Temporal characteristics of diaphragmatic fatigue and inspiratory muscle training effects during high-intensity exercise in healthy adults

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) The diaphragm is the principle muscle of inspiration and is subject to fatigue during whole-body exercise at intensities above 85% of maximal oxygen consumption (V̇O2). Exercise-induced diaphragmatic fatigue (DF) generates higher perceptions of dyspnea and limb fatigue, it onsets the respiratory muscle metaboreflex and, consequently, limiting high-intensity exercise (HIE). Inspiratory muscle training (IMT) is highly efficient to provide gains in respiratory muscle strength (RMS), and to promote greater HIE and athletic performance. This thesis is composed by two studies. The objective of Study I was to investigate temporal characteristics of exercise-induced diaphragmatic fatigue (DF) during HIE in healthy adults. Ten healthy men were recruited in the initial screening and 8 were included in the final analysis. Initially, anthropometrics and spirometry were assessed, followed by a cardiopulmonary exercise test (CPET) in a cycle ergometer. Another 3 tests were performed using the Δ60% method to calculate the workload. The first was performed to time-to-exhaustion (TTE) while the other 2 were randomly applied to 50 and 75% of TTE. DF was assessed using the balloon catheterization method and through the calculation of transdiaphragmatic twitch pressure after cervical magnetic stimulus. DF was found from 75% TTE (P