Recent Studies on the Subject of Training

1) Weight Training Suppresses Myostatin: Med Sci Sports Exerc, 36: 787-793, 2004)
Myostatin is the protein in the body that limits muscle growth. Cattle that are bred without the myostatin gene grow enormous amounts of lean muscle with very little body fat, even in the absence of exercise. Weight training in humans seems to suppress expression of the myostatin gene, which allows the body to build muscle in response to the training. Several new supplements claim to even further suppress myostatin, but none have yet been tested in a labratory setting. The real future is in creating a virus that can deactivate myostatin -- a development that is no more than five years away from being reality.

2) Weight Training Is Crucial for Weight/Fat Control: Med Sci Sports Exerc, 36: 973-982, 2004)
It's only in the last few years that weight training has gained status in efforts to lose body fat. Previously, it was assumed that aerobic exercise and a low-calorie diet was enough. Some studies have shown that weight training with aerobics is the best combination for reducing abdominal fat (J Physiol Anthropol, 22: 129-135, 2003). The study did not show why this approach worked, however. A new study by Danish researchers demonstrates that fast-twitch muscle fibers (strength and power fibers) are used in weight training, while slow-twitch fibers (endurance fibers) are used in aerobics. The study showed that fast-twitch fibers burned more calories after training when slow-twitch fibers were depleted of glycogen during aerobic exercise.

Although some people prefer to do their aerobics before weight training, I recommend weight training first, which will also use up glycogen stores, followed by aerobic training. In this scenario, fat will be the primary energy source for the aerobic session.

3) Volume and Intensity Should Vary for Maximum Muscle Growth: Med Sci Sports Exerc, 36: 965-972, 2004)
Many trainees use the same set and rep schemes day in and day out, year after year, and wonder why they aren't making any progress. The body has two basic muscle fiber types (this isn't really true, but it gets very complex very quickly if all fiber types are addressed): type-I fibers are slow-twitch and are endurance fibers; type-II fibers are fast-twitch and are strength and power fibers. Type-I fibers grow with high reps (12 and above) and type-II fibers grow with lower reps (1-6). Consequently, most trainees use the standard 3 sets of 8-12 reps for each exercise in an attempt to get the best of both worlds.

The problem is that type-I fibers don't really grow very big or very fast. Type-II fibers can grow larger and, if trained correctly, can grow much faster. When type-II fibers are fatigued, type-I fibers pick up some of the slack.

Vary your training, either within a given workout (3-6 heavy sets for low reps followed by a high rep set) or within a training week (a heavy day and a light day for each muscle group). Making your muscles grow is not as simple as just lifting some weights and eating some extra protein -- there is a science to muscle growth, and understanding the science (or hiring a trainer who does) will give you much better results in the gym.