https://academic.oup.com/eurjpc/advance-article/doi/10.1093/eurjpc/zwaf267/8128214
association between fitness and an outcome not expected to be causally affected is examined (e.g. random accidents
You can already see the flaw in their paper. A more fit person is more active. Going out more. Being exposed to more random accidents. The safest place to be is laying in bed all day. If you go out and run, if you go to the gym, any activity, you have more chance for random accidents...