Cardiovascular damage resulting from chronic excessive endurance exercise

Exercise is medicine — but this review asks the uncomfortable question of whether there’s such a thing as too much, specifically for the extreme endurance athlete.

Drawing on observational human data, animal studies, and case reports, the authors describe a possible dark side to chronic high-volume endurance training: patches of cardiac fibrosis (scarring), arterial stiffening, a higher burden of certain arrhythmias like atrial fibrillation, and even elevated coronary calcium in some lifelong endurance athletes. The proposed shape is a U-curve — large benefits from moderate activity, with diminishing or even negative returns at the extremes.

The practical takeaway is calibrated, not contrarian: for the vast majority, more activity is better and the message remains “move more”; the caution applies to the small population doing marathon-level volumes for decades. The resistance comes from endurance-sport culture invested in “more is always better.”

We rate the evidence low: a thought-provoking review, but built largely on observational and mechanistic data with speculative leaps, and the senior author is a known advocate of exercise moderation. Its clinical significance is moderate and debated — an important hypothesis about exercise dose that shouldn’t be mistaken for a reason for most people to do less.