I was in the same position as you about
10 months ago when I finally got into remission for the first time in ages. Having been very fit before my diagnosis back in 2003 I really wanted to get back into shape. I had been going out on my bike for the previous year when I could, which would vary from every couple of days to once or twice a month, so I had at least been keeping as active as I could. In March I started playing squash a couple times a week and going to a gym, I would use the bike for 30 mins to start with followed by some weights. Since then I've been going to the gym 6-7 days a week spending a hour plus on the bike (hard cycling), then 45 mins or so on weights, increasing the weight considerably. I even managed a 10 mile run on Sunday (I ached on Monday as I hadn't been for a run for over 10 years!) I would say I'm close to the fittest I've ever been, the only annoying thing is food. I find red meat especially non processed doesn't agree with my UC, this limits the amount of protein I'm getting so although I'm doing loads of exercise and weights and have always been slim I've actually lost a little weight and not bulked up at all.
The best advice I could give would be to stick to an exercise you can do on your own to start with, so you can set your own pace. You also need to make sure you're eating the right amount of the right foods. I found energy drink tablets really useful, especially to start with when I was feeling a lack of energy.
If anyone has any advice on protein and protein suppliments your comments would be welcomed.
Diagnosed 2002, had first endoscopy on my 27th birthday!!
Preds x 5mg a day
Azathiaprine x 200mg a day
In remission since November 2007 - best since diagnosis