No, Endurance Exercise Won’t Kill You (Part III)

If you’ve explored previous posts on my blog, perhaps you’ve stumbled upon parts I and II of “No, Endurance Exercise Won’t Kill You”, in which I make the argument (supported by evidence) that high-level endurance activity isn’t as harmful as some people like to think.

Read part I here.

Read part II here.

Those in the “anti-endurance” crowd base their claims on a handful of studies showing that people who engage in strenuous (some refer to it as excessive) endurance exercise throughout life have certain indicators of a increased cardiovascular disease (CVD) risk— coronary artery calcium, fibrosis (stiffening) of the heart, and other adverse structural cardiovascular changes.

On the other hand, we have buckets of evidence to the contrary — lifelong exercisers have a reduced risk of nearly every single disease…and live longer because of it.

This area of research is in its infancy, and we really need more data on the “extreme exercisers” to make firm conclusions on whether or not performing a high level of endurance activity may be harmful.

The argument is NOT that exercise is harmful, but rather, that it becomes deleterious at a certain level beyond what is “reasonable” by most standards. Elite endurance athletes, for instance, may experience a U-shaped curve of exercise benefits.

One problem with this research is that most, if not all of it, has been conducted in men. This is not trivial — we KNOW that there are sex-differences in the way men and women age, respond to exercise, and experience the risks of certain diseases like CVD. Findings in males can’t be assumed to apply to females.

Knowing how aging affects women is important, as is understanding how exercise might work to modify the cardiovascular aging process. Again — much data have been collected in men documenting the various changes that occur to the heart, blood vessels, and aerobic capacity with age. We also know, based on some recently-published data, that men performing extreme volumes of exercise have no more coronary artery calcium and no increased risk of CVD death vs. more moderate exercisers. Put another way, extreme exercise may pose no additional risk above and beyond “high” amounts of exercise — at least in men.

Newly published data recapitulate some of these findings, this time in a female cohort, using direct measures of cardiac health and function to demonstrate that exercising throughout one’s life can delay, if not completely prevent, the aging of the heart; even if the exercise is a bit “excessive.”

If we want to know how a near daily and lifelong exercise routine impacts cardiovascular aging, we need to find a group of women who have engaged in a high level of exercise their entire lives.

In this study, a group of 13 women were recruited who were either masters athletes who performed daily exercise or who were ‘committed’ athletes performing 4–5 sessions of exercise each week. These women reported having a consistent exercise routine for over 25 years on average.

For a comparison, the study recruited a group of untrained and age-matched older women (>60 years) and a group of untrained middle-aged women (35–59 years). These two groups allow us to see the effects of age on the heart (by comparing the younger group to older groups) and how exercise modifies the aging process (by comparing older trained to older untrained groups).

During aging, the heart undergoes changes that make it less compliant (less elastic) and stiffer, resulting in a decline in function and increasing the risk of disease. The goal of this study was to assess those changes and how they were affected by exercise.

Measures made in this study included assessments of left-ventricular function at rest and during exercise at a low, sub-maximal, moderate, and maximal intensity — how does the heart perform during exercise?

The size and mass of the left ventricle, stroke volume, and compliance (elasticity) of the heart muscle were analyzed using echocardiography, MRI, and catheter-based methods.

In addition to measures of the heart, maximal oxygen consumption (Vo2 max), body composition, blood and plasma volume, and blood pressure were also performed; providing a full suite of cardiovascular and metabolic health-related measures.

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Unsurprisingly, women in the lifelong exercise group weighed less and had a lower fat mass, but a similar fat-free mass (lean body mass) compared to the other two groups. They also had a lower resting heart rate (72 bpm) compared to the untrained groups (85 and 86 bpm for middle-aged and older groups, respectively) and a higher stroke volume — their stronger hearts pumped more blood during each beat.

The older trained women also had a significantly higher rate of oxygen consumption (Vo2 max) than the untrained groups; 34 ml/kg/min compared to just 21.5 ml/kg/min (older untrained) and 25.9 ml/k/min (middle-aged untrained). This result is very interesting, because we know that even with training, our aerobic capacity declines with age. Even though the trained women in this study were, on average, 20 years older than the middle-aged untrained group, they had a Vo2 max nearly ~31% higher.

During maximal exercise, cardiovascular measures were significantly improved in the older trained women. Cardiac output was higher, vascular resistance was lower, and arterial compliance was greater.

Cardiac output, heart rate, and other hemodynamic variables during exercise in each group. Carrick-Ranson 2020.

What about heart structure and function? The older untrained women in this study had a stiffer, less compliant left ventricle. The trained women had a heart that was not only less stiff than the older untrained women, but also healthier compared to the middle-aged untrained women. This shows us that a sedentary lifestyle and aging both contribute to a stiffening of the heart that is prevented through exercise training.

When it came to the size of the heart, trained women demonstrated a larger left ventricle mass index, indicating a bigger left ventricle as a result of all their endurance training.

Some of these results might seem obvious — of course women who exercise are going to have a higher exercise capacity, better body composition, and improved cardiovascular health compared to those who don’t engage in exercise.

But that wasn’t necessarily what the study was about. Rather, this investigation was designed to build upon the narrative discussed earlier that high level endurance activity might be detrimental. They wanted to find support (or a lack thereof) for this theory in a group of women who were actively and intensely engaged in exercise starting relatively early in life. If there were adverse effects of “extreme” exercise, these women would surely show it, as they’d been (over)doing it for 25 years or more.

(Side note, I abhor the term “extreme” or “excessive”, since these are arbitrary and relative terms. But…they’re what the studies are using…so we’re rolling with it)

Nevertheless, these results do not support the hypothesis that high-level endurance exercise leads to “athletes heart syndrome” — a constellation of “symptoms” including heart enlargement and electrophysiological changes that might lead to negative cardiovascular events.

The trained women in this study did have a larger left ventricle (about 16% greater than the untrained groups), however, they also had a larger chamber volume during relaxation — something known as left-ventricular end-diastolic volume. This means that the increased ventricle size was caused by outward remodeling of the heart and a “balanced” physiological adaptation to training. In fact, a larger left ventricle is one of the most well-known and consistent adaptations to endurance training that we know of; and it’s likely not harmful.

The authors note (and I agree) that some of the most interesting findings in this study are not that the older trained women “outperformed” the older untrained women, but also the group of untrained women who were nearly 20 years younger. Most measures of heart function and all measures of exercise performance were better in the women who exercised (66 years old on average) versus the younger group (44 years old on average) who engaged in very little to no exercise.

Exercise is that powerful.

The earlier in life that you can begin a consistent exercise routine, the greater chance you may have of preventing cardiovascular aging and drastically reducing your risk of developing CVD and many other diseases of aging. Exercise IS primary prevention.

And if you’re already at the age of the women in this study, evidence supports that exercise training can reverse many adverse age-related changes to the cardiovascular system. It’s one of the best-known ways to improve vascular function, reduce the stiffness of your arteries, and enhance heart health at any age.

As a runner, you can call me biased to endurance exercise, but really, nothing comes close in terms of improving cardiovascular healthspan and lifespan.

Humans were meant to move, evolved as endurance athletes, and I believe that our genetic hard-wiring still craves a nice, long run, and rewards us accordingly for taking action.

Study cited

Carrick-ranson G, Sloane NM, Howden EJ, et al. The effect of lifelong endurance exercise on cardiovascular structure and exercise function in women. J Physiol (Lond). 2020;598(13):2589–2605.

PhD candidate at the University of Florida — Science writing with a particular focus on exercise and nutrition interventions, aging, health, and disease.