BackgroundLow cardiorespiratory fitness is strongly associated with cardiovascular diseases and mortality. Although increased physical activity can improve cardiorespiratory fitness, this relationship has not been examined in a large bariatric population undergoing perioperative care focusing on long-term lifestyle change.ObjectivesTo evaluate changes in physical activity, weight loss, and cardiorespiratory fitness up to 24 months after bariatric surgery, and to evaluate the relationships of change in physical activity with weight loss and change in cardiorespiratory fitness.Materials and MethodsFour thousand seven hundred eighty-five patients who underwent primary Roux-en-Y gastric bypass or sleeve gastrectomy between January 2012 and December 2014 were included. Physical activity was assessed by the Baecke questionnaire (work, leisure, and sport activity) and cardiorespiratory fitness, defined as VO2max relative to fat-free mass (VO2max/FFM), was assessed by the Åstrand test.ResultsTwenty-four months postoperative, significant improvements were seen in sport and leisure activity assessments (n = 3548, P < 0.001), weight loss (n = 3695, P < 0.001), and VO2max/FFM (n = 1852, P < 0.001). Furthermore, regression analysis showed that change in leisure activity was positively associated with weight loss (n = 3535, ß = 1.352, P < 0.001) and change in sport activity was positively associated with change in VO2max/FFM (n = 1743, ß = 1.730, P < 0.001).ConclusionBariatric surgery complemented by a comprehensive bariatric care program can lead to improvement in physical activity, as well as weight loss and improvement in cardiorespiratory fitness. The positive associations of change in leisure activity with weight loss and change in sport activity with cardiorespiratory fitness suggest that bariatric care programs can enhance postoperative outcomes by improving the patient’s physical activity.