Have you resolved to exercise more this year? Or perhaps you have instructed your patients to do so? Recent data published in the British Medical Journal have demonstrated that Olympic athletes live an average of 2.8 years longer than a control population.
One of the most important health benefits of exercise is a decreased resting heart rate. It has been observed among mammals, and to a lesser extent, in birds and reptiles, that the total number of heartbeats in a lifetime is roughly equal among all species. For example, a shrew has a very high heart rate and short lifespan, and a blue whale has a low heart rate and long lifespan.
One interpretation of this observation is that lifespan is limited by compliance of the aorta. I like to think of compliance as the opposite of stiffness. Aortic compliance is crucial for dampening the pulsing flow of blood as it is pumped out by the forcefully contracting heart muscle. Compliance makes blood flow in a more uniform manner in the branches of the aorta.
Aortic compliance is principally due to the protein elastin. Like any material subjected to repetitive stress, elastin molecules fatigue and fracture with repetitive stress, making the aorta stiffer. Loss of aortic compliance is an early event in the development of atherosclerosis. I have provided a detailed description of the hemorheologic-hemodynamic theory of the cause of atherosclerosis elsewhere, and there is also a short animation on this website that may be helpful in visualizing atherosclerosis as a protective adaptation response to stress.
Unfortunately, as noted by the prominent experts Nichols and O’Rourke in their well-recognized textbook McDonald’s Blood Flow in Arteries, many physicians have been reluctant to consider physics and engineering principles such as material fatigue in investigating the root causes of diseases. I’m not sure if this is because of a lack of physics knowledge or a bias towards biochemistry.
Let’s consider the idea of aortic compliance more deeply for just a moment. If material fatigue plays a role in the degeneration of the cardiovascular system and aging, then too much exercise would prematurely wear out the aorta. This possibility is suggested by a recent editorial published in the medical journal Heart titled “Too Much Vigorous Exercise Can Damage Heart.”
As a health-conscious person, if I am interested in reducing my resting heart rate and maximizing lifespan—not training for Olympic competition, then I ought to keep in mind that even though intense exercise can feel great, moderation is ultimately the best course.
As noted in an editorial accompanying the aforementioned British Medical Journal report: “Although the evidence points to a small survival effect of being an Olympian, careful reflection suggests that similar health benefits and longevity could be achieved by all of us through regular physical activity.” After all, as stated by one of the founding fathers of modern medicine Sir William Osler, “Longevity is a vascular question.” For Further Reading: