The Twisted Hearts of Runners

A study recently published in Frontiers in Physiology details the differences in heart structure between elite runners and elite swimmers. It turns out that runners’ hearts twist more, which could result in the more efficient pumping of blood. In a very simple model of exercised-induced demand, the primary requirement is that blood needs to be able to more quickly pumped through the body to deliver more oxygen and other compounds around the moving body. This is true regardless whether the exercise is rowing, running, swimming or some other exercise. This finding confirms what we have known to be true: that exercise-induced demands on the heart result in changes to the heart—and that different types of exercise result in different types of changes.

So, what, precisely, explains the differences between exercises? We don’t know yet. Runners tend to have a higher volume of blood overall. Perhaps this is the main explanation. Runners are mostly upright while swimmers are horizontal. Swimmers are surrounded by a denser environment (water rather than air). Would we observe similar differences between large enough groups of different kinds of swimmers? Do these (or other) differences occur between sprinters and marathoners? And can we invent devices that could detect such differences even in committed amateurs like me? All of these questions and others remain.

While these questions interest me from a professional perspective, I’m also personally interested in this study’s conclusions. I recently began training for a half-Ironman. Training for an endurance event has changed my body. Not just in terms of the visible alterations to musculature, body fat, and posture. My bones have stopped aching from to the harsh impact of running trails. My muscles become accustomed to the increased levels of lactic acid, cortisol, and other hormonal by-products of long swims, bike rides, and runs. But as a natural born skeptic, there’s always the sneaking suspicion that some of the changes I think I observe are really “all in my head.” So, it’s always nice when science can say, “No, this is real.” And, perhaps more importantly, “Here’s a way for you to use this knowledge to your advantage.”

Currie, K. D., Coates, A. M., Slysz, J. T., Aubry, R. L., Whinton, A. K., Mountjoy, M. L., … & Burr, J. F. (2018). Left ventricular structure and function in elite swimmers and runners. Frontiers in physiology, 9, 1700.

Reynolds, G., (2019). The Heart of a Swimmer vs. the Heart of a Runner. New York Times. 3 April.

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