The cholinergic system did not modulate MEPs or SPs under conditions of fatigue
failure of the muscle, fatigue
CONTRACTIONS
Fatigue-inducing contractions cause a reduction in the maximal force generating capacity of the muscle, where the decline in force may be due to an inability of the nervous system to activate the muscle, or a failure of the muscle itself to contract. The current study normalised the amount of fatigue that was induced for each participant and assessed corticospinal excitability by normalising the MEP to Mmax. These procedures allow us to identify the role that mAChR blockade has on fatigue-related central motor responses. Surprisingly, the administration of promethazine did not affect any measurement of corticospinal excitability (or TMS-evoked SP), which suggests that mAChRs have no role in muscle activation while experiencing significant amounts of fatigue. Our previous work examined antimuscarinic effects on MEP area immediately following a fatigue-inducing 60 s MVC. In doing, we revealed that MEP area was increased from resting levels by 153% for a promethazine condition and 131% for a placebo condition, with MEPs for both conditions returning to resting levels in less than 10 s (Dempsey and Kavanagh 