Optical modulation of locomotion and energy expenditure at preferred transition speed.

The effect of optical flow on locomotion stability and efficiency was evaluated at preferred walk-run transition speed (PTS). Seven participants were instructed to locomote (walk or run) at PTS, while looking at the end of a three-dimensional virtual corridor projected on a large screen. Three experimental conditions of optical flow were tested: optical flow velocity consistent with locomotion speed (C), optical flow velocity twice faster (F) or slower (S) than locomotion speed. They were contrasted with a control static flow condition. Transitions between patterns were more frequent in (C) than in the other conditions, suggesting that optical flow influenced the stability of locomotion. Moreover, kinematic analyses revealed a stronger destabilization of gait in (F), accompanied by a decrease in energy expenditure in that condition. These results suggest that optical flow influenced both energetic and gait components at PTS, encouraging the exploration and stabilization of the most economic behavior. The mutual dependency of the visual system, the locomotor system and the cardio-respiratory system is emphasized.