Of all things, rowing. It's a way to force myself to keep a consistent exercise routine because others depend on me to show up for each session, and given that my club has active members who are decades older than myself, I expect to continue doing it for as long as I can. It's especially great in a coxed boat with an experienced cox, it feels like the microphone wire is plugged directly into your brainstem so you completely outsource your executive functioning for two hours and respond to every call without even consciously parsing it.

And if you're after an adrenaline rush, a close race can teach you a whole new meaning of maximum heart rate.