Age-Specific Exercise Capacity Threshold for Mortality Risk Assessment in Male Veterans

Abstract

Background— Mortality risk decreases beyond a certain fitness level. However, precise definition of this threshold is elusive and varies with age. Thus, fitness-related mortality risk assessment is difficult. Methods and Results— We studied 18 102 male veterans (8305 blacks and 8746 whites). All completed an exercise test between 1986 and 2011 with no evidence of ischemia. We defined the peak metabolic equivalents (METs) level associated with no increase in all-cause mortality risk (hazard ratio, 1.0) for the age categories of <50, 50 to 59, 60 to 69, and ≥70 years. We used this as the threshold group to form additional age-specific fitness categories based on METs achieved below and above it: least-fit (>2 METs below threshold; n=1692), low-fit (2 METs below threshold; n=4884), moderate-fit (2 METs above threshold; n=4646), fit (2.1–4 METs above threshold; n=1874), and high-fit (>4 METs above threshold; n=1301) categories. Multivariable Cox models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for mortality across fitness categories. During follow-up (median=10.8 years), 5102 individuals died. Mortality risk for the cohort and each age category increased for the least-fit and low-fit categories (HR, 1.51; 95% CI, 1.37–1.66; and HR, 1.21; 95% CI, 1.12–1.30, respectively) and decreased for the moderate-fit; fit and high-fit categories (HR, 0.71; 95% CI, 0.65–0.78; HR, 0.63; 95% CI, 0.56–0.78; and HR, 0.49; 95% CI, 0.41–0.58, respectively). The trends were similar for 5- and 10-year mortality risk. Conclusion— We defined age-specific exercise capacity thresholds to guide assessment of mortality risk in individuals undergoing a clinical exercise test.