The aim of this study was to assess the effects on performance and work capacity of a short-term (3-week) integrated body weight reduction programme consisting of an energy-restricted diet, nutritional education, psychological counselling and aerobic exercise training at a constant metabolic load (5 days/week) in 71 severely obese patients (18 males and 53 females aged 29.3 +/- 0.8 years, with a mean weight of 113.8 +/- 2.2 kg and a mean BMI of 41.3 +/- 0.5 kg/m(-2)). Body mass and composition, and maximum oxygen consumption (VO2max) were determined before and after the programme. The caloric equivalent of work output and a performance index (PI) during 10 min of bicycle ergometer pedalling (50-60 rpm) and 20 min of treadmill walking (incline 0-3%) at a constant metabolic load (50% of individual VO2max during the preliminary conditioning period--1st week--and 60% during the exercise conditioning period--2nd and 3rd week) were evaluated daily throughout the study. After the programme, body mass reduced significantly (-4.5%, p<0.001), the weight loss being sustained entirely by a significant reduction in fat mass (-7.6%, p<0.001) without any significant changes in fat-free mass. Absolute and body mass-related VO2max significantly increased by respectively 14.5% and 20.2% (p<0.001). Both daily work output during constant metabolic load (ANOVA, p<0.05-0.001) and PI (ANOVA, p<0.05-0.001) increased significantly during each week of the programme, leading to a total increase in work output in response to exercise conditioning of 44.6 +/- 5.8 kcal. It is concluded that the changes in exercise capacity induced by the present programme offer significant advantages for obese patients that can be quantified in terms of an improvement in their ability to perform everyday activities, thus contributing towards improving their quality of life.