to goal‐directed arm movements if balance is not violated. It is well‐known that goal‐directed hand movements can be adjusted to small changes in target location with a latency of about 100 ms. We tested whether people make similar fast adjustments when a target location for foot placement changes slightly as they walk over a flat surface. Participants walked at 3 km/h on a treadmill on which stepping stones were projected. The stones were 50 cm apart in the walking direction. Every 5–8 steps, a stepping stone was unexpectedly displaced by 2.5 cm in the medio‐lateral direction. The displacement took place during the first half of the swing phase. We found fast adjustments of the foot trajectory, with a latency of about 155 ms, initiated by changes in muscle activation 123 ms after the perturbation. The responses corrected for about 80% of the perturbation. We conclude that goal‐directed movements of the foot are controlled in a similar way to those of the hand, thus also giving very fast adjustments.
Highlights
The ability to adjust ongoing movements to new visual information has been studied extensively in goal-directed reaching
It is not clear whether similar adjustments are to be expected for the cyclic movements of the feet when walking over a flat surface, because when walking the feet are carefully placed in the medio-lateral direction to maintain balance (Donelan et al, 2004)
The variables describing the kinematics and centre of pressure (COP) that we report are signed: in the medio-lateral direction, positive is in the same direction as the perturbation; in the anterior-posterior direction, positive is in the walking direction
Summary
The ability to adjust ongoing movements to new visual information has been studied extensively in goal-directed reaching. While fast adjustments were reported for a reach-like stepping task (Reynolds & Day, 2005), for walking only the study by Weerdesteyn et al. To encourage fast responses of the foot, we will expose walking participants to small target shifts that pose little threat to the participants’ balance. Another related factor that might influence the presence of movement adjustments is the timing of the perturbation. The question we address is whether the leg muscle activation and the kinematics of the foot during walking can be adjusted with a latency that is clearly less than 200 ms in response to small changes in the position of stepping targets. Since these bilateral responses occur about synchronously, they seem to be part of a coordinated postural reaction rather than being an element of anticipatory postural adjustment
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