> Extreme long-distance running can produce recurrent gastrointestinal stress, including splanchnic hypoperfusion, mucosal injury, and post-exercise rectal bleeding, but its relationship to colorectal neoplasia is unclear.

> In this endurance-runner sample, advanced adenomas were observed at a prevalence of 15.0% overall. Compared with historical screening benchmarks, prevalence appeared higher, supporting further evaluation of colorectal neoplasia risk in endurance runners.

I wonder if there's also an increased risk with weightlifting? Squats in particular can put a lot of stress on the abdomen and result in haemorrhoids and so on, although I suppose it is much less chronic than with running.