Table 1.

Main parameters assessed by peripheral nerve stimulation and transcranial magnetic stimulation to evaluate muscle fatigue or exercise-induced alterations in peripheral and corticospinal excitability and inhibition.

Technique		Variable	Parameter assessed	Interpretation as related to exercise
Peripheral nerve stimulation		Mmax	Sarcolemmal excitability	↓ amplitude: ↓ sarcolemmal excitability
		Resting twitch	Peripheral muscle contractility	↓ amplitude: peripheral fatigue
		Peripheral VA	Maximal voluntary activation	↓ level: central fatigue
Transcranial magnetic stimulation	Single-pulse	MEP	Corticospinal excitability	↓ amplitude: ↓ corticospinal excitability
		CSP	Duration of intracortical GABAB-mediated inhibition	↑ duration: ↑ intracortical inhibition
		SIT	Supraspinal deficit	↑ amplitude: ↑ supraspinal deficit
		Supraspinal VA	Supraspinal voluntary activation	↓ level: supraspinal fatigue
	Paired-pulse	SICI	Magnitude of intracortical GABAA-mediated inhibition	↓ conditioning-to-test stimuli ratio: ↑ intracortical inhibition
		LICI	Magnitude of intracortical GABAB-mediated inhibition	↓ conditioning-to-test stimuli ratio: ↑ intracortical inhibition

CSP, cortical silent period; GABA, gamma-aminobutyric acid; LICI, long-interval intracortical inhibition; MEP, motor-evoked potential; Mmax, maximal muscle compound action potential; SICI, short-interval intracortical inhibition; SIT, superimposed twitch; VA, voluntary activation. Exercise-induced reduction (from baseline) in the resting twitch, voluntary activation assessed by peripheral nerve stimulation and voluntary activation assessed by transcranial magnetic stimulation respectively indicate peripheral, central and supraspinal fatigue (for further elaboration, see Investigating the brain on exertion: theoretical framework and key definitions).