Neurophysiological Responses to Fatiguing Exercise above Critical Power in Healthy Humans

  • Lisa U. Schafer

Student thesis: Doctoral Thesis

Abstract

Substantial levels of peripheral fatigue, i.e. reduction in the force-generating capacity induced by alterations at or distal to the neuromuscular junction, have been evidenced within the severe intensity domain. The primary aim of this thesis was to better understand the mechanism(s) of these exercise-induced neurophysiological alterations following severe intensity cycling exercise applying the critical power (CP) concept. The CP concept mathematically defines the relationship between power output and the tolerable duration of severe intensity exercise using a hyperbolic relationship with CP and Wʹ, the power asymptote and the curvature constant, respectively.

Study 1 examined the between-day reliability of key neuromuscular measures in the knee extensor muscles at rest and following severe intensity cycling exercise using femoral nerve stimulation. The reliability of key neuromuscular measures in the fresh and fatigued state were acceptable, with slightly greater variation in most measures following severe intensity cycling exercise. To our knowledge, Study 2 was the first study to demonstrate that neuromuscular fatigue observed after full depletion of Wʹ is of similar magnitude whether supra-CP cycling exercise is performed close to the lower boundary for 12 min of exercise (P-12) or close to the upper boundary for 3 min of exercise (P-3) of the severe intensity domain. Further, exploratory analysis showed that smaller changes in the muscular force-generating capacity are seen in individuals with greater aerobic capacities (CP, V̇O2peak) for P-12, but greater changes in individuals with greater anaerobic capacities (Wʹ) for P-3. In Study 3, neuromuscular recovery following P-3 and P-12 was investigated. Both, central and peripheral alterations remained below baseline after 30 min of rest irrespective of exercise intensity and duration above CP. Based on the findings from Study 2, Study 4 aimed to increase Wʹ and examine its effect on neuromuscular fatigue following severe intensity cycling. Creatine supplementation increased severe intensity cycling performance and thus, Wʹ. However, despite the positive relationship between Wʹ and neuromuscular fatigue found for P-3 in Study 2, the greater Wʹ due to creatine supplementation did not lead to a greater level of neuromuscular fatigue at task failure in Study 4.

In conclusion, these findings suggest that similar levels of neuromuscular fatigue and a similar time course of neuromuscular recovery can be observed following severe intensity cycling exercise when Wʹ is fully depleted, irrespective of the exercise intensity selected within the severe intensity domain. Further, the magnitude of neuromuscular fatigue at task failure does not depend on the size of Wʹ.
Date of AwardJul 2019
Original languageEnglish
Awarding Institution
  • University of Brighton
SupervisorJeanne Dekerle (Supervisor) & Mark Hayes (Supervisor)

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