The Effects of Stimulating Lower Leg Muscles on the Mechanical Work and Metabolic Response in Functional Electrically Stimulated Pedaling

Functional electrical stimulation (FES) pedaling with the muscles of the upper leg has been shown to provide benefit to spinal cord injured (SCI) individuals. FES pedaling with electrical stimulation timing patterns that minimize the stress-time integral of activated muscles has been shown to increase the work individuals can perform during the exercise compared to existing FES stimulation timing patterns. Activation of the lower leg muscles could further enhance the benefit of FES pedaling by increasing the metabolic response to the exercise. For SCI individuals, the objectives of this study were to experimentally determine whether FES pedaling with the upper and lower leg muscles would affect the work generated and increase the physiological responses compared to pedaling with the upper leg muscles alone. Work, rate of oxygen consumption ( V̇O
₂
), and blood lactate data were measured from nine SCI subjects (injury level T4-T12) as they pedaled using upper leg and upper and lower leg muscle groups on repeated trials. The subjects performed 6% more work with the upper and lower legs than with the upper legs alone, but the difference was not significant (p = 0.2433). The average rate of oxygen consumption associated with the upper leg muscles (441 ± 231 mL/) was not significantly different from the corresponding average for the upper and lower legs (473 ± 213 mL/) (p = 0.1176). The blood lactate concentration associated with the upper leg muscles (5.9 ± 2.3 mmoles/L) was significantly lower than the corresponding average for the upper and lower legs (6.8 ± 2.3 mmoles/L) (p = 0.0049). The results indicate that electrical stimulation timing patterns that incorporate the lower leg muscles do increase the blood lactate concentrations. However, there was not enough evidence to reject the null hypothesis that stimulating the lower leg muscles affected the work accomplished or increased the rate of oxygen consumption. In conclusion, incorporating the lower leg muscles in the exercise does not lead to negative effects and could result in enhanced exercise outcomes in the long term.