https://www.nytimes.com/2019/04/03/well/move/heart-health-swimming-running-exercise.html?keplerid=249784550&dclid=CLKr1pqJoOMCFUzzyAodVG0Crw
In theory, those differences should allow blood to move from and back to the runners’ hearts more rapidly than would happen inside the swimmers’.
But these differences do not necessarily show that the runners’ hearts worked better than the swimmers’, says Jamie Burr, a professor at the University of Guelph and director of its human performance lab, who conducted the new study with the lead author, Katharine Currie, and others.
Since swimmers exercise in a horizontal position, he says, their hearts do not have to fight gravity to get blood back to the heart, unlike in upright runners. Posture does some of the work for swimmers, and so their hearts reshape themselves only as much as needed for the demands of their sport.
The findings underscore how exquisitely sensitive our bodies are to different types of exercise, Dr. Burr says.
They also might provide a reason for swimmers sometimes to consider logging miles on the road, he says, to intensify the remodeling of their hearts.