On the role of group III/IV muscle afferent feedback on endurance performance, neuromuscular fatigue, and autonomic adjustments to exercise

Afferent feedback mechanisms and reflex arcs represent fundamental regulatory systems for several processes such as motor control, proprioception, and autonomic adjustments to physiological stressors. Nowadays, compelling evidence exists that feedback mediated by group III/IV thin afferent fibers plays a quintessential role in contributing to maintain an appropriate locomotor muscle O2 delivery by facilitating cardiovascular and ventilatory responses to exercise and eventually delaying the onset of fatigue. Concurrently however, this feedback also inhibits neural drive to the muscle and facilitate central fatigue, which results in a negative effect on performance. Because of the ambivalent and “contradictory” nature of this feedback, the net effect on exercise performance and neuromuscular fatigue is still somewhat unclear. Throughout the years, many advancements have been done in this field through the discovery and optimization of the methods and tools apt to separate the influence of the different regulatory systems that contribute to the neurocirculatory adjustments to exercise. However, the redundancy existing in the regulation of physiological systems, make this endeavor challenging. In this dissertation, particular effort was put into separating the effects of group III/IV afferent feedback, from the potential effects played by the voluntary descending drive. Therefore, the purpose of this dissertation was to elucidate the role of group III/IV afferent feedback on exercise performance, neuromuscular fatigue, and autonomic adjustments to exercise in young healthy individuals. In Chapter 1, a brief introduction about the history of group III/IV afferent feedback is provided. In Chapter 2, a detailed literature review was performed in order to give a comprehensive background on the role of group III/IV afferent feedback on the autonomic adjustments to exercise, the neuromuscular fatigue processes, and exercise performance. In Chapter 3 the aims of the study are highlighted. Successively, Chapters 4, 5, and 6 include the results of the original investigations on this topic. Finally, Chapter 7 provides a summary and an ensemble view of our findings, highlighting strengths and weaknesses of our research, and providing future directions for further studies.