Fast responses to stepping‐target displacements when walking

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. ABSTRACT: 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.