Can too much exercise kill you? A systematic review of the risk of a cardiovascular event or death from long term strenuous exercise.

A considerable number of studies have highlighted that engaging in physical activity (PA) improves health and reduces risk of mortality. But is there a limit? Some evidence suggests a U-shaped exposure-response in which the protective benefits of strenuous exercise eventually diminish (at some point) and the risk of a cardiovascular event or death increases, thereby questioning a linear association between exercise volume, intensity, and cardiovascular events/mortality. This review evaluates the evidence and critically appraises studies assessing whether strenuous exercise is associated with increased cardiovascular-related events from an epidemiological perspective. After a comprehensive literature search, 1,908 records were identified; 1,068 remained after deduplication. Title/abstract screening excluded 950 records; 66 full texts were assessed; 14 studies were included for critical review. Two independent assessors appraised study quality and risk of bias, focusing on exposure and outcome measurement, confounder control, and whether timeframes and follow-up were adequate to observe associations. Evidence supporting a U-shaped exposure-response was limited. No study achieved the highest quality rating. Common limitations included inconsistent intensity classification, absence of repeated exposure measurement, inconsistencies with outcome measures, insufficient follow-up to capture long-term effects, and incomplete adjustment for key confounders. The current evidence supports the benefits of regular PA, including strenuous activity, with benefits appearing to plateau at very high doses. Further rigorous epidemiological research with repeated exposure measures, standardised outcomes, adequate follow-up, and more robust control for confounding is needed.