Cardiovascular Issues

Can Too Much Exercise Harm the Heart?

I was once asked: "How 'healthy' is the high intensity cycling that I've been doing? I'm over 50 and by high intensity I mean continuous effort at 85-90% HRMax with touches of 100% HRMax."

In 2015, the answer was summarized in this NYT article sating that .."assuming no family or personal history of heart disease, there was ... no evidence...there is a level of exercise that is dangerous or too much for a normal, healthy person."

Although this remains true, there is some evidence for an upper limit for cardiac-healthy exercise. The graph of benefits versus exercise volume may not plateau, but instead start to drop off as the extremes are reached.

A few pertinent articles:

Findings of diverse patterns of myocardial scarring (fibrosis) in lifelong, veteran endurance athletes suggests that cardiac scarring may be associated with more years spent training, number of competitive marathons, and ultraendurance (>50 miles) marathons completed.

The paper Risk of arrhythmias in 52,755 long-distance cross-country skiers: a cohort study documents that in cross-country skiing, a faster finishing time and a high number of completed races was associated with a 30% higher risk of developing a cardiac arrhythmia.

A study from 2012 revealed that competitive level aerobic events were associated with transient cardiac muscle dysfunction. To quote ".....chronic training for and competing in extreme endurance events such as marathons, ultra-marathons, ironman distance triathlons, and long distance endurance bicycle races, can cause transient reductions in right ventricular ejection fraction and elevations of cardiac biomarkers, all of which return to normal within 1 week.""

These short term functional changes were noted again in this paper from 2026. Researchers often observed "cardiac fatigue" after prolonged endurance events - functional changes that included reduced right ventricular performance (pumping less blood per beat) and transient blood biomarker elevations. But once again these changes resolved quickly and were not linked to permanent structural damage.

They concluded these short-term changes should be considered an acute physiological (functional) response to the event rather than a pathological (tissue harming) process. And current evidence suggests these cardiac effects from marathon running are generally transient and reversible. There was little support for the idea that endurance exercise at this level led to lasting heart damage in healthy individuals and the broader body of research continues to support regular endurance exercise being associated with cardiovascular benefit and potential long term risks are uncommon and likely limited to predisposed individuals.

So what is the answer to the reader's question?

There is no solid data to support an upper limit for an amount of aerobic exercise beyond which harmful effects begin to accumulate- assuming no family or personal history of cardiac disease or sudden death.

There is no evidence that short term, high level exertion such as 30 to 60 second intervals is harmful and also no sound evidence that intervals longer than this add benefit to cardiovascular fitness.

There are two potential health risks from high intensity cycling - Musculoskeletal (or overuse) injuries and cardiovascular.

The musculoskeletal injuries are known to all of us who exercise and participate in aerobic sports. Overuse leads to injury. The cure here is to listen to your body, and if it hurts when you are using it, decrease your activity level.
The cardiovascular risks, if any, appear to be from repeated stress at the ultraendurance event level. (Pushing through the pain, as it were.) Although acute stress might cause some modest cardiac muscle injury (and leakage of muscle enzymes into the blood where they can be measured) this heals within a few days, and only with repeated injury/healing/injury does scarring appear to be a risk.

Bottom Line? Pushing your limits (within reason) is not harmful to your health. Any cardiovascular risk only appears to be a possibility if you move to recurrent ultra events. If yo are worried,

Do intervals to improve your aerobic fitness.
Do long rides just once or twice a week to get your musculoskeletal systems in shape for long rides.
And most importantly, as you train, listen to your body.

If it hurts (bones, joints, butt) when you use it, reassess and modify your program.
If your legs are tired as you do start intervals, take a day off, do some easy spinning (with light interval stress if you feel compelled) and come back ready for another try the next day.

The Paradox of Exercise

Aerobic athletes have lower rates of mortality from cardiovascular disease. To quote "Elite endurance (aerobic) athletes and mixed-sports (aerobic and anaerobic) athletes survive longer than the general population, as indicated by lower mortality and higher longevity with lower cardiovascular disease mortality the likely the primary reason for their better survival rates. On the other hand, there are inconsistent results among studies of power (anaerobic) athletes."

The "paradox of exercise" is a low cardiovascular mortality in endurance athletes who have high rates of coronary artery disease (plaques) on imaging studies.

Calcified plaques tend to be stable while non calcium plaques often rupture leading to an acute blockage of the coronary artery and in turn a cardiac event. Perhaps endurance athletes have a more favorable ratio with more calcified plaques and fewer unstable plaques. But this study shows that is not the case. Not only do lifelong endurance athletes have more coronary plaques than fit and healthy individuals with a similarly low cardiovascular risk profile, they have a similar ratio of stable versus unstable plaques as a group with healthy lifestyles.

So the search continues for an explanation for the paradox of more coronary disease but lower cardiovascular mortality. Possibilities such as (my ideas here) that these athletes have better collateral circulation and are thus better able to withstand an acute obstruction of one of the larger coronary arteries. Or perhaps some other factor that improves the stability of their uncalcified plaques.

All questions and suggestions are appreciated and will be answered.

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