Amen livestrong.com: A little cardio is a five-minute warmup or jogging lightly for a mile on your way to the gym. A lot of cardio is running on the treadmill for an hour or doing a 45-minute aerobics class each time you’re at the gym. It’s good to do these things two or three times a week, but more often than that is too much. You’ll begin to lose muscle mass and enter a state of overtraining, which can have many adverse effects on your body and overall health.
I was doing an hour cardio and an hour strength training. Trouble was, i was burning off all the muscle I was trying to build. Now I do 20 mins cards (the walk to the gym) and 40 mins circuit/strength training. Now i’m buidling muscle.