I've pretty much always been into exercise since youth, of some form or another. I used to ride or walk to school, and well... everywhere in those years. I got lazy for a period when getting my first car, though then got into gym and me and a mate did that together for years several times weekly. It was our guy time outside of work and women, basically. Then I fell out of exercise for a couple of years, then military... so back into it. Then I fell out of it after discharge for a couple of years, then I got back into it, riding, running, walking... and its been a bit that way since.
I love to bicycle, walk and whilst I like running, it is just getting hard to do on my knees due to the military punishment knees endure. Walking fast is easy without any pain... running... the knees can get sore without adequate bounce below me (i.e. springy treadmill).
When I put on weight during slack times, depression kicks my arse... so its pretty much always in my own best interest to simply keep exercising regularly nowadays. Never had that issue prior to PTSD, though I do after the fact, nowadays.