Effect of Aerobic Exercise Training on Ventilatory Efficiency and Respiratory Drive in Obese Subjects
Résumé
BACKGROUND: Obese patients show a decline in exercise capacity and diverse degrees of dyspnea in association with mechanical abnormalities, increased ventilatory requirements secondary to the increased metabolic load, and a greater work of breathing. Consequently, obese patients may be particularly predisposed to the development of respiratory muscle fatigue during exercise. The aim of this study was to assess inspiratory muscle performance during incremental exercise in 19 obese male subjects (body mass index 41 +/- 6 kg/m(2)) after aerobic exercise training using the noninvasive, inspiratory muscle tension-time index (T-T0.1). METHODS: Measurements performed included anthropometric parameters, lung function assessed by spirometry, rate of perceived breathlessness with the modified Borg dyspnea scale (0-10), breathing pattern, maximal exercise capacity, and inspiratory muscle performance with a breath-by-breath automated exercise metabolic system during an incremental exercise test. T-T0.1 was calculated using the equation, T-T0.1 = P-0.1/P-Imax = T-I/T-tot (where P-0.1 represents mouth occlusion pressure, P-Imax is maximal inspiratory pressure, and T-I/T-tot is the duty cycle). RESULTS: At rest, there was no statistically significant difference for spirometric parameters and cardiorespiratory parameters between pre-and post-training. At maximal exercise, the minute ventilation, the rate of exchange ratio, the rate of perceived breathlessness, and the respiratory muscle performance parameters were not significantly different pre- and posttraining; in contrast, tidal volume (P =.037, effect size = 1.51), breathing frequency (P = .049, effect size = 0.97), power output (P = .048, effect size = 0.79), peak oxygen uptake (P = .02, effect size = 0.92) were significantly higher after training. At comparable work load, training induces lower minute ventilation, mouth occlusion pressure, ratio of occlusion pressure to maximal inspiratory pressure, T-T0.1, and rate of perceived breathlessness. CONCLUSIONS: Aerobic exercise at ventilatory threshold can induce significant improvement in respiratory muscle strength, maximal exercise capacity, and inspiratory muscle performance and decreased dyspnea perception in obese subjects.