Swimming Enhances Heart Growth and Molecular Benefits More Than Running

Researchers at the Federal University of São Paulo (UNIFESP) have demonstrated that swimming results in more pronounced heart growth and molecular adaptations compared to running, even though both exercises yield comparable enhancements in cardiorespiratory fitness.

The study, published in Scientific Reports, involved an eight-week training program with mice undergoing 60-minute sessions five days per week. The animals were assigned to sedentary, running, or swimming groups, and exercise intensity was standardized by measuring maximum oxygen consumption (VO₂ max) to ensure equal effort across activities.

Distinct Cardiovascular Effects of Swimming and Running

Both swimming and running increased VO₂ max by more than 5%; however, only swimming caused significant structural heart changes, including increases in total heart mass and left ventricular mass. Running did not produce meaningful differences when compared to sedentary controls.

Professor Andrey Jorge Serra, who coordinated the study at UNIFESP, explained that swimming combines functional and molecular adaptations that enhance heart muscle strength and efficiency beyond the improvements seen with running.

MicroRNA Regulation and Heart Adaptations

The investigation revealed that swimming triggered stronger modifications in microRNAs, which regulate messenger RNA expression and protein synthesis essential for heart cell growth, angiogenesis, protection against cell death, contractile function, and oxidative stress responses. These molecular effects were more substantial than those induced by running.

Serra pointed out that although previous studies have examined microRNA expression in aerobic training generally, this research is among the first to directly compare swimming and running within the same experimental framework, uncovering distinct cardiovascular impacts between the two exercise types.

Investigating Molecular Pathways of Cardiac Hypertrophy

The researchers also analyzed gene expression and protein signaling pathways involved in physiological cardiac hypertrophy, a healthy form of heart enlargement prompted by exercise. Their focus was on molecular mechanisms regulating microRNAs, although the exact causes of the molecular differences observed remain unclear.

Serra highlighted the importance of these findings for myocardial recovery and cardiac rehabilitation, as well as for scientific research, especially since aerobic exercise studies often treat running and swimming interchangeably despite their distinct effects on the heart.