The effects of pain and fatigue on regulation of exercise performance

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Fatigue and pain perceived during intensive exercise has long been associated with a transient reduction in exercise tolerance. These perceptual responses have been attributed to an interplay of several physiological and psychological factors among which activation of mechano- and metabo-sensitive group III/IV muscle afferents are well recognized. In addition to conscious sensation of fatigue and pain, activation of group III/IV sensory afferents has been shown to be critical for regulation of neuromuscular (NM) and cardiovascular (CV) responses. However, little is known about how NM, CV, and perceptual responses integrate to determine exercise tolerance. To study the impact of group III/IV sensory feedback responses on exercise tolerance, previous literature has mainly focused on the application of pharmacological agents (e.g., aspirin and caffeine); however, less attention has been paid to potential analgesic effects of exercise on fatigue and pain modulation. Indeed, exposure to exercises approaching the maximal pain tolerance, such as high intensity interval training (HIIT), has been shown to mitigate perceptual responses to exercise. Thus, the long-term objective of my research program is to explore how acute and chronic physiological and perceptual mechanisms integrate to determine exercise tolerance. In striving to meet this objective, my short-term objectives are to: 1.Explore pain tolerance and its relationship with NM, CV and perceptual responses to a fatiguing exercise in individuals with different training backgrounds; 2.Study the effect of different exercise interventions, specifically high intensity interval training (HIIT), on acute and chronic physiological and perceptual responses determining exercise tolerance; 3.Investigate the acute and chronic effects of exercise interventions on central nervous system (brain and spinal cord) responses using transcranial magnetic and electrical stimuli, and neuroimaging techniques such as functional near infrared spectroscopy (fNIRS). Experimental protocols in my research program will be carried out on an innovative custom-built recumbent cycle ergometer that facilitates the post-fatigue NM evaluation within a second. The NM measurements will include a series of maximal and submaximal isometric knee extensions superimposed with transcranial magnetic and electrical stimuli (to assess NM performance and corticospinal excitability/inhibition); CV assessments will include mean arterial pressure, heart rate, gas-exchange and ventilation; and perceptual responses will include rating of perceived exertion, arousal, general fatigue, and pain. Better understanding the integration between NM, CV and perceptual determinants of exercise tolerance throughout a series of cross-sectional and training studies proposed in my research program will generate new knowledge for the development of non-pharmacological methods to improve exercise performance.