Tolérance à l’effort global et fatigabilité musculaire dans les maladies respiratoires chroniques : Méthodes d’évaluation et identification des mécanismes neuromusculaires sous-jacents

This post-doctoral dissertation (habilitation) aims to provide a detailed synthesis of my research activities performed after my PhD, across the 2011-2019 period. I have gathered and presented some works with the intention to better describe and understand the limitations to physical exercise in chronic respiratory disorders (CRD). My approach suggests a complementary between whole-body exercise tests and isolated muscle assessments. The usefulness of these tests is exemplified through the presentation of several studies conducted in people with cystic fibrosis, chronic obstructive pulmonary disease (COPD) and obstructive sleep apnea.Collectively, some of our results suggest that each maximal and submaximal whole-body exercise test has its own interests and limitations. These tests should be viewed as complementary rather than interchangeable. The choice and frequency for the use of these tests should be considered with an individualized approach, taking into consideration the nature of the disease, its severity, some events modulating disease progression and hospital resources. Whole-body exercise tests, albeit useful to det ct and quantify exercise intolerance, are often less adapted to identify some of the underlying physiological mechanisms. In particular, the various neuromuscular abnormalities observed in people with CRD legitimize the evaluation of physical abilities using tests that isolate peripheral muscle function.Despite arguments supporting peripheral muscle abnormalities in cystic fibrosis, our studies suggest a preserved muscle metabolic function and contractility during local fatiguing exercises in individuals with mild to moderate lung disease. Some of our recent works now investigate the potential influence of CFTR genotype severity on peripheral muscle function in people with cystic fibrosis. Beyond peripheral factors, there are strong evidences supporting corticospinal abnormalities in CRD, especially in severe phenotypes, possibly linked with peripheral muscle dysfunction in these individuals. We found that cerebrovascular and corticospinal abnormalities observed at rest in people with severe obstructive sleep apnea persisted during physical exercise, with a potential contribution to reduced muscle strength, increased muscle fatigability or reduced maximal aerobic capacities.The last part of this dissertation is dedicated to the presentation of future research perspectives. I propose a rationale that legitimate the examination of limitations to physical exercise in aging individuals with CRD in demanding cognitive-motor contexts. We are currently investigating the hypothesis of a particular increase in muscle fatigability in people with COPD during cognitive-motor dual-tasks, related with abnormalities in central command. The traditional neuromuscular indicators are, however, somewhat limited for the understanding of such a complex phenomenon, which is influenced by several interconnected components (i.e. cortical, spinal, muscular). We are currently developing a methodology for facilitating the use of various indicators of neuromuscular complexity derived from nonlinear dynamics, in the specific context of muscle fatigability. The use of such indicators adapted to the study of the complexity of the neuromuscular system will allow shedding light on the psychophysiological limitations experienced by the individuals with CRD in demanding cognitive-motor contexts. Such investigations will favor the development of new treatment modalities in these specific populations

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