Mediating effects of exercise capacity on the association between physical activity and health‐related quality of life among adolescents with complex congenital heart disease

OBJECTIVES: There is little evidence on interrelationships between physical activity, sedentary behaviors, and health-related quality of life (HRQOL) among adolescents with congenital heart disease (CHD). We hypothesized that exercise capacity would have a mediating effect on the associations of either physical activity or sedentary behavior with HRQOL. METHODS: Adolescents with complex CHD (n = 111) were consecutively recruited from an outpatient clinic in a general hospital in South Korea. Physical activity and sedentary behavior were assessed using the global physical activity questionnaire. Exercise capacity was directly measured by peak oxygen uptake using a symptom-limited maximal treadmill exercise test. HRQOL was evaluated by both adolescents and their parents using the Pediatric Quality of Life Inventory questionnaire. RESULTS: The self-reported and parent proxy-reported HRQOL were positively associated with physical activity (ß = 0.16, P = .003; ß = 0.12, P = .049) and exercise capacity (ß = 0.63, P < .001; ß = 0.66, P < .001), but not with sedentary behavior in adjusted regression models. When both variables were entered in the same regression models, only exercise capacity remained significantly associated with the self-reported (ß = 0.50, P = .008) and parent proxy-reported HRQOL (ß = 0.62, P = .003). Exercise capacity acted as a full mediator variable on the relationship between physical activity and HRQOL (P < .05 for both). CONCLUSIONS: The present findings suggest that exercise capacity mediates the association between physical activity and HRQOL, highlighting the importance of improving exercise capacity to potentially enhance HRQOL in adolescents with complex CHD.