Examining the Gradient of All-Cause Mortality Risk in Women across the Cardiorespiratory Fitness Continuum.

Purpose: Although cardiorespiratory fitness (CRF) is inversely associated with all-cause mortality in women, less is known regarding the gradient of mortality risk in women, particularly at the lower end of the CRF continuum.

Methods: A total of 17,901 healthy women (mean age, 45.9 yr) completed a baseline clinical examination, including a maximal treadmill exercise test at the Cooper Clinic in Dallas, TX, between 1971 and 2016. Participants were placed into CRF quintiles based on age and treadmill time.

Results: After a mean follow-up period of 17.9 yr, 1198 all-cause deaths occurred. More favorable cardiometabolic risk factors, smoking status, and physical activity levels were observed across ordered CRF quintiles ( P < 0.001 for all). Adjusted all-cause mortality hazard ratios with 95% confidence intervals were 1.71 (1.40-2.09), 1.55 (1.29-1.87), 1.25 (1.03-1.51), 1.16 (0.97-1.38), and 1.0 (referent), respectively, across CRF quintiles ( P trend ≤ 0.001). When utilizing CRF as a continuous variable in a spline analysis and using 4.5 METs as the referent, we estimate a 10% reduction in mortality risk per 1-MET increment in CRF ( P < 0.001) until a threshold of approximately 11 METs. Mortality risk was approximately 50% lower at the 11-MET threshold when compared with the referent. No further significant reduction in mortality risk was observed beyond the 11-MET threshold. In addition, age-adjusted hemodynamic variables including resting and maximal double product, heart rate reserve, double-product reserve, and 1-min recovery heart rate were more favorable across CRF quintiles ( P < 0.001 for all).

Conclusions: Beginning at a referent value of 4.5 METs, a significant decreasing gradient of all-cause mortality exists across the CRF continuum, until a threshold of approximately 11 METs is reached. Although all women should be encouraged to work toward meeting public health guidelines for physical activity, it is especially important to target those at the low end of the CRF continuum.