Lighten Up!

May 21, 2012

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 all be important for increasing the process of muscle protein synthesis, which is ultimately how muscles grow. The best way to maximize metabolic stress is to do more reps.

Higher reps increase the amount of biochemical byproducts that are produced. So as long as you take that high-rep set to muscle failure, you'll recruit the same amount of fast-twitch muscle fibers as a heavier set for fewer reps. But you also induce greater metabolic stress. While all of this sounds good in theory, there's also research that supports this contention. Training with lighter weights is starting to sound a little more compelling, isn't it?

The New Research

The majority of the research on lighter weight/higher rep training comes out of the Exercise Metabolism Research Group at McMaster University in Canada.

The first work that grabbed the attention of strength scientists and well-read bodybuilders everywhere was a 2010 study the group published in the online science journal PLoS (Public Library of Science) ONE.

Trained men performed four sets of leg extensions using either a weight that limited them to 4-5 reps per set or a weight that allowed them to complete about 25 reps per set. They took all sets to muscle failure except for one additional group that used the 25-rep weight, but didn't go to full muscle failure.

When the men did the four sets with light weight for higher reps to muscle failure, muscle-protein synthesis of the quadriceps was elevated by as much as 60% more than when they did the 4-rep sets to failure. However, both the 4-5-rep and 25-rep sets taken to failure increased muscle protein synthesis far greater than the 25-rep sets not taken to muscle failure.

Going to Muscle Failure

A 2011 study by the same researchers looked at what happens to muscle-protein synthesis following heavy- or light-weight training when subjects consumed a protein shake 24 hours after the workout.

They performed four sets of leg extensions using either a weight that they could lift for about 4-5 reps or a weight they could lift for about 25 reps. Those doing the 4-5-rep sets took each set to muscle failure, while half of those doing the 25-rep sets went to muscle failure on all sets, while the other half didn't.

The researchers reported in the Journal of Nutrition that drinking a protein shake 24 hours after training to failure using either the heavy weight (4-5 reps per set) or the light weight (about 25 reps per set) significantly boosted muscle-protein synthesis higher than when they drank the same protein shake at rest or after weight training, but not going to muscle failure.

One trend that you should notice right away in these two studies is that the most critical factor in increasing muscle-protein synthesis, both immediately after training and for the 24 hours that follow, is to take all sets to muscle failure.

That's the only way to recruit all of the fast-twitch muscle fibers and instigate sufficient metabolic stress. This data finally shut up all those strength-training experts who say you shouldn't train to muscle failure, at least not on most sets. They claim that it leads to over-training and can actually interfere with strength and muscle growth.

No Excuses

Of course, the first thing you'll notice about most of these so-called experts is the fact that their upper arms barely measure 15 inches. If their lack of muscle mass doesn't tip you off, then that kind of nonsensical reasoning about muscle failure tells you right away that they don't understand the basics of muscle physiology and more specifically, never learned about the size principle. It also tells you that they haven't been paying attention to the newer research that has been conducted, such as these two studies.

As far as over-training goes, you have no worries about that as long as you follow a solid nutrition and supplement plan like the ones you find on my site.

Our ancestors used to be on their feet all day hunting and/or plowing the fields. They did intense labor for the majority of the day and only rested at night when the day was over. Do you honestly think after sitting on your ass all day at your desk job or in school that training intensely for 60-90 minutes is going to cause you to over train?! Get real!

This is just an excuse for those who don't want to put in the hard work it takes to build real muscle. They'll blame their genetics when really they should be blaming their poor work ethic and shoddy training techniques.

Bottom line: If you take anything home from this article, it's that you should be taking most, if not all, of your working sets to muscle failure, or close to it, for maximum muscle growth. The debate is over.

Another finding from these two studies is that training with lighter weight done for higher reps appears to be better at promoting muscle growth than heavier weight done for fewer reps.

Greater Muscle Growth?

But hold up: There are two problems with these two studies. The first is that these studies only measured muscle-protein synthesis. Yes, that is an indication that the muscle is in a heightened state of muscle growth. But they didn't measure actual muscle growth over time training these ways. They just looked at a snapshot from one workout. It's a pretty good snapshot, but it still doesn't prove that this will lead to greater muscle growth.

The second problem is that the heavy-weight sets were done with a weight that limited the subjects to just 4-5 reps. Even the most ego-maniacal bodybuilder typically doesn't train in this low of a rep range. So it really isn't a fair comparison of heavy weight versus light weight as far as what those terms mean for the average bodybuilder.

The McMaster researchers finally did a follow-up study to see just how well these light-weight, high-rep sets hold up for instigating real muscle growth compared to more realistic rep ranges.

