Performance
Muscle mass, not sex, drives heart size and aerobic capacity in 294 adults
By Life and Health Today Staff, . Life and Health Today.
The cardiovascular differences between women and men, long treated as a fixed feature of biology, may largely reflect a simpler fact: men typically carry more muscle. When that gap is removed, the differences vanish. That is the central finding of a study published in Sports Medicine by Springer, also indexed on PubMed, involving 294 healthy adults aged 18 to 78.
What the researchers measured
The study enrolled 294 participants, half female, matched by age and physical activity level across the adult lifespan. Researchers measured body composition using dual-energy X-ray absorptiometry, a scanning method that separates fat from lean tissue. They also measured hemoglobin mass and blood volume, cardiac structure and function by ultrasound, blood pressure, and aerobic exercise capacity on a stationary bike with a metabolic cart tracking oxygen use.
Lean body mass, or LBM, is the weight of everything in the body except fat: muscle, bone, organs and fluid. It is the tissue that does metabolic work, meaning it consumes oxygen and drives the demand the heart must meet.
What they found
Across the full group of 294 participants, women and men differed on more than 90 percent of cardiovascular variables, including heart size, blood pressure, vascular resistance and aerobic capacity. That is the familiar picture. But when the researchers pulled out a subgroup of 70 individuals matched specifically by lean body mass, not one cardiac-related variable differed between women and men. Heart structure and function, blood pressure, systemic vascular resistance and aerobic capacity all aligned once muscle mass was held equal.
The regression lines describing how LBM relates to these variables ran at the same slope in both sexes. Women clustered toward the lower end of the overall range, men toward the upper end, but both sexes followed the same line. According to the study as reported by Sports Medicine, the sex dimorphism of the circulatory system, meaning the systematic differences between female and male cardiovascular profiles, "strongly associates with the metabolically active mass, rather than sex."
What this does and does not establish
This is an observational, cross-sectional study: it measured people at one point in time and found associations. It does not show that building muscle will change someone's cardiac profile, only that people with similar lean mass tend to have similar cardiovascular measurements regardless of sex. Whether the relationship is causal, and in which direction, would require a different kind of study.
The Sports Medicine paper was available only in part; the opening sections were accessible but the discussion and conclusions beyond the abstract were not, which means any limitations the authors stated in their full discussion are not captured here.
The study was conducted in healthy adults, so the findings may not extend to people with heart disease, low muscle mass from illness, or other clinical conditions.
Why it matters
Cardiovascular reference ranges, the numbers used to define what is normal for heart size or aerobic capacity, are routinely split by sex. If lean body mass is the underlying driver, those norms may be sorting people by the wrong variable. A woman with high lean mass and a man with low lean mass might both be misclassified against sex-based benchmarks that do not account for their actual muscle.
For anyone thinking about fitness across a lifetime, the finding adds to the evidence that preserving lean mass may bear on cardiovascular function as well as strength and metabolism. Whether acting on that changes outcomes is a question this study was not designed to answer, and a clinician who knows an individual's full history is the right person to interpret what it means for them.
Life & Health Today provides information for educational purposes only, not medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional.