As Pete said get a heart rate monitor, I aint too sure on what zone is what but when I am on the road bike I try and keep it in the 70% zone.
Running is your best bet IMO, since I started earlier this year I have noticed the gut has shifted quicker than it was doing before.
Keep an eye on the diet, good foods little and often, cut the treats for a week or 2, see if you notice a change there.