What you’re getting yourself into:
12-24 minute read time
1. Studies across a variety of populations have demonstrated that muscles grow in a very broad variety of rep ranges.
2. When training protocols are matched for number of sets, even with very different training volumes, they generally result in similar levels of muscle growth.
3. Gains in strength and muscular endurance are still very much tied to the rep range used.
4. At least when talking about hypertrophy-based training, it’s more useful to think of “training volume” as “total number of hard sets per muscle” than “sets x reps x load.”
I’m really glad Nathan wrote this article – this is a subject we’ve been chatting about for quite some time now, and this article agrees strongly with my own thoughts on the matter. There are some major drawbacks to the way people usually calculate training volume (sets x reps x weight):
1) Inherently heavier exercises seem necessarily better than lighter ones (i.e. you can accumulate more volume doing leg press than you could squatting, and more squatting than you could front squatting).
2) Training with a lower percentage of your 1rm almost always seems superior to training with a higher percentage (3×10 with a challenging load will mean a lot more volume than 3×3 with a challenging load).
Simply counting hard sets is a much simpler way of accomplishing the same purpose, without unnecessarily biasing some exercises or loading schemes over others. For strength + size, it’s a simple issue of the number of heavy (80-85ish%+) sets you do, for size + muscular endurance, it’s a matter of the number of relatively light (65% and below) sets you do, and for a blend of the two, it’s just about the number of hard sets you do in the intermediate intensity range.
Disclaimer: I’d like to start this article with a disclaimer. What I have written about here are the patterns I have personally seen both in recent strength training literature and in real world strength training. However, I am by no means the most knowledgeable person about physiology or research interpretation, nor am I especially strong or experienced compared to many competitive strength athletes. The patterns I see also seem to be a little bit at odds with what many very smart, very educated people in the strength world seem to see, so it’s possible I am incredibly, horribly wrong about all this. I don’t believe I am, or I wouldn’t be writing this article, but it would be arrogant to not have some doubts. The following is probably best considered as a potentially flawed, but useful model.
For as long as I’ve been lifting, I’ve heard the recommendation that 1-5 reps is for building strength, 8-12 reps is for increasing muscle size, and 15-20 reps is for increasing muscular endurance. Several variations on this theme exist.
The concepts of myofibrillar hypertrophy and sarcoplasmic hypertrophy, usually used to explain strength and size differences between strength athletes and bodybuilders, say that the heavier weights build actual contractile proteins in muscles (myofibrillar hypertrophy), and higher rep ranges (8-12) create more of a focus on increasing sarcoplasm, or the fluid, in muscles. Sarcoplasmic hypertrophy, however, is completely unsupported by any sort of scientific literature (unless Supertraining counts as scientific literature or you count transient increases in fluid as hypertrophy), and strength differences are much more easily explained through other ideas the evidence actually supports.
The American College of Sports Medicine’s recommendations for hypertrophy are that novice trainees perform 8-12RM for 1-3 sets per body part, resting for 1-2 minutes and training 2-3 times/week; whereas, advanced trainees are directed to use 70%-100% of their 1RM for 3-6 sets, with varying rest periods depending on goals, and a 4-6 days/week frequency.(1) Strength training recommendations are similar. However, research over the last few years (and decades of successful methods seen in strength athletes and bodybuilders through time) has demonstrated that while these recommendations likely work, they are only a small part of the total picture.
More recently, Fisher et al wrote a position stand that recommended maximal intensity of effort (lifting to momentary muscular failure) for each set, using a load and frequency that corresponds to the trainee’s goals, and performing a single set per exercise.(2)
Finally, Brad Schoenfeld, my current favorite exercise researcher, published a meta-analysis (a paper that combines the results of multiple studies to find larger patterns in the literature) on the effects of different rep ranges on strength and hypertrophy. The meta analysis compared low loads (<60% 1RM) to high loads (>65% 1RM) and found that there was a greater effect size for hypertrophy in the high loads than the low loads, and that strength improvements were much higher in the high load groups.(3) However, a closer examination of the included studies shows that 6 of the 8 studies examining hypertrophy had the high load groups performing more sets than the low load groups. If you’ve kept up with Strengtheory at all, then you probably know that more sets stimulates more strength and size gains, so this is an obvious confounding variable.
