A recent British Journal of Sports Medicine study examines the predictive relationships between cardiorespiratory fitness (CRF) and health outcomes in adults.

Study: Cardiorespiratory fitness is a strong and consistent predictor of morbidity and mortality among adults: an overview of meta-analyses representing over 20.9 million observations from 199 unique cohort studies. Image Credit: UfaBizPhoto / Shutterstock.com

What is CRF?

CRF, which is key to the proper functioning of several bodily systems, aids in the usage of oxygen and supporting muscles during physical activity. Genetics contributes to about 50% of the variance in CRF across individuals, whereas habitual physical activity is another major factor in determining CRF. 

CRF is not regularly assessed in clinical practice; however, its inclusion could enhance the identification of high-risk individuals, thereby helping in patient management. Prior research has shown an association between CRF and type 2 diabetes, stroke, certain cancers, and depression. In individuals with chronic conditions, a higher CRF could improve the prognosis.

About the study

The current study involved a meta-analysis of published reviews on the relationship between CRF and health outcomes. The certainty of evidence was assessed for each health outcome, including incident conditions linked to physical risk factors, all-cause or cause-specific mortality, mental health issues, and chronic conditions.

Studies that concentrated on specific patient populations, such as those recovering from surgery, pregnant individuals, or athletes, were excluded from the study. CRF was primarily measured by maximal exercise testing with gas analysis expressed as V̇O_2max/peak  and maximal or submaximal exercise testing without gas analysis, which was assessed using the measured exercise performance or exercise prediction equations. CRF was also measured using non-exercise prediction equations. 

The analysis included 26 systematic reviews, 199 unique cohort studies, and a combined sample size of 20.9 million observations.

Study findings

CRF was a consistent and robust predictor of risk across several mortality outcomes. Higher CRF was associated with a better prognosis in patients with chronic conditions, such as heart failure and cancer. Comparatively, low CRF was a key risk factor for the development of stroke, hypertension, dementia, and depression.

A significant dose-response effect was observed for every single metabolic equivalent of task (MET) of CRF. Thus, 1-MET reflects a clinically important difference (MCID) for CRF that could be considered as a target for interventions. The consistency and validity of the evidence across a wide array of health outcomes lend credence to the importance of CRF for public health surveillance and clinical assessments.

Several benefits are associated with regularly measuring CRF compared to traditional measures such as blood pressure and cholesterol. For example, considering the close association with physical exercise, CRF could help in guiding exercise prescription.

Moderate physical activity can lead to notable improvements in CRF in individuals with low CRF based on sex, age, or health status. Moreover, CRF tests can be implemented with a variety of tests depending on time and space limitations.

Conclusions

High CRF is consistently and strongly associated with a lower risk of incident chronic conditions, premature mortality, and poor prognosis in individuals with existing chronic conditions. The evidence across a range of outcomes was highly consistent, thus supporting the inclusion of CRF measurements in regular clinical and public health practice.

CRF could be an important risk stratification tool in clinical practice, as its predictive strength is preserved, irrespective of race, age, and sex. However, there remains an urgent need to develop proper clinical and public health guidelines that focus on the interpretation of the results and MCID of CRF across race, age, sex, and clinical populations.

Key strengths of the current study include examining the certainty of the evidence in varied situations, utilizing pooled meta-analyses from cohort studies, and assessing the quality of the systematic review.

The main limitation is similar to other overviews, where data quality is restricted to the included papers. For many of the meta-analyses reviewed in the current study, heterogeneity was high and unexplained by subgroup analyses. Furthermore, the evidence was confined to examining the relationship between a single measure of CRF and potential future health outcomes.