Caracterização temporal da fadiga diafragmática e dos efeitos do treinamento muscular inspiratório durante o exercício de alta intensidade em adultos saudáveis

Abstract

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<0,05); also, a strong and significant correlation was found between fatigue and diaphragmatic force output (r=0,785, P<0,001). We concluded that DF occurs during HIE and its magnitude increases as the work of breathing do so. Therefore, the diaphragmatic capacity to generate force and pressure becomes progressively smaller during HIE. In Study II we sought to investigate the effects of IMT on HIE tolerance, respiratory and peripheral muscles oxygenation, and performance during a repeated sprints ability test (RSA) in female soccer athletes. Eighteen athletes were included in the final analysis. Participants were randomly assigned into two groups: IMT (IMT, n=10), and sham (SHAM, n=8). As initial evaluation: anthropometrics, spirometry at rest, maximal mouth inspiratory (MIP) and expiratory static pressures assessment, CPET in a treadmill, time-to-exhaustion (TTE) constant load exercise test, and RSA test. After 60 sessions of intervention (2x/day, 5 days/week, 6 weeks; IMT and SHAM training at 50 and 15% MIP, respectively), the same tests were applied. A greater HIE tolerance was found post-intervention on both groups (TTE, P<0,05), however, only IMT group presented better respiratory and peripheral muscles oxygenation during high-intensity exercise (P<0,05). Both groups showed improvements on RSA test (both P<0,05). Such results indicate the potential role of IMT at better oxygenation and blood supply to peripheral muscles during HIE, also presenting a positive impact on inspiratory muscles strength, exercise tolerance, and RSA performance in women’s soccer athletes.