The Effect Of Soleus Functional Electrical Stimulation On Walking Biomechanics And Metabolism In Younger And Older Adults

Mobility is linked to older adults' overall health, independence, and quality of life. Unfortunately, walking performance tends to decline with advanced-age, as older adults expend more metabolic energy during walking compared to younger adults. Older adults produce less ankle extension and more hip extension during walking compared to younger adults, which may be a main contributor to the age-related increase in metabolic cost during walking. These changes in joint mechanics can be potentially reversed with the use of functional electrical stimulation (FES), since FES is able to enhance plantar flexion. We hypothesized that FES would increase ankle moment, reduce hip moment, and decrease metabolic cost during walking compared to walking without FES. PURPOSE: To determine whether stimulating calf muscles during walking will attenuate the age-related distal-to-proximal redistribution in joint mechanics and increased metabolic cost. METHODS: Ten healthy adults (5 younger: 21 ± 2 yrs; 5 older: 80 ± 6 yrs) participated in this study, walking on the treadmill at 1.25 m/s for familiarization, baseline, and FES trials. FES was triggered when the propulsive anterior-posterior ground reaction force was over 10% body weight. Metabolic cost was recorded at baseline and during FES trials. Maximal voluntary contraction and soleus FES-evoked ankle moments were measured using a dynamometer. A two-way repeated measures ANOVA (factors: FES and age) with Tukey’s post-hoc analysis was used to compare metabolic cost and joint kinematics. RESULTS: There was no difference between groups; however, ankle moments were higher during walking with FES (1.32 ± 0.24 Nm/kg) (1.29 ± 0.23 Nm/kg (p = 0.005). The metabolic cost did not significantly change between baseline and FES conditions (Baseline: 3.10 ± 0.56 W/kg, FES: 3.23 ± 0.59 W/kg, p = 0.17). CONCLUSIONS: FES may improve ankle moments, enabling the benefits of neuromuscular stimulation without the consequence of increased metabolism.