Maximal exercise testing, including the determination of maximal performance and maximal oxygen uptake (VO(2max)), is considered the gold standard for assessing maximal endurance performance. The effectiveness of such testing is often reduced in haemophilic adults owing to musculoskeletal impairments or pain rather than because of cardiac exertion. The measurement of submaximal performance parameters overcomes many limitations of maximal exercise testing but a testing standard is still lacking. The aim of this study was to investigate maximal and particularly submaximal endurance performance of adult patients with severe haemophilia A and B. Eleven patients and 11 matched healthy controls were tested by spiroergometry with a specific treadmill test and the power was calculated in Watts. The haemophilic group achieved lower absolute (210 +/- 63 W) and weight-related (2.94 +/- 0.98 W kg(-1)) maximal endurance performance compared with the control group (287 +/- 50 W resp. 3.82 +/- 0.53 W kg(-1); P </= 0.05). The patients also showed a lower submaximal endurance performance at the individual anaerobic threshold (IAT = 147 +/- 56 W) and fixed lactate values (2 mmol = 98 +/- 60 W; 4 mmol = 158 +/- 56 W) compared with the healthy controls (IAT = 210 +/- 41 W; 2 mmol = 153 +/- 30 W; 4 mmol = 223 +/- 39 W; all P </= 0.05). The heart rate and lactate value at the IAT were not different. The disease-related musculoskeletal changes in haemophilic adults lead to a reduced maximal and submaximal endurance performance, which can be easily measured by the described test procedure.