Effect of cost gradient in the initiation of energy optimization during walking

People can continuously optimize their walking gait to reduce energetic cost. However, they do not always do so spontaneously. Here we tested the hypothesis that the cost gradient at the original optimum allows the nervous system to detect when the optimum has changed and thus re-optimize. Using a mechatronic system that manipulates people’s energetic cost as a function of their walking step frequency, we measured participants’ spontaneously preferred frequency in cost landscapes with gradients of 0.8% to 5.2% change in cost per unit change in frequency. We also measured their preferred frequency following a protocol previously validated to cause re-optimization in new landscapes. Surprisingly, we found no adaptation in any of our trials, suggesting that our method of changing landscapes might have inhibited the nervous system’s re-optimization rather than promote it.