The Significance of Uneven Walking Transitory Modulations in Walking Momentum Regulation and Active Work

Uneven walking presents challenges such as balance maintenance and increased energetics. Beyond average step parameter variations, humans may employ transient strategies to conserve mechanical work or enhance momentum with minimal metabolic costs. Thus, we quantified mid-flight positive mechanical work induction, step length, and effective leg length modulation from four steps before to four steps after a specific encounter for young and older adults with normal and restricted lookaheads. Simulations were also conducted to assess the impact of step length or effective leg length changes on step-to-step transition or post-transition speed. We observed that young adults mid-flight energy inducements were focused around the encounter, influenced by lookahead state affecting modulation based on feedback or feedforward control. While with the restricted lookahead, older adults showed similar regulation, their anticipatory modulation was poorer and extended over the evaluation interval. With normal lookahead, young adults reduced step length just before the encounter, potentially increasing momentum with less heel-strike energy dissipation. Step length changes around and after the perturbation may have been passive. Older adults exhibited longer modulation periods than young adults. We also noted active leg length modulation, likely influenced by tactile sensory information. For up-steps, effective leg lengths were shorter, while for down-steps, they were longer, potentially compensatory actions to minimize COM vertical fluctuations and associated work against gravity. The amplitude of leg length modulation may have been constrained by the flexed legs walking energetic cost or and ankle range of motion. With restricted lookahead, older adults showed larger leg length modulation amplitudes.