Figure 2.
Experimental protocol to derive corticospinal excitability stimulus-response curves and median split. A: corticospinal excitability was assessed in the dominant first dorsal interosseus and vastus lateralis in n = 53 individuals following a series of maximum voluntary contractions (MVCs). B: for each muscle, a total of 40 pulses were delivered during eight 25 s sets of isometric contractions at 15%MVCs, with five pulses applied at random 5% increments of stimulator output (range: 5%–100%) per set. C: representative motor-evoked potentials (MEPs) at select percentages of stimulator output were (D and E) fitted to a Boltzmann sigmoidal curve to derive muscle-specific stimulus-response-curves for each day. Corticospinal excitability was then determined as the plateau (MEPMAX) of the stimulus-response-curve. F: neither lower nor upper limb corticospinal excitability changed throughout the intervention, but a persistent bimodal distribution of lower limb MEPs was evident. As a result, we divided the sample into individuals with HIGH (n = 27) and LOW (n = 26) corticospinal excitability of the VL using a median split of baseline (Day 1) MEPMAX.