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Lighten Up!

May 21, 2012
Jim Smith Shoulder Light

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 eek out a few reps with very poor form. And you see them training like this with as much weight as possible every time they’re in the gym. Whether they hurt themselves eventually and miss a few months from the gym, or even if they never get the injury they deserve, they will likely not make much progress if they continue to train this way.

But 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 their 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 are barely moving around than getting real results. But since you’re hear on my site, I know that your first priority is getting unreal results. So read on to learn the science on how light weights can help you grow more muscle.

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 reps per set is best for increasing muscle strength; and that the rep range of 7-12 reps per set is best for increasing muscle growth; while reps of 12 and higher are best for increasing muscle endurance. This has always sounded 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 these ways.

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 science often does, there is new research that turns this way of thinking upside down.

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

This is known as the size principle. To keep things simple, there are two main types of muscle fibers – slow-twitch muscle fibers and fast-twitch muscle fibers. Slow-twitch muscle fibers are those with the most endurance and are the smallest and weakest. The fast-twitch muscle fibers are those that have less endurance, but have the most strength and power and grow the biggest.

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

If the weight is too heavy for the few slow-twitch muscle fibers that were recruited, the brain signals the rest of the slow-twitch muscle 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 muscle fibers in the biceps to assist those small, weak and pathetic slow-twitch muscle fibers. If the weight is still to heavy, then the brain calls in the rest of the big and strong fast-twitch muscle fibers to assist and the weight is curled up. Of course this all occurs in a matter of microseconds.

If you were curling the maximum weight that you could lift for one rep, then just about every single muscle fiber from slow to fast would 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 muscle fibers don’t even need to be bothered. Since the fast-twitch muscle fibers are the ones that grow the biggest and strongest and the slow-twitch muscle 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 up 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 muscle fibers with each and every rep completed. And if you take that 20 rep set to absolute muscle failure (the point where you can not complete another rep) then 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 right here 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, then the best way to grow would be to always lift a weight that limits you to one rep. Yet, as we all know, that is 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 is created within the muscle when byproducts accumulate from the biochemical pathways that are used in the muscle cells to produce the energy required to allow the muscles to continue contracting 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 rise higher the higher the levels rise of the metabolic byproduct lactic acid. 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 recruit the same amount of fast-twitch muscle fibers as a heavier set for fewer reps, but you also induce greater metabolic stress. And while all of this sounds good in theory, there is also research that supports this contention. Now does training with lighter weights sound a little more compelling?

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

Their first study that really grabbed the attention of strength scientists, as well as well-read bodybuilders everywhere, was a 2010 study they published in the online science journal, PLoS (Public Library of Science) ONE. They had trained men perform 4 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 who used the 25-rep weight but did not go to full muscle failure. When the men did the 4 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 sets and the 25 rep sets when taken to failure increased muscle protein synthesis far greater than the increase seen in the subjects using the 25-rep weight but not taking sets to muscle failure.

A 2011 study by the same researchers looked at what happens to muscle protein synthesis following heavy-weight 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 one half of those doing the 25 rep sets went to muscle failure on all sets and half did not go to muscle failure. They reported in the Journal of Nutrition that having 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 be noticing right away from 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 is the only way to recruit all of the fast-twitch muscle fibers and instigate enough metabolic stress. These data finally shut up all those strength-training experts who will try to tell that you shouldn’t train to muscle failure at least not on most sets. They claim that it leads to overtraining and it can actually interfere with strength and muscle growth. Of course, the first thing that you’ll notice about most of these so-called experts is the fact that their upper arms barely measure 15 inches. And 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 this “expert” does not 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 overtraining 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 that after sitting on your ass all day at your desk job or in school, that training intensely for 1-1.5 hours is going to cause you to overtrain?! 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.

But hold up there. There are two problems with these two studies. The first is the fact 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 did not measure actual muscle growth over time training these ways. They just looked at a snapshot from one workout. It is a pretty good snap shot, but it still does not 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 per set. Even the most egomaniacal bodybuilder who is more worried about showing off for his fellow gym members rather than actual results, typically does not train in this low 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 University 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 the three leg extension training programs that were performed 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 rep set; or 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 3 sets of 8-12 reps to failure and those training with 3 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 the 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 rep range doesn’t really matter as long as you take each set to muscle failure.

But before you leave 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 that 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.

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 muscle failure. Changing up your weight 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. And regardless of what each rep range offers, the simple fact that you are changing it, keeps the muscle “guessing”, which prevents it from stagnating, and allows for better 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 are down to very heavy weight for few reps.

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 there in the 21-30 range and brings you down to just 3-5 reps per set. Then you reverse the order to reduce the weight each week until you are 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 allowed between sets. Just be sure to take each working set to muscle failure, or close to it and I can guarantee that you will realize new gains in muscle growth.

Up And Down Training

Try this rep range scheme 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 such as 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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