Effects of body weight support and walking speed on device-derived hip angles and muscle activity symmetry during overground robotic-assisted walking in older adults

Understanding how body weight support (BWS) and walking speed influence gait in older adults may help guide the selection of assistance settings during robotic-assisted gait rehabilitation. These parameters are routinely adjusted during clinical practice, yet their effects during overground robotic-assisted walking remain insufficiently characterized. This study investigated how different levels of BWS and walking speed were associated with device-derived hip angles and bilateral muscle activity symmetry in older adults. Thirteen older adults (85.4 ± 6.8 years) completed overground walking trials using a robotic-assisted BWS system under nine experimental conditions combining three BWS levels (0%, 25%, and 50%) and three walking speeds (0.058, 0.225, and 0.400 m/s). Device-derived peak hip flexion and extension angles and bilateral muscle activity symmetry of the medial gastrocnemius and tibialis anterior were analyzed. Separate two-way repeated-measures ANOVA models were used to evaluate the effects of walking speed and BWS on each outcome. Increasing BWS reduced device-derived peak hip flexion and the magnitude of peak hip extension. Compared with 0% BWS, 50% BWS reduced peak hip flexion by 4.87° (95% CI, 2.87 to 6.86; p < 0.001) and reduced hip extension by 1.91° (95% CI, 1.30 to 2.51; p < 0.001). Walking speed also significantly affected peak hip extension ( p = 0.036), with greater peak hip extension at high than at low speed (mean difference, 0.72°; 95% CI, 0.25 to 1.19; Holm-adjusted p = 0.019). Medial gastrocnemius symmetry was significantly affected by walking speed ( p = 0.022), with lower symmetry at high than at low and medium speeds. Tibialis anterior symmetry showed a significant walking speed × BWS interaction ( p = 0.049), although no pairwise comparison remained significant after Holm adjustment. BWS and walking speed were associated with changes in device-derived hip angles and bilateral muscle activity symmetry during overground robotic-assisted walking in older adults. The observed responses differed across outcomes and muscles. These exploratory findings may help inform future studies examining how assistance parameters influence gait during robotic-assisted rehabilitation. This investigation was retrospectively registered at ClinicalTrials.gov (NCT06025981; first posted September 6, 2023).