Comment Nothing. (Score 1) 372
There's nothing you have to do during work hours, except keeping your workspace ergonomically sound. Standard desk, posture, good chair.
Then after work or before work, you spend an hour at the gym doing proper strength training and some cardio. I won't repeat other sites as there are many, but mainly dead lifts, squats, bench press, run-as-fast-as-you-can-a-mile. Just remember to keep improving yourself, log what you're doing, and always do a little more than before.
And that's it. If you get used to it it won't even be an hour, and you do it on alternate days too so it's not like it's every single day. That should not just make you fit, but probably one of strongest people around.