Research has shown that mortality is particularly high among those with the lowest levels of cardiorespiratory fitness (CRF). The increased mortality in this group is primarily thought to be due to cardiovascular disease and cancer. While a sedentary lifestyle is partly responsible for this excess risk, there is also a clustering of cardiovascular risk factors found in individuals with low CRF. The current study looked at these risk factors to assess potential mechanisms that explain their effect. An analysis of 82,000 subjects showed that triglyceride and non-HDL cholesterol levels, systolic blood pressure, diabetes, and metabolic syndrome were all increased as CRF decreased. These risk factors are mostly metabolic in nature. While regular exercise can increase CRF and improve metabolic risk factors, it is insufficient to explain the strong correlation between these metabolic risk factors and CRF. Increased body weight is also associated with low CRF. This is significant because obesity, particularly upper body obesity, has a negative impact on metabolic risk factors. It is also possible that insulin resistance may impair muscular function or cardiorespiratory capacity. Future research will be needed to determine the exact mechanism by which cardiovascular risk factors increase mortality among individuals with low CRF.
Grundy, S.M., et al. Cardiorespiratory fitness and metabolic risk. American Journal of Cardiology. 2012;109:988-993.