Probing Gait Adaptations: The Impact of Aging on Dynamic Stability and Reflex Control Under Varied Weight-Bearing Conditions

Maintaining stable walking patterns is essential for preserving health and well-being throughout the aging process. While several biomechanical models have been developed to describe adaptation and walking stability, the role of reflex control remains underexplored. This study aimed to understand the mechanisms by which disturbances to gait patterns (changes to weight-bearing conditions) are influencing gait adaptations, gait variability, and their underlying reflex control during treadmill walking in young and older adults. Twenty young (mean age 25.7±3.3 years) and 20 older adults (62.3±4.3 years) walked on a treadmill under five weight-bearing conditions: normal bodyweight, 20% and 40% additional weight (bodyweight loading), and 20% and 40% reduced weight (bodyweight unloading). Linear mixed-effects models were used to assess spatiotemporal gait parameters, margin of stability, gait variability (standard deviation), and H-reflex responses during stance phase. Bodyweight unloading significantly reduced antero-posterior margin of stability (p<0.01). Compared to young adults, older adults exhibited shorter stride length, longer double-limb support time, larger antero-posterior margin of stability, and increased variability (p<0.05). While H-reflex amplitudes increased with increasing weight-bearing in young adults, older adults were less capable to modulate their H-reflex amplitude across weight conditions. These findings suggest that gait adaptations under altered weight-bearing conditions involve shifts in temporal regulation and movement strategies. The reduced reflex modulation in older adults may indicate a limited ability to adapt spinal-level reflex responses, leading to greater reliance on other balance control mechanisms. Understanding these neuromuscular adaptations is essential for designing prevention programs to enhance stability and prevent falls.