One of the keys to successful bodybuilding is the ability to add and maintain quality muscle and keep it. Unfortunately, you lose muscle at the expense of intense or large quantities of cardio! A bodybuilder with less than 10% body fat doesn’t have a lot of reserve to burn. There are a few exceptions - my freakishly strong baby brother just ran his first marathon in under 4 hours, and he still benches over 400 pounds - this is not usually the case however.

You burn too much glycogen during cardio sessions which go into the high intensity level, which would be defined as sessions which are closer to >80% of your maximum heart rate. You’re better off doing 20 minutes of cardio zone intensity then being done with it.

Balance your cardio intensity and duration with the addition of and retention of muscle, and as always, ensure you are eating adequate amounts of protein (.8 - 1.0 grams per pound of body weight for a bodybuilder) per day, spaced between at least six meals.