Functional Electrical Stimulation of the Plantarflexor Muscle During Walking Leads to a Proximal-to-Distal Redistribution of Lower Limb Joint Work.

Objective: This study aimed to compare the effects of different conditions of functional electrical stimulation (FES) applied to the ankle plantarflexor muscles (gastrocnemius, soleus, or both combined) during push-off on lower limb joint biomechanics at controlled walking speeds in healthy young adults.

Methods: Fifteen healthy young adults walked along a 7-meter walkway at controlled speeds under six conditions: bilateral stimulation of the soleus, gastrocnemius, both muscles combined, and matched-speed trials without stimulation. Stimulation was applied below the discomfort threshold during push-off (heel-off to toe-off of the trailing leg). Two force plates and a motion capture system measured lower limb joint biomechanics.

Results: All FES conditions increased positive (+8%) and total mechanical work (+5%) at the ankle. FES reduced positive knee work (- 10%) and negative hip work (- 5%), although this was significant only for gastrocnemius stimulation alone or combined with soleus. The ankle's contribution to both positive and total lower limb work increased with FES, while the contributions of the knee and hip decreased regardless of the stimulation condition. Additionally, FES increased ankle plantarflexion angle (13%) and velocity peaks (6%), without affecting spatiotemporal gait parameters at comparable speeds.

Conclusion: FES applied to the plantarflexor muscles during push-off leads to a proximal-to-distal redistribution of lower limb joint work during walking at controlled speeds in healthy young adults, with subtle differences depending on the stimulation condition. These findings underscore the potential of FES as a solution to redistribute lower limb joint work during walking.