Building muscle mass is one of the toughest tasks you can attempt. Okay, sainthood is probably harder, but not by a lot. Your body is an extremely efficient machine. It retains the amount of muscle mass that is required to comfortably perform your daily routine—no more and no less. Excess bulk takes a lot of energy to maintain—up to 50 calories a day per extra pound of muscle mass you add—and thousands of generations of evolution have taught your body that that's a waste of perfectly good nuts, berries, and animal flesh. So it adds muscle reluctantly, and sheds it willingly when you stop exercising.

Unfortunately, evolution couldn't have imagined a society in which high-quality protein is plentiful and people judge each other on the basis of quadriceps definition, biceps bulge and pectoral depth.

So if you're going to step into the weight room to build a body that flaunts the unnatural abundance of these times, there are only two rules you need to know:

Rule #1: Lift heavier weights.

"I see people in the gym doing the same thing day in and day out," says Jose Antonio, Ph.D., C.S.C.S., an exercise physiologist at the University of Nebraska-Kearney, "Doing any one thing for a prolonged period is a waste of time." The problem is that once you've done the same exercises with the same weights for a period of time—a month or two, say—your body has made all the changes it's going to make in response to those exercises. In other words, it's not going to add muscle.

To break this holding pattern and build more muscle mass, Antonio suggests a three-phase approach.

Phase One: Be an organization man (or woman). Organize your workouts into three periods, each lasting a month to six weeks: First, go for rapid muscle growth. Do strength training workouts with progressively heavier weights. That means, on most exercises, do 3 sets of 6 to 10 repetitions, using enough weight so that your muscles are fatigued on the last rep.

Phase Two: Next, do a strength cycle, and do power lifting-type workouts with much heavier weights. (As with all lifting programs, be careful not to overdo it, and always have a spotter when using maximal free weights.) Thoroughly warm up with at least 15 minutes of light cardio exercise and stretching, then do 4 to 5 sets of 3 to 5 repetitions of exercises like squats, deadlifts, and bench presses.

Phase Three: Do a few weeks of "cutting up," in which you lift lighter weights—go for 3 sets of 12 to 15 repetitions, and employ supersets (going from one exercise to another without taking a rest in between) and other high-intensity tactics. Add more cardio exercise, and watch your diet more carefully. This doesn't add new muscle or strength, but it sure lets you see what you've spent the previous months building.

Rule #2: Eat the right foods at the right times.

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