This is a Q even I was wondering about:

Q: I have been told by a trainer that cardio performed over an hour is counterproductive to my weight-loss goals. But I prefer to cycle for a full two hours because I love it. I've lost 30 pounds with my cycling program so far. Any reason to cut back?

A: No. The new exercise guidelines say that people who want to lose weight should do more than the minimum amounts, upwards of an hour or more of exercise on most days. There’s no reason for people to cut back on their exercise program as long as they’re happy and healthy. Plus, your weight-loss plan is working! You’re losing weight and you enjoy the activity. Hard to argue with that.

Source: http://www.msnbc.msn.com/id/22325698/