Humans exploit robust locomotion by improving the stability of control signals

Is the control of movement less stable when we walk or run in challenging settings? One might intuitively answer affirmatively, given that adding constraints to locomotion (e.g. rough terrain, age-related impairments, etc.) imply less stable movements. We investigated how young and old humans synergistically activate muscles during locomotion, when different perturbation levels are introduced. Of these control signals, called muscle synergies, we then analyzed the stability over time. Surprisingly, we found that perturbations and older age force the central nervous system to produce more stable signals. These outcomes show that robust locomotion in challenging settings is achieved by increasing the stability of control signals, whereas easier tasks allow for more unstable control.