Cardiorespiratory Fitness Versus Physical Activity as Predictors of All-Cause Mortality in Men

Abstract

BACKGROUND: Physical activity (PA) is a behaviour, defined as any bodily movement that increases energy expenditure above resting levels, while cardiorespiratory fitness (CRF) is a physiologic trait that reflects the ability of the respiratory, circulatory, and musculoskeletal systems to deliver and utilize oxygen. Although both CRF and PA are inversely associated with mortality risk, whether they are associated independent of each other is unclear. METHODS: CRF was assessed by a maximal exercise test and PA was measured by self-report in 8171 male veterans. The predictive power of CRF and PA, along with clinical variables, was assessed for all-cause mortality during a mean (±SD) follow-up period of 8.7 (4.4) years during which there were 1349 deaths. RESULTS: CRF was associated with mortality after adjusting for traditional risk factors commonly measured in clinical practice, and remained a strong predictor of mortality after further adjusting for PA (hazard ratio [HR], 0.85; 95% confidence interval [CI], 0.83 –0.87). PA was a significant predictor of mortality after controlling for clinical variables, however the association was eliminated after further adjusting for CRF (HR, 0.98; 95% CI, 0.88 – 1.10). In CRF stratified analysis, being active (≥150 min/week) was not associated with mortality within the unfit or fit categories (p>0.4). However, in PA stratified analysis, subjects categorized as fit (≥7 METS) had a lower risk of mortality regardless of PA status (p<0.001). CONCLUSION: In adult men, PA was associated with mortality above and beyond established risk factors, but not CRF. Conversely, CRF remained a strong predictor of mortality, independent of PA status and established risk factors.