Factors associated with electrical stimulation-induced performance fatigability are dependent upon stimulation location.

Neuromuscular electrical stimulation (NMES) is increasingly viewed as a central tenet to minimise muscle loss during periods of disuse/illness - typically applied directly over a muscle belly. Peripheral nerve stimulation (PNS) is afforded less attention, despite providing a more global contractile stimulus to muscles. We investigated NMES versus PNS in relation to performance fatigability and peripheral contributions to voluntary force capacity. Two fatigue protocols were assessed separately: (1) over-quadriceps NMES and (2) peripheral (femoral) nerve stimulation (PNS). Before and after each session, a maximal voluntary contraction (MVC) was performed to assess force loss. Knee-extensor force was measured throughout to assess contractile function in response to submaximal electrical stimulation, and M-wave features quantified myoelectrical activity. NMES and PNS induced similar voluntary (MVC, NMES: -12 ± 9%, PNS: -10 ± 8%, both P < 0.001) and stimulated (NMES: -45 ± 12%, PNS -27 ± 27%, both P < 0.001) force reductions. Although distinct between protocols, myoelectrical indicators of muscle recruitment (M-wave area and amplitude) and nerve conduction time did not change throughout either protocol. Myoelectrical propagation speed, represented as M-wave duration, and the delay before muscle relaxation began both progressively increased during NMES only (P < 0.05 and P < 0.001, respectively). NMES myoelectrical changes suggested performance fatigability, indicating activation of superficial fibres only, which was not observed with PNS. This suggests PNS recruits a wider pool of muscle fibres and motor units and is a favourable alternative for rehabilitation. Future work should focus on implementing PNS interventions in clinically relevant scenarios such as immobilisation, care homes and critical illness.