Swimming matched running for fitness gains but delivered greater heart growth and more favorable molecular changes, making it potentially more beneficial for cardiovascular health.
For decades, swimming and running have been considered two of the best forms of aerobic exercise for cardiovascular health.
But new research suggests they may not strengthen the heart in exactly the same way. In a study using an animal model, scientists in Brazil found that swimming produced more extensive changes in heart structure and function than running, pointing to distinct biological pathways through which different forms of exercise shape cardiovascular health.
Researchers at the Federal University of São Paulo (UNIFESP) discovered that swimming was more effective at promoting healthy heart growth and increasing the force with which the heart muscle (myocardium) contracts.
“Swimming and running are two excellent ways to improve cardiorespiratory health and protect the heart muscle, but we wanted to know if one could be even more beneficial than the other. We found that, although both increase respiratory capacity, swimming goes a step further by combining functional and molecular adaptations that make the heart stronger and more efficient,” says Andrey Jorge Serra, a professor at UNIFESP and coordinator of the study supported by FAPESP.
The findings, published in Scientific Reports, showed that swimming triggers stronger changes in microRNAs involved in key heart adaptations. These include heart cell growth, the development of new blood vessels (angiogenesis), protection against cell death, regulation of contractile function, and responses to oxidative stress. The effects were more pronounced than those observed with running.
How Swimming Influences Heart MicroRNAs
MicroRNAs are molecules that regulate the expression of messenger RNAs, which are responsible for protein synthesis.
“Although several studies had already examined the expression of microRNAs regulated by aerobic training in general, little was known about expression patterns when swimming and running were compared in the same experimental setting. Therefore, this study reveals that there’s a distinction in cardiovascular effects between these two modalities,” says Serra.
For the experiment, mice followed an eight-week training program that included 60-minute exercise sessions five days per week. The animals were divided into three groups: a sedentary group, a running group, and a swimming group. Because swimming and running are fundamentally different activities, researchers compared them based on relative exercise intensity rather than speed. Intensity was measured using maximum oxygen consumption (VO₂ max), a standard indicator of the body’s ability to capture, transport, and use oxygen during physical activity.
Swimming Produces Greater Heart Growth
Both forms of exercise improved fitness to a similar degree. VO₂ max increased by more than 5% between the beginning and end of the training period in both exercise groups. However, only swimming produced significant structural changes in the heart, including increases in overall heart mass and left ventricular mass. Running did not result in meaningful differences compared with sedentary animals.
“People’s choice of sport depends largely on personal preference, aptitude, and enjoyment. But our results show that swimming may have a special impact in situations involving myocardial recovery, cardiac rehabilitation, and above all, scientific research. This is also relevant because studies on aerobic exercise often use running and swimming interchangeably, and we now know that the effects aren’t the same,” Serra explains.
Researchers conducted a range of tests before and after the training program to assess cardiorespiratory capacity, physical fitness, and the structure and function of the heart and myocardium.
Molecular Mechanisms Behind Cardiac Hypertrophy
The team also examined gene expression and protein signaling pathways linked to physiological cardiac hypertrophy, a healthy form of heart enlargement caused by exercise. In addition, they investigated the molecular mechanisms used to identify regulatory microRNAs.
“Although we don’t yet know why this change occurs at the molecular level, of the microRNA, we were able to delve deeply into and investigate the molecular pathways that control physiological hypertrophy,” the researcher adds.
Reference: “Swimming is superior to running in inducing physiological cardiac hypertrophy and enhancing myocardial performance” by Amanda Yoshizaki, Ednei Luiz Antonio, Luis Dos Santos, Mariana Teixeira dos Santos, Flavia Leticia Martins, Regiane Santos Feliciano, Jose Antonio Silva Junior, Brunno Lemes de Melo, Danilo Sales Bocalini, Paulo José Ferreira Tucci, Adriana Castello Costa Girardi and Andrey Jorge Serra, 29 January 2026, Scientific Reports.
DOI: 10.1038/s41598-026-36818-2
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