A prospective evaluation of cardiopulmonary tolerance to maximal exercise in adolescent idiopathic scoliosis. To evaluate ventilatory functional restrictions during a maximal exercise tolerance test in idiopathic scoliosis patients with mild and moderate curves and to compare them with the results obtained in healthy adolescents matched in age undergoing similar test. Adolescents with idiopathic scoliosis with mild curves do not exhibit significant restrictions in ventilatory parameters measured by conventional static spirometry. Few reports have dealt with cardiorespiratory response to maximal exercise in adolescent idiopathic scoliosis with mild to moderate curves. Although results seem to show a reduced exercise tolerance in these patients, the frequency and signification of the restricted work capacity is uncertain because of important design limitations in previous studies. Thirty-seven girls diagnosed with adolescent idiopathic scoliosis with a mean age of 13 years (range, 11-16) and an average scoliotic curve of 32.8 degrees Cobb (range, 20-45 degrees) were studied by basal spirometry and dynamic ventilatory parameters during a maximal exercise tolerance test. Similar studies were performed in a control group of 10 healthy girls matched in age. Exercise test consisted of a ramp protocol on treadmill starting at a speed of 0.75 m/second (2.7 km/hour) with increments of 0.2 m/second (0.72 km/hour) per minute. All subjects completed the test to exhaustion to determine maximal oxygen uptake (VO2 max) and ventilatory efficiency parameters. There were no differences between scoliotic and healthy girls in basal ventilatory parameters (FVC, FEV1). However, adolescents with idiopathic scoliosis showed worse tolerance to exercise test with lower maximal speed average (9.4 km/hour versus 11.5 km/hour, P < 0.005), lower ventilatory efficiency at maximal exercise (VE: 68.9 L/minute versus 82.3 L/minute, P < 0.01), early anaerobic threshold, and a lower aerobic power expressed by 23% decreased body weight normalized VO2 max (38.6 mL/kg/minute versus 49.0 mL/kg/minute, P < 0.001). VEmax values were correlated to the severity of the scoliotic curve. Patients with more severe curves had greater limitation of ventilatory capacity (r = -0.374, P < 0.05). Maximal breath frequency was higher in scoliotic girls (54 versus 47, P < 0.05) suggesting a compensatory mechanism adopted in response to the lower ventilatory capacity during demanding exercise. When ventilatory efficiency was considered by the VE/VO2 ratio, scoliotic girls disclosed higher values than control (average 35.2 versus 29.6, P < 0.001) indicating an inefficiency in their ventilation. Patients wearing a brace at the time of ventilatory functional assessment did not exhibit any difference in the parameters investigated both at basal spirometry and during exercise tolerance test. Although patients with mild or moderate scoliosis do not exhibit cardiopulmonary restrictions in basal static conditions, they do show a significant lower tolerance to maximal exercise. Respiratory inefficiency together with lower ventilation capacity and lower VO2 max may be responsible for reduced exercise tolerance in adolescents with idiopathic scoliosis. Exercise deconditioning in scoliotic patients cannot be attributed to brace treatment.