Objective: The aim of this study was to assess overall inspiratory muscle activity during incremental exercise in obese men and healthy controls using the non-invasive, inspiratory muscle tension-time index (T(T0.1)). We studied 17 obese subjects (mean age+/-s.d.; 49+/-13 years) and 14 control subjects (42+/-16) during an incremental, maximal exercise test.
Methods: Measurements included anthropometric parameters, spirometry, breathing patterns and inspiratory muscle activity. T(T0.1) was calculated using the equation T(T0.1)=P(0.1)/P(Imax) x T(I)/T(TOT) (where P(0.1) is mouth occlusion pressure, P(Imax) is maximal inspiratory pressure and T(I)/T(TOT) is the duty cycle).
Results: At same levels of maximal exercise (%W(max)) (20, 40, 60, 80, 100% W(max)), obese subjects showed higher P(0.1) (P<0.001) and P(0.1)/P(Imax) (P<0.001) values than controls. T(T0.1) was thus higher in obese subjects for each workload increment and at maximal exercise (P<0.001).
Conclusions: During exercise, patients with obesity show alterations in inspiratory muscle activity as a result of both reduced inspiratory strength (as measured by maximal inspiratory pressure) and increased ventilatory drive (as reflected by mouth occlusion pressure), which prone obese subject to respiratory muscle weakness. Our results suggest that impaired respiratory muscle activity could contribute to a decrease in exercise capacity. T(T0.1) may be useful in our understanding concerning the benefits of endurance training.