Small Gains in Cardiorespiratory Fitness Track With Improved Longevity

As previously suspected, changes in cardiorespiratory fitness (CRF) were associated with reciprocal changes in mortality risk independent of other comorbidities or initial fitness status, a large observational study found.

People who had serial exercise treadmill test assessments, with a median 6 years between initial and final tests, showed that changes in aerobic capacity over time tracked with better or worse survival outcomes, reported a group led by Peter Kokkinos, PhD, an exercise physiology specialist at Veterans Affairs Medical Center in Washington, D.C.

Whereas changes in CRF of ≥1.0 peak metabolic equivalents (METs) were associated with mortality over a median 6.3 years of follow-up, the difference in survival was more prominent with larger rises and falls in CRF, regardless of baseline cardiovascular disease (CVD). For example, a CRF drop of at least 2.0 METS was tied to a 69-74% increased mortality risk among low-fit individuals:

• Without CVD (HR 1.69, 95% CI 1.45-1.96)
• With CVD (HR 1.74, 95% CI 1.59-1.91)

“These findings provide a guide for clinicians and the public in general regarding CRF changes necessary to improve CRF and health outcomes. Accordingly, encouraging the public to improve CRF by at least 1.0 MET can have considerable clinical and public health significance,” study authors reported in the March 23 issue of the Journal of the American College of Cardiology.

The present report confirms and extends the prior literature linking cardiorespiratory capacity and mortality, according to Leonard Kaminsky, PhD, a clinical exercise physiologist at Ball State University in Muncie, Indiana, and colleagues, writing in an accompanying editorial.

“In fact, the prognostic utility of CRF outperforms commonly assessed clinical CVD risk factors, such as lipids, blood pressure, body habitus, smoking, and blood glucose,” said Kaminsky and co-authors, who suggested that CRF testing be used more widely than its usual limited applications in diagnostics or for assessing organ transplant candidacy.

“Although exercise testing before initiating an exercise intervention is not required, assessing one’s hemodynamic and cardiorespiratory responses to graded exercise testing can facilitate the customization of an exercise prescription to optimize improvements in CRF and other health-related factors,” the editorialists wrote.

“We (again) call on both clinicians and public health professionals to adopt CRF as a key health indicator. This should be done by coupling routine assessments of CRF with continued advocacy for promoting physical activity as an essential healthy lifestyle behavior,” they urged.

One MET is defined as the amount of energy a person uses while sitting still. Vigorous activities such as running tend to spend at least 6.0 METs.

Most adults who begin a moderate-to-vigorous aerobic exercise program can significantly increase their CRF by 1 to 2 METs, according to the HERITAGE Family Study report cited by Kaminsky and colleagues.

In the present study, CRF increased by at least 1 MET in approximately 29% of individuals and decreased in approximately 46%. “This finding underscores the need to promote physical activity to maintain or increase CRF levels in middle-aged and older individuals,” Kokkinos and colleagues stressed.

The investigators had relied on data from the ETHOS cohort of over 750,000 individuals who had completed an exercise treadmill test evaluation at a VA Medical Center from 1999 to 2020 using the Bruce protocol.

The analysis included 93,060 adults who achieved ≥2.0 METS and had a minimum of two tests completed at least 1 year apart and had no evidence of overt CVD.

Men constituted the vast majority of participants, who averaged age 61.3. Nearly three-fourths were white and 20% were Black.

Mortality occurred at an average yearly rate of 27.6 events per 1,000 person-years.

A sensitivity analysis accounting for reverse causality did not materially change the study’s main results: exclusion of patients who likely had underlying disease (having a decline in CRF and dying within 2 years of the last exercise treadmill test) did not negate the association between changes in CRF and mortality risk.

Kokkinos’ team acknowledged that the retrospective, observational study cannot tell when “reductions in CRF were the outcome of intentional abstinence from physical activity, other lifestyle factors, or subclinical disease that underlies low CRF (reverse causality), despite steps taken to minimize the possible impact of reverse causality.”

Moreover, CRF was not based on direct assessment of VO₂ max but approximated by METs alone.