Cardiorespiratory fitness (CRF) is a strong and independent predictor of mortality risk, however, it is unclear whether the association between CRF and mortality is mediated by the adoption of physical activity (PA; acquired CRF) or by underlying intrinsic CRF. In response we examined the association of intrinsic and acquired CRF on risk of all-cause mortality in men and women using follow-up CRF data from the Aerobics Centre Longitudinal Study cohort.
PURPOSE: To determine whether all-cause mortality risk differs between individuals who achieve high CRF through the adoption of PA compared to those who have intrinsically high CRF.
METHODS: A prospective study with at least two clinical visits (mean follow-up time: 14.0 (8.6) years) between 1974 and 2002 to assess CRF mortality risk in individuals who became active vs those who remained inactive at follow-up. Participants were 2,337 inactive men and women at baseline. Acquired CRF was defined as CRF of individuals who became active and improved CRF at follow-up, intrinsic CRF was defined as CRF of individuals who remained inactive at follow-up. The range of follow-up CRF values for both groups was set to 8-12 METs to achieve high (~10 METs) follow-up CRF values.
RESULTS: Individuals who had intrinsically high CRF at follow-up had a 20% reduced mortality risk for every 1 MET increase in CRF after adjusting for age, sex, follow- up weight (p<0.05). Hazard ratios were not materially different after further adjusting for change in systolic blood pressure, smoking, alcohol intake, diabetes mellitus, total cholesterol, abnormal ECG, family history of CVD (HR: 0.82 (0.68, 0.98); p<0.05). Individuals who had acquired a high CRF at follow-up had a 32% reduced mortality risk for every 1 MET increase in CRF after adjusting for age, sex, follow-up weight (p<0.05). Hazard ratios were not materially different after further adjusting for common risk factors associated with premature mortality (HR: 0.72 (0.59, 0.87); p<0.05).
CONCLUSION: While both intrinsic and acquired CRF were associated with a reduction in all-cause mortality risk, individuals who became active and improved CRF had a lower risk of all-cause mortality than those with intrinsically high CRF. This is the first analysis to show that the way in which CRF is achieved influences its association with mortality.