Effects of Functional Electrical Stimulation on Gait Characteristics in Healthy Individuals: A Systematic Review

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.

Société de Biomécanique young investigator award 2022: Effects of applying functional electrical stimulation to ankle plantarflexor muscles on forward propulsion during walking in young healthy adults

The triceps surae muscle, composed of the gastrocnemius and soleus muscles, plays a major role in forward propulsion during walking. By generating positive ankle power during the push-off phase, these muscles produce the propulsive force required for forward progression. This study aimed to test the hypothesis that applying functional electrical stimulation (FES) to these muscles (soleus, gastrocnemius or the combination of the two) during the push-off phase would increase the ankle power generation and, consequently, enhance forward propulsion during walking in able-bodied adults. Fifteen young adults walked at their self-selected speed under four conditions: no stimulation, with bilateral stimulation of the soleus, gastrocnemius, and both muscles simultaneously. Muscles were stimulated just below the discomfort threshold during push-off, i.e., from heel-off to toe-off. FES significantly increased ankle power (+22 to 28 % depending on conditions), propulsive force (+15 to 18 %) and forward progression parameters such as walking speed (+14 to 20 %). Furthermore, walking speed was significantly higher (+5%) for combined soleus and gastrocnemius stimulation compared with gastrocnemius stimulation alone, with no further effect on other gait parameters. In conclusion, our results demonstrate that applying FES to the gastrocnemius and soleus, separately or simultaneously during the push-off phase, enhanced ankle power generation and, consequently, forward propulsion during walking in able-bodied adults. Combined stimulation of the soleus and gastrocnemius provided the greatest walking speed enhancement, without affecting other propulsion parameters. These findings could be useful for designing FES-based solutions for improving gait in healthy people with propulsion impairment, such as the elderly.