Physical Fitness Associated with Lower Mortality? Association of Cardiorespiratory Fitness With Long-term Mortality Among Adults Undergoing Exercise Treadmill Testing

A recent study published in the Journal of American Medical Association showed that higher level of cardiorespiratory fitness (CRF) was associated with decreased long-term mortality with no observed upper limit of the CRF level that could induce the benefit. Moreover, extremely high aerobic fitness was associated with the greatest survival and was associated with benefit in older patients and those with hypertension. 

This retrospective cohort study looked at the data of 122,000 patients who were referred for symptom-limited exercise treadmill testing at a tertiary care academic medical center between the years 1991 and 2014. The patients were stratified according to the fitness level into five groups: low, below average, above average, high, and elite. An inverse relationship was found between CRF and all-cause mortality during the follow-up period. The elite performers had the lowest mortality risk even when compared to the high group performers and after adjusting for possible confounders (HR 0.77; 95% CI 0.63-0.95; P = .02). Interestingly, the increased mortality associated with low fitness was comparable to the increased mortality risk from recognized cardiovascular risk factors such as smoking, diabetes, and coronary artery disease. The decreased risk of mortality noted in the elite performers when compared with the high performers was significant in patients with hypertension (HR 0.70; 95% CI 0.50-0.99; P= .05) and in patients aged 70 years or older (HR 0.71; 95% CI 0.52-0.98; P= .04).

 

Dr. Paul Cremer (Cleveland Clinic Foundation, Cleveland, Ohio) commented, “There are two important conclusions. First, there is no threshold to the benefit on increased exercise capacity, and patients with the highest functional capacity have the best long-term survival. Second, the risk associated with a poor exercise capacity is comparable, or even worse, than the risk of other comorbidities that we often consider, such as CAD, smoking, and diabetes mellitus.” Recent studies demonstrated an association between extreme physical activity with adverse cardiovascular outcomes such as increased risk of atrial fibrillation and coronary artery calcifications. However, the current study showed that higher CRF was associated with lower all-cause mortality which raised the question: Were these outcomes a sign of pathology or a result of adaptation?

It was also noted in the subgroup analysis that there was no significant benefit of increased CRF in patients with diabetes, coronary artery disease, and hyperlipidemia due to the limited number of individuals with these comorbidities in the elite group. Dr. Cremer added, “Previously, there has been controversy on whether patients with the highest level of exercise capacity have improved prognosis with the suggestion that these patients have a similar prognosis, or even, a worse prognosis compared to patients with preserved exercise capacity. In patients referred for stress testing, we do not find a plateau in benefit or increased harm in patients with the highest functional capacities.”

“These findings should definitely impact clinical practice. For one, we should encourage aerobic exercise in our patients, and for our sedentary patients, we should discuss the impact on their overall health as similar in magnitude to other established cardiovascular risk factors. Second, in patients being considered for stress testing, we cannot emphasize enough the importance of exercise testing as the most valuable prognostic information appears to be their functional capacity,” he concluded.