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OBJECTIVE The purpose of this study was to compare the effects on exertional dyspnea and exercise capacity of square wave (bilevel) cycle ergometry endurance exercise training (SWEET) and comprehensive directed breathing vs. walking while pushing an OxCar and traditional diaphragmatic breathing for male smokers with normal spirometry but reduced exercise capacity. DESIGN This was a prospective randomized trial of 24 unmedicated men with exertional dyspnea assigned to SWEET or OxCar groups. Exertional dyspnea was assessed using the Borg scale during four tests: incremental exercise, constant exercise at 80% of the peak work rate (PWR) (maximum tolerated for 3 mins before exhaustion), SWEET, and 6-min walk test. Both groups trained for 45 mins, 5 days a week, for 6 wks. Before, during, and after training, 32 lung function parameters were studied at ventilatory anaerobic threshold, at PWR, and during incremental exercise (30 W/3 mins). RESULTS For the SWEET group, exertional dyspnea and the dyspnea index decreased during incremental exercise, at the ventilatory anaerobic threshold, and at PWR (P < 0.01). At the ventilatory anaerobic threshold, oxygen consumption increased by 74%; minute ventilation, 30%; tidal volume, 91%; and ventilatory efficiency and oxygen pulse (O(2)P), 25%; and breathing rate (breathing frequency) decreased by 32% (all significant at P < 0.001). At PWR, oxygen consumption increased by 30%; minute ventilation, 37%; breathing rate, 21%; and ventilatory efficiency and oxygen pulse, 25% (P < 0.01). During the full incremental test, minute ventilation, breathing frequency, and heart rate (cardiac frequency) decreased significantly (P < 0.01). In addition, there was significant improvement (P < 0.001) in SWEET intensity by 63%, constant exercise intensity at 80% of PWR by 38%, and 6-min walk test by 30%. No significant changes were observed for the OxCar group other than for the 6-min walk test, which increased by 7% (P < 0.05). CONCLUSIONS This study suggests that the decline in exercise tolerance for male smokers can be reduced by intensive exercise training (SWEET) and comprehensive directed breathing but not by moderate training and traditional diaphragmatic breathing. Thus, some smokers can be helped despite continuing to smoke.