Cardiorespiratory fitness and muscle strength in late adolescence and long-term risk of early heart failure in Swedish men

Aims: To investigate the association between cardiorespiratory fitness (CRF) and muscle strength in late adolescence and the long-term risk of heart failure (HF). Methods: A cohort was created of Swedish men enrolled in compulsory military service between 1968 and 2005 with measurements for CRF and muscle strength (n = 1,226,623; mean age 18.3 years). They were followed until 31 December 2014 for HF hospitalization as recorded in the Swedish national inpatient registry. Results: During the follow-up period (median (interquartile range) 28.4 (22.0-37.0) years), 7656 cases of first HF hospitalization were observed (mean +/- SD age at diagnosis 50.1 +/- 7.9 years). CRF and muscle strength were estimated by maximum capacity cycle ergometer testing and strength exercises (knee extension, elbow flexion and hand grip). Inverse dose-response relationships were found between CRF and muscle strength with HF as a primary or contributory diagnosis with an adjusted hazards ratio (95% confidence interval) of 1.60 (1.44-1.77) for low CRF and 1.45 (1.32-1.58) for low muscle strength categories. The associations of incident HF with CRF and muscle strength persisted, regardless of adjustments for the other potential confounders. The highest risk was observed for HF associated with coronary heart disease, diabetes or hypertension. Conclusions: In this longitudinal study of young men, we found inverse and mutually independent associations between CRF and muscle strength with risk of hospitalization for HF. If causal, these results may emphasize the importance of the promotion of CRF and muscle strength in younger populations.