Effect of weight loss on operational lung volumes and oxygen cost of breathing in obese women

BACKGROUND: The effects of moderate weight loss on operational lung volumes during exercise and the oxygen (O-2) cost of breathing are unknown in obese women but could have important implications regarding exercise endurance. METHODS: In 29 obese women (33 +/- 8 years, 97 +/- 14 kg, body mass index: 36 +/- 4 kg m(-2), body fat: 45.6 +/- 4.5%; means +/- s.d.), body composition, fat distribution (by magnetic resonance imaging), pulmonary function, operational lung volumes during exercise and the O-2 cost of breathing during eucapnic voluntary hyperpnea ((V)over dot O-2) vs ((V) over dot(E)) slope) were studied before and after a 12-week diet and resistance exercise weight loss program. RESULTS: Participants lost 7.5 +/- 3.1 kg or approximate to 8% of body weight (P<0.001), but fat distribution remained unchanged. After weight loss, lung volume subdivisions at rest were increased (P<0.05) and were moderately associated (P<0.05) with changes in weight. End-expiratory lung volume (percentage of total lung capacity) increased at rest and during constant load exercise (P<0.05). O-2 cost of breathing was reduced by 16% (2.52 +/- 1.02-2.11 +/- 0.72 ml l(-1); P = 0.003). As a result, O-2 uptake of the respiratory muscles ((V)over dotO(2Resp)), estimated as the product of O-2 cost of breathing and exercise ((V) over dot(E)) during cycling at 60 W, was significantly reduced by 27 +/- 31 ml (P<0.001), accounting for 46% of the reduction in total body ((V)over dot O-2) during cycling at 60 W. CONCLUSIONS: Moderate weight loss yields important improvements in respiratory function at rest and during submaximal exercise in otherwise healthy obese women. These changes in breathing load could have positive effects on the exercise endurance and adherence to physical activity.