They had subjects perform one of three leg-extension training programs three times a week for 10 weeks:

1) One set to failure using a weight that limited them to 8-12 reps

2) Three sets to failure using a weight that limited them to 8-12 reps

3) Three sets to failure using a weight that allowed them to complete 20-30 reps

Immediately after each workout, the subjects ate a protein bar that provided 30 grams of protein, 33 grams of carbs, 11 grams of fat and 4 grams of the BCAA leucine.

They reported in a 2012 issue of the Journal of Applied Physiology that both the subjects training with three sets of 8-12 reps to failure and those training with three sets of 20-30 reps to muscle failure increased leg muscle size by about 7%, which was more than double the increase of those training with just one set of 8-12 reps to failure.

This increase in muscle size was visible in both the slow-twitch and fast-twitch muscle fibers. The take-home point here is that to maximize muscle growth, you definitely need to perform more than one set per exercise, but whether you train in the 8-12-rep range or the 20-30 range doesn't really matter as long as you take each set to muscle failure.

But before you start thinking that it doesn't matter what rep range you choose, the researchers also measured muscle strength and muscle endurance before and after the 10-week program.

They found that the group training with either one set or three sets of 8-12 reps per set increased their one-rep max strength significantly more than the group doing three sets of 20-30 reps. All groups had a similar increase in the number of reps they could complete with 80% of their one-rep max, a weight they could complete for about 10 reps at the start of the program.

But muscle endurance, which they measured by the number of reps they could complete using 30% of their one-rep max, only increased in the group using 3 sets of 20-30 reps.

So although training with both heavy weight and light weight can elicit similar increases in muscle growth, they offer different benefits to the muscle's capacity. The heavier weight leads to better increases in muscle strength, while the lighter weight training induces increases in muscle endurance that the heavy-weight training does not.

Change Up Your Load

The real take-home message from these studies is that you should never stick with one rep range for too long. Regardless of how heavy or how light you go, you will be able to increase muscle growth as long as you train to failure.

Changing up your loads from heavy weight for fewer reps to lighter weight for higher reps also allows you to increase muscle strength and muscle endurance. Having greater strength and greater muscle endurance allows you to train with heavier weights and to complete more reps with a given weight, which can help to better influence muscle growth.

Regardless of what each rep range offers, the simple fact that you're changing things up helps prevent stagnation to allow for continued gains in muscle size, strength and endurance. This is known as the "Weider Muscle Confusion Principle" and it works well -- now we know why!

A great way to change up your rep range is to use linear periodized microcycles, where you start out with lighter weight for higher reps and gradually increase the weight each week until you're down to very heavy weight for low rep counts.

This is similar to my Micro Muscle program. Or try my Up and Down 11-week plan that increases the weight each week, starting with reps way up in the 21-30 range and brings you down to just 3-5 reps per set. You'll then reverse the order, reducing the weight each week until you're back to doing 21-30 reps per set.

You can repeat this indefinitely as long as you change up other variables, such as the exercises used and the rest periods between sets. Just be sure to take each working set to muscle failure or close to it. I can guarantee you'll realize new gains in muscle growth using this type of program.

Up And Down Training

Try this plan that changes up your rep ranges every week. You can use any training split you like and any workouts you prefer. Just keep each set in the prescribed rep range for that week and be sure to take each working set to muscle failure. You can even consider taking the last set of each exercise beyond muscle failure with techniques like forced reps, rest-pause or drop sets.

Week Rep Range
1 21-30
2 16-20
3 12-15
4 9-11
5 6-8
6 3-5
7 6-8
8 9-11
9 12-15
10 16-20
11 21-30


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Fallentin, N., et al. Motor unit recruitment during prolonged isometric contractions. European journal of applied physiology and occupational physiology. 1993;67(4):335-341.

Fuglevand, A. J., et al. Impairment of neuromuscular propagation during human fatiguing contractions at submaximal forces. The Journal of Physiology 1993;460:549-572.

Sale, D. G. Influence of exercise and training on motor unit activation. Exercise and Sport Sciences Reviews. 1987;15:95-151.

Burd, N. A., et al. Low-load high volume resistance exercise stimulates muscle protein synthesis more than high-load low volume resistance exercise in young men. PLoS ONE 5(8): e12033, 2010.

Burd, N. A., et al. Enhanced amino acid sensitivity of myofibrillar protein synthesis persists for up to 24 h after resistance exercise in young men. J Nutr. 2011 Apr 1;141(4):568-73.

Mitchell, C. J., et al. Resistance exercise load does not determine training-mediated hypertrophic gains in young men. J Appl Physiol. in press, 2012.

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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.

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