Does decreased motor axon excitability contribute to contraction fatigability during functional electrical stimulation?

Axons hyperpolarise when they transmit trains of action potentials. Presently, we explored the link between the hyperpolarisation of motor axons and contraction fatigability during functional electrical stimulation (FES). We found that axonal excitability decreased, and contraction fatigability increased, with increases in FES frequency. This is consistent with the idea that during FES, motor axons become less excitable and "drop-out" as they hyperpolarize and this contributes markedly to contraction fatigability. Strategies that minimize the hyperpolarisation of motor axons may help maximize the benefits of FES-based programs.