BACKGROUND Endurance training improves cardiopulmonary fitness in maintenance haemodialysis (MHD). Because many MHD patients are profoundly deconditioned and exhibit significant muscle weakness, endurance training may also improve muscle strength and physical performance in these patients. This study assessed this possibility. METHODS Twelve MHD patients performed incremental and constant work rate cycle exercise tests to determine peak work rate, VO(2)peak and endurance time (ET). Lower extremity strength, power and fatigability, stair-climbing time, 10 m walk time and a timed up-and-go were assessed before and after 8.6+/-2.3 weeks of thrice weekly, progressive, semi-recumbent, leg-cycle training during haemodialysis. Initial training intensity and duration targets were set at 50% peak work rate (WR) and 20 min, respectively, with a goal of progressing to 40 min at the highest WR tolerable. Non-exercising MHD patients and healthy volunteers with similar age, gender and race/ethnicity served as comparison groups. RESULTS None of the subjects tolerated the initial target intensity. Therefore, WR was reduced to 19+/-9 watts (30% of peak WR) for 19.9 min/session. At end of training, subjects cycled at 29+/-25 watts (46% initial peak WR; P = 0.01) for 38+/-8 min (P<0.001). VO(2)peak and ET improved 22% (P = 0.018) and 144% (P = 0.001), respectively. Quadriceps strength, power and fatigability improved 16% (P = 0.002), 15% (P = 0.115) and 43% (P = 0.029), respectively. The three measures of physical performance improved by 14-17% (P<0.031). Total work performed in training increased by 5.5+/-21.1 kJ/week (17%); a 165% increase during the study period. CONCLUSIONS Nine weeks of leg-cycling during haemodialysis in MHD patients improves not only cardiopulmonary fitness and endurance but also muscle strength, power, fatigability and physical function. These data underscore the value of endurance training in MHD.