Hypothesis
The symmetric steps people adopt when adapting to a split-belt treadmill are the energetically cheapest gait, consistent with the idea that the motor system minimises energy cost.
What failed
Across a range of imposed step asymmetries, equal step lengths minimised neither metabolic nor mechanical cost, and participants' perceived effort did not track asymmetry. Symmetry came out optimal only for a composite metric combining metabolic and mechanical cost.
Broken assumption
Locomotor adaptation converges on the gait that minimises metabolic energy expenditure.
Why
The authors suggest adaptation may optimise a combined estimate of effort derived from body-environment feedback rather than metabolic energy alone.
From the published paper: Sánchez et al. Scientific Reports, 2017. ↗CC BY