We studied the effect of abdominal loading on exercise performance in 7 patients with severe chronic air-flow obstruction (CAO). The patients were exercised to exhaustion on a bicycle ergometer at a work rate equivalent to 80% of their maximal work rate. Three exercise studies were completed in the same afternoon. The first and third were control studies; in the second, the abdomen was strapped with a belt that was secured after the patient had expired below FRC. Neither TLC (p greater than 0.3) nor FRC (p greater than 0.05) were altered by strapping. Exercising with the abdomen strapped resulted in a 40% increase in transdiaphragmatic pressure (Pdi) (p less than 0.005), but neither the peak inspiratory pleural pressure relative to the relaxation curve nor the minute ventilation differed from those of the control study (p greater than 0.7). Nevertheless, strapped exercise endurance (119 +/- 27 s) was significantly lower than control endurance (154 +/- 35 s; p less than 0.01). Because of the increase in Pdi, the computed tension-time index of the diaphragm increased from a control value of 0.13 +/- 0.05 to 0.20 +/- 0.06 (p less than 0.05) when strapped. However, neither the pleural pressure nor the Pdi swings decreased during the last 30 s of the runs, indicating that inspiratory muscle fatigue was not the basis for the reduced endurance when the abdomen was strapped. Strapping the abdomen may improve the length-tension relationship of the diaphragm at a given lung volume, and the increased Pdi suggests improved diaphragmatic function.(ABSTRACT TRUNCATED AT 250 WORDS)