Motor adaptation of gait to bilaterally added lower-limb mass in young adults

Walking with bilaterally added lower-limb mass is a promising approach to improve gait function, but it alters the mechanics of the lower limbs. Consequently, the central nervous system needs to adapt and presumably form an internal model of the altered condition. However, this motor adaptation and de-adaptation process may jeopardize safe walking. This study aimed to analyze motor adaptation and de-adaptation in response to bilaterally added lower-limb mass.

Sixteen healthy female and male participants walked on a treadmill with and without weight cuffs attached to their thighs and shanks while full-body kinematics were recorded. Motor adaptation and de-adaptation were analyzed using discrete spatiotemporal (e.g., stride length, cadence, joint range of motion), local hip and trunk (maximum Lyapunov exponent), and global stability metrics (detrended fluctuation analysis of stride time).

Only minimum toe clearance showed a motor adaptation pattern, i.e., differed at the beginning of the adaptation and de-adaptation phases (both 0.023 ± 0.006% leg length) compared to baseline (0.016 ± 0.006% leg length; p < 0.001), and then converged close to baseline over multiple strides. Local hip stability was reduced during adaptation (baseline: 1.43 ± 0.42, adaptation: 1.64 ± 0.61; p = 0.017), while local trunk (baseline: 1.57 ± 0.45, adaptation: 1.69 ± 0.56; p = 0.301) and global stability did not differ from baseline (baseline: 0.74 ± 0.12, adaptation: 0.71 ± 0.12; p = 0.278).

The results are consistent with the idea that the central nervous system rapidly selects an established walking pattern that accommodates bilaterally added lower-limb mass, suggesting a potential prioritization of safe walking.