The purpose of this study was to assess whether obesity induces changes in breathing pattern and ventilatory neural drive and mechanics. Measurements performed in 34 male obese subjects (BMI, 39+/-6 kg/m(2)) and 18 controls (BMI, 23+/-3 kg/m(2)) included anthropometric parameters, spirometry, breathing patterns, mouth occlusion pressure, maximal inspiratory pressure and work of breathing. The results show that spirometric flow (FEV(1)% pred, FVC% pred) and maximal inspiratory pressure (P(Imax)) were significantly lowers (p<0.001) in obese subjects compared to controls. The (fR/VT) ratio was higher in obese subjects than in controls (p<0.001). The increase in (fR/VT) was associated with an increase in the ratio of mean inspiratory pressure to maximal inspiratory pressure (P(I)/P(Imax)) and the duty cycle (T(I)/T(TOT)) (p<0.001). The energy cost of breathing (W(rest)/W(crit)), which reflects the oxygen consumed by the respiratory muscle was greater in obese subject than in controls (p<0.001) inducing an increase in the effective inspiratory impedance on the respiratory muscles. It is concluded that obese subjects show impairment in breathing pattern and respiratory mechanics as assessed by rapid shallow breathing leading to ventilatory failure.