Neuromuscular Electrical Stimulation Protocol

Two constant-current electric stimulators (STMISOLA, Biopac, USA) controlled by an USB-6343 interface (NI, USA) and custom-written program in Labview (NI, USA) were used to deliver the stimuli via low impedance carbon adhesive surface electrodes (area = 2cm² for each electrode). One stimulator was used to stimulate the fibular nerve at the fibular head and the other was used to stimulate the tibial nerve at the popliteal fossa [13 (link), 35 (link)]. Stimulation locations were determined both at rest and during contractions to take into account changes in muscle geometry during muscle contraction. Electrical stimulation parameters were determined during the familiarization session and confirmed during each experimental session before performing the fatiguing contraction.