A study at the University of Alabama supports this notion. The researchers had one group of men train each muscle group once a week for 3 months; another group performed the same number of total sets weekly but split them equally among three total-body workouts. The result? The men who worked each muscle more frequently gained 9 pounds of muscle -- 5 more than those who trained each muscle only once a week.
Repetition Ranges
"Go heavy or go home" is a common saying among bodybuilders. But, while it's crucial that you use a weight that provides a challenging load, the mantra is flawed. That's because muscle fibers can grow in two ways. The first is when the myofibrils -- the parts of the fiber that contain the contracting proteins -- increase in number and density. This type of growth leads to strength gains and can be accomplished by using heavy weights that allow only one to seven repetitions.
The second type of growth, however, occurs when your muscles are forced to contract for longer periods of time. Typically, this means using lighter loads that allow you to complete 12 to 15 repetitions. This increases the number of energy-producing structures within the fiber. So you don't get significantly stronger, but you do get bigger.
Using a repetition range that falls between the two causes a combination of both types of growth, but each to a lesser degree. And that's why Cosgrove uses all three repetition ranges. For instance, he might prescribe five repetitions of each exercise on Monday, 15 on Wednesday, and 10 on Friday. "It not only leads to better growth but also helps keep you from hitting plateaus," he says.
And indeed, in a 2002 study, Arizona State University researchers discovered that men who alternated their repetition ranges in each of three weekly training sessions gained twice as much strength as men who didn't vary their repetitions. To Cosgrove, it's just another case of a logical approach generating a logical result.