My man stays fit in a couple of ways. He uses a push chair and for the most part goes up ramps etc. under his own steam, he also does lots of upper body training. He is also very careful with his diet. A couple of things he does: limit his sugar and fat intake, eats no red meat at all and very few animal products in general (chicken, dairy, etc.). He eats several small meals a day instead of gorging himself once or twice. He is also careful not to pound down a big meal before he goes to bed, drinks lots of water, and takes vitamins.
This is a great community with a lot of great members and is potential a spot to get some good info on this topic!