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Synapses
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
Virtually all synapses, including the NMJ, exhibit some form of short-term plasticity. In general, short-term plasticity is manifested under two conditions: Paired-pulse stimulation, resulting in paired-pulse facilitation or paired-pulse depression, according to whether the response to the second pulse is larger or smaller than the response to the first pulse, respectively.Stimulation by a train of high-frequency stimuli, referred to as tetanic stimulation.
Neuromuscular performance after rapid weight loss in Olympic-style boxers
Published in European Journal of Sport Science, 2020
Damir Zubac, Boštjan Šimunič, Alex Buoite Stella, Shawnda A. Morrison
In the present study, force output and voluntary activation were each significantly reduced after a 70% MVC fatiguing contraction, notably more so after RWL (Figure 2). These findings illustrate an insufficiency of the central nervous system (CNS) to fully activate the KE-s after undergoing 3% RWL. Presumably, voluntary drive (i.e. central fatigue development) was influenced by substrate depletion and fluid loss. These data are in line with a seminal paper from Nybo (2003), who demonstrated that exercise-induced hypoglycaemia (induced via 3 h cycling exercise at constant power output) modulated force output and VA levels of the KEs in endurance-trained participants after completing 120 s isometric contractions. However, Nybo did not report contractile characteristics of the KEs in this work. The VA deficit observed in the present study ran in parallel to reductions in resting doublet amplitude (by ∼9%), and shorter muscle half-relaxation times (by ∼30%, Table II). A previous review on non-combat athlete populations had proposed that the crucial steps of the excitation-contraction coupling are compromised by reductions in skeletal muscle glycogen concentrations (Ørtenblad, Nielsen, Saltin, & Holmberg, 2011). Little data on humans is currently available in the existing literature, however, in vitro mice studies have demonstrated that excitation-contraction coupling efficiency is glycogen dependent in the flexor brevis muscle (Chin & Allen, 1997). Indeed, Chin and Allen (1997) observed a reduction in Ca2+ release (by ∼43%) and depression in force production by ∼24%, under conditions of reduced glycogen concentration (by ∼27%), following intermitted 50 Hz tetanic stimulation, indicating that peripheral fatigue development was accelerated via substrate depletion and an inability to completely restore skeletal muscle glycogen concentrations (Ørtenblad, Westerblad, & Nielsen, 2013), especially following sustained contractions. Their findings indicated peripheral fatigue development. Conversely, data presented here suggest that the peripheral fatigue development, estimated via LFF index (Table II) t of the KE muscles, was non-significant and these changes in the LFF 20/80 ratio were consistent with data previously reported by Martin et al. (2010), who reported no notable changes in LFF in ultramarathon runners following a 24-h treadmill run.