It turned out, to no one’s surprise, that the athletes, whether runners or swimmers, enjoyed enviable heart health. Their heart rates hovered around 50 beats per minute, with the runners’ rates slightly lower than the swimmers’. But all of the athletes’ heart rates were much lower than is typical for sedentary people, signifying that their hearts were robust.
The athletes also had relatively large, efficient left ventricles, their echocardiograms showed.
But there were interesting if small differences between the swimmers and runners, the researchers found. While all of the athletes’ left ventricles filled with blood earlier than average and untwisted more quickly during each heartbeat, those desirable changes were amplified in the runners. Their ventricles filled even earlier and untwisted more emphatically than the swimmers’ hearts did.
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.
Source : Nytimes