The research, published in PLOS Aging and Health by Joey M. Saavedra of Iowa State University and colleagues, drew on data from the ongoing Physical Activity and Aging Study, a cohort of older adults living in the US Midwest. The team set out to answer a deceptively simple question: among people whose lungs are considered clinically healthy, does poorer pulmonary function still predict metabolic syndrome? And if so, is that relationship independent of relative grip strength—handgrip force divided by body weight—which is one of the most robust correlates of metabolic health known to exercise science?

To find out, the researchers enrolled 353 participants aged 65 to 95, of whom 63 percent were women. Each volunteer underwent spirometry, the gold-standard breathing test that measures how much air a person can forcibly exhale in one second, a value known as FEV1. Grip strength was quantified with a handgrip dynamometer and then normalized to body weight to create the relative grip strength metric, which corrects for the fact that heavier people can produce more absolute force without necessarily being stronger for their size. Metabolic syndrome was defined using consensus criteria, requiring the presence of at least three of five risk factors: elevated waist circumference, high triglycerides, low HDL cholesterol, elevated blood pressure, and high fasting glucose.

Among the 353 participants, 115—about one in three—met the definition of metabolic syndrome, a prevalence consistent with national estimates for this age group. The researchers then divided pulmonary function and relative grip strength into tertiles, or thirds, and used multivariable logistic regression to estimate the odds of metabolic syndrome across these categories. They also built four joint exposure groups combining high and low pulmonary function with high and low relative grip strength, using the theoretically healthiest combination as the reference point.

The initial findings looked striking. In minimally adjusted models, there was a significant linear trend between FEV1 tertiles and metabolic syndrome: the lower a person’s lung function, the higher their odds of having the condition. That result seemed to confirm the idea that even within the normal, lung-healthy range, subtle decrements in breathing capacity track with metabolic dysfunction. For a moment, the data appeared to support the notion that spirometry could serve as an early-warning system for metabolic risk in older adults with no diagnosed respiratory disease.

But when the team added relative grip strength to the statistical models, the pulmonary signal largely evaporated. The linear trend between FEV1 and metabolic syndrome was attenuated to the point of statistical non-significance once muscle strength was accounted for. In contrast, relative grip strength showed a significant linear trend with metabolic syndrome across every model the researchers tested, even when adjusting for lung function, with P values below 0.001. In other words, the apparent lung-metabolism connection was not independent at all—it was riding on the coattails of strength.

The joint analysis drove the point home with almost viral clarity. Compared with older adults who had both high pulmonary function and high relative grip strength, those with low lung function but strong grips showed no meaningful elevation in odds, with an odds ratio of 1.13 and a confidence interval spanning 0.56 to 2.26. But participants with high lung function yet weak relative grip strength had more than three times the odds of metabolic syndrome, at 3.27 (95 percent CI 1.70 to 6.27). And those unlucky enough to have both low lung function and low grip strength fared worst of all, with an odds ratio of 4.50 (95 percent CI 2.20 to 9.22)—a more than fourfold increase in the odds of metabolic syndrome compared with their fitter peers.

The technical interpretation hinges on the concept of confounding. Lung function and grip strength are correlated with each other, because both decline with age, physical inactivity, systemic inflammation, and sarcopenia—the progressive loss of muscle mass and strength. When two exposures travel together, a statistical model that includes only one of them will attribute to it the effects of the other. FEV1, it turns out, was acting as a proxy for overall physical capacity rather than as an independent metabolic risk factor. Once the model was told how strong each participant was relative to their body weight, the lungs had nothing left to say about metabolic syndrome.

Why would relative grip strength be so dominant? The answer likely lies in skeletal muscle’s role as the body’s metabolic engine. Muscle tissue is the primary site of glucose disposal, consuming the majority of circulating blood sugar after meals, and it secretes myokines—signaling molecules released during contraction—that influence inflammation, insulin sensitivity, and fat metabolism. A weak grip relative to body weight signals a low muscle-to-mass ratio, meaning less metabolic machinery to handle glucose and lipids. Low relative strength also often reflects higher body fat for the same weight, compounding the metabolic burden. Grip strength, cheap and quick to measure, has increasingly been promoted as a single-number biomarker of healthy aging, and this study strengthens that case.

The authors caution that their findings come from a cross-sectional design, which captures a single moment in time and cannot establish whether weak grip strength causes metabolic syndrome or vice versa. The cohort was also limited to lung-healthy older adults in the US Midwest, so the results may not generalize to people with respiratory disease or to other populations. Still, the practical message is compelling: for older adults with healthy lungs, a spirometry result in the low-normal range should not be read as a metabolic warning sign on its own. Instead, clinicians and patients alike may do better to focus on the grip test—a measure that costs pennies, takes seconds, and, according to this study, tells a far more honest story about metabolic risk than the breath does.

Subject of Research: Joint associations of pulmonary function and relative grip strength with metabolic syndrome in lung-healthy older adults

Article Title: The joint associations of pulmonary function and relative grip strength with metabolic syndrome in lung-healthy older adults: Cross-sectional findings from the Physical Activity and Aging Study

Article References: Saavedra, J. M., Lefferts, E. C., Downer, B., & Lee, D.-C. (2026). The joint associations of pulmonary function and relative grip strength with metabolic syndrome in lung-healthy older adults: Cross-sectional findings from the Physical Activity and Aging Study. PLOS Aging and Health, 1(2), e0000027. https://doi.org/10.1371/journal.page.0000027

Image Credits: AI Generated

DOI: 10.1371/journal.page.0000027

Keywords: metabolic syndrome, grip strength, pulmonary function, FEV1, spirometry, aging, older adults, sarcopenia, cross-sectional study, logistic regression, physical activity, muscle strength