Lighten Up!

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Does training with light weight trump heavy weight for building muscle?

You've seen them in every gym.

Those guys who grunt and groan as loud as they can while loading up the bar with as many plates as possible to eke out a few reps with very poor form. You see them training with as much weight as possible every time they're in the gym, but they won't make much progress if they continue to train this way.

I have some news that will ruin their day: Training with much lighter weight for far higher reps will actually help them build more muscle than heavy and hard training.

Sure, they'll laugh and shrug it off. After all, they care more about how impressed you are with the weight they're barely moving than getting real results. But if you're reading this, I know your first priority is getting unreal results. So read on to learn the science behind how light weights can help you grow more muscle.

Repetition Maximum Continuum

In the world of strength-training science, rep ranges are categorized into what's known as a "repetition maximum continuum."

This breaks down the rep ranges into three main categories:

1) Muscle strength

2) Muscle hypertrophy (muscle growth)

3) Muscle endurance

Research and years of training have previously shown that the rep range of 1-6 per set is best for increasing muscle strength; 7-12 reps per set is best for increasing muscle growth; and reps of 12 and higher are best for increasing muscle endurance. This sounds solid based on what we know about muscle physiology and the energy systems used during these types of workouts, as well as the results that athletes have seen over the years training this way.

So most guys end up training in the 6-8 rep range, maybe going as high as 10 reps occasionally, as this is the rep range that allows them to look and feel the most impressive in the gym -- hoisting as much weight as they can, but doing just enough reps to stimulate muscle growth.

Theoretically, this sounds like the smartest plan based on the repetition maximum continuum. It's pure science, right? But alas, as it often happens in science, there's new research that turns the traditional way of thinking upside down.

The Size Principle

Another fact that strength scientists have learned in the laboratory is that muscles are recruited (or called to contract) from smallest to biggest.

This is known as the "size principle." There are two main types of muscle fibers: slow twitch and fast twitch. Slow-twitch muscle fibers are those with the most endurance, but they're also the smallest and weakest. The fast-twitch fibers are those that have less endurance, but the most strength and power and the ability to grow the biggest.

When you pick up a weight and do a biceps curl, the slow-twitch muscles fibers in the biceps are recruited first to lift the weight.

If the weight is too heavy for the few slow-twitch muscle fibers that are recruited, the brain signals the rest of the slow-twitch fibers available in the biceps to assist their pals. If the weight is still too heavy for them, the brain starts calling on some of the bigger fast-twitch fibers in the biceps to assist those small, weak slow-twitch muscle fibers.

If the weight is still too heavy, the brain calls in the rest of the big and strong fast-twitch fibers to assist and the weight is curled up successfully. Of course, this all occurs in a matter of microseconds.

If you curl the maximum weight that you can lift for one rep, then just about every single muscle fiber from slow to fast will be recruited to lift that weight.

However, when you pick up a weight that you can curl for 20 reps, you may only recruit the slow-twitch muscle fibers because the weight is so light that the fast-twitch fibers don't even need to be bothered. Since the fast-twitch fibers are the ones that grow the biggest and strongest and the slow-twitch fibers need to stay small for maximal endurance, it has been assumed that to really build maximal muscle size, the weight must be heavy enough to recruit the fast-twitch muscle fibers.

Now back to that weight that you could complete 20 reps of curls with: Yes, when you do the first few reps you are only recruiting the slow-twitch muscle fibers. But as the reps continue and those slow-twitch muscle fibers fatigue, the brain starts calling on more and more of the bigger fast-twitch fibers with each and every rep completed.

If you take that 20-rep set to absolute muscle failure -- the point at which you can't complete another rep -- you recruited the same amount of fast-twitch muscle fibers as you did when you used a weight that limited you to one rep.

This is the real key to how higher rep sets performed with lighter weight may be better for muscle growth than doing fewer reps with heavier weight: training to muscle failure.

While recruiting the maximum number of fast-twitch muscle fibers may be crucial for muscle growth, there appears to be other factors involved.

After all, if muscle growth was only about recruiting fast-twitch muscle fibers, the best way to grow would be to always lift a weight that limits you to one rep. Yet, as we all know, that's not the best way to grow muscle. In fact, that's not even the best way to increase muscle strength. This is due to the fact that metabolic stress is also important for both muscle growth and muscle strength.

Metabolic Stress

Metabolic stress is created within the muscle when byproducts accumulate from the biochemical pathways used in the muscle cells to produce the energy required to lift the weight.

These byproducts signal other chemicals in the muscle, such as insulin-like growth factor-I, to come in and induce muscle hypertrophy. The byproducts even signal other chemicals to be released from other areas of the body.

For example, growth-hormone levels increase as levels of the metabolic byproduct lactic acid rise. These may... Subscribe to read more!

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WHO IS JIM STOPPANI?

Jim Stoppani received his doctorate in exercise physiology with a minor in biochemistry from the University of Connecticut. Following graduation, he served as a postdoctoral research fellow in the prestigious John B. Pierce Laboratory and Department of Cellular and Molecular Physiology at Yale University School of Medicine, where he investigated the effects of exercise and diet on gene regulation in muscle tissue. He was awarded the Gatorade Beginning Investigator in Exercise Science Award in 2002 by the American Physiological Society.