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Does aerobic exercise really slow down muscle growth?

Almost everyone who invests time and effort in regular exercise wants a leaner, healthier, more attractive body. This means one of two things — more muscle or less fat. Usually, it's a combination of the two.

Of course, more muscle won't make a huge difference to the way you look if it's hidden under a layer of fat. That's one of the reasons aerobic exercise is so popular. After months — even years — of trying to gain as much weight and muscle as they can, many people turn to aerobic exercise in an attempt to shed the extra fat they've gained along the way.

Muscle growth

Some are concerned, however, that aerobic exercise will strip away the muscle they've worked so hard to build. One common belief is that anyone trying to build muscle should avoid aerobic exercise on the basis that it puts the brakes on muscle growth.

There are two main theories as to why aerobic exercise and weight training don't mix. According to theory one, your muscles have a hard time adapting to both resistance and aerobic exercise at the same time. The fact that changes in both the type and size of muscle fibers after a combination of weight training and aerobic exercise are different from those observed after resistance exercise alone provides some support for this idea.

Theory two contends that residual fatigue from the aerobic component of your program compromises your ability to "give your all" when you train with weights. Muscle damage and glycogen depletion are just two of the possible fatigue mechanisms with the potential to reduce the "quality" of your workouts.

Before you step on the treadmill or take a seat on the exercise bike, you need to know the full story about the effect of aerobic exercise on muscle growth. Here's what the current evidence shows.

The first and most important finding is...

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