Looking at overall mortality seems pretty limited. In my 20s I would sit at my desk all week, then go all-out on the weekend. Long bike rides, hikes, backpacking trips, etc. I had pretty good base-level fitness, but ended up with knee pain and minor injuries from strain and lack of flexibility. A near-daily gym habit has solved all of that for me. Seems like maintaining flexibility requires somewhat regular practice, and that's how you avoid injury.