The Size Principle
Before we can dig into the real meat of the subject, it’s important to understand some basic physiology of muscle recruitment. During any set in which you lift a weight to failure, your nervous system will first recruit small/slow motor units and then begin to recruit larger and faster motor units until the force demands are met (or cannot be met).(4) For example (and I’m just making these numbers up to facilitate understanding of the concept), let’s say I can curl a 50 lb. dumbbell 10 times. During the first 3 reps, I might only be using small/slow motor units and muscle fibers. By the 6th rep, the smaller fibers have fatigued a little and can no longer produce enough force to move the weight, and I begin recruiting larger muscle fibers. By the 10th rep, all the muscle fibers in my biceps have been recruited and have experienced enough fatigue that they can no longer produce enough force to move the weight, and I fail the 11th rep. The size principle is more complex than this in actual practice, but this explains the basic concept.
Now, what happens if instead of a 50 lb. dumbbell, I pick up a 25 lb. dumbbell and lift to failure at 20 reps? The exact same pattern repeats. The same basic thing also happens if I pick up a 75 lb. dumbbell and lift to failure at 3 reps. As far as the muscle knows, the same thing has happened each time: All the muscle fibers were recruited and eventually something happened to make them less able to produce force.
Now, there is some recent EMG evidence that calls into doubt whether the biggest/fastest motor units are recruited during high rep sets to failure in trained lifters, but there are several possible explanations for the lower EMG readings with low loads,(5) and the size principle has thus far stood the test of time. It could be that while the largest fibers were indeed recruited during low load lifting to failure, less fibers were being recruited simultaneously, so the peak EMG was lower. It could also be that trained lifters who have been lifting in a certain rep range for a long time are able to put forth more effort in that rep range (typically a heavier load), and if they had trained for a few weeks with the lighter load, they would have learned to put forth equivalent effort.
What causes the muscles to fatigue?
Fatigue during resistance training is still a very slippery concept. However, we do know that when a muscle contracts, metabolic byproducts are created. In addition, during a contraction or any time a muscle is under tension, blood flow to and from the muscle is restricted, and the metabolites are cleared more slowly. When the metabolite production is greater than the cardiovascular system’s ability to remove them, the concentration increases and begins to interfere with muscle contraction. It is also likely that they stimulate the sensation of pain, and your brain might take that pain and decide to put less effort into motor unit recruitment. Whatever is happening is almost certainly a combination of effects at the muscle and the central nervous system.
This concept is probably best exemplified by a technique called blood flow restriction training. In it, a tourniquet is applied to a limb in order to reduce blood flow for the duration of a set. Significantly less weight and fewer reps can be done with this method, but it has been shown to produce the same muscle growth as heavier weights without blood flow restriction.(6)
So why is this concept important? Because, at least at this point, it seems as if muscle fibers must be recruited and experience at least some fatigue in order to grow larger. Something about the fatiguing process signals hypertrophy to begin. I like to envision each instance of fatigue as stimulating a small amount of hypertrophy, so multiple instances of fatigue – multiple sets to failure – builds up a large amount of hypertrophy stimulation.
Effect of Different Rep Ranges on Hypertrophy
Now that we have an understanding of some general background information, we can examine the effects of different rep ranges on muscle growth.
First, we need to find studies that control for the effort per set so that we don’t have a group doing sets only halfway to failure (and thus not recruiting and fatiguing all available fibers) versus a group doing sets all the way to failure.
Next, we need studies that control for training volume (weight x reps) or number of sets. If one study has a group do a single set to failure and another group doing 10 sets to failure, we won’t be able to tell if differences in strength and hypertrophy are due to the rep ranges used or due to the difference in number of sets.
Luckily, we have a decent number of studies available that have done what we need. I’ve summarized the results in the following table. All sets in all of these studies were performed to failure.
Digging into these studies, several patterns appear. In the Campos study, the light loads did not produce as much (if any) hypertrophy as the heavier loads. However, the light load group also did fewer sets than the groups with heavier loads in an attempt to match volume-load. Assuming the loads don’t make a difference (possibly a dangerous assumption, but safer when the whole body of literature is considered), this seems to indicate that number of sets might be what determines hypertrophy. However, in the Schoenfeld 2014 study, one group did exercises for 3 sets of ~10 reps and the other group did exercises for 7 sets of ~3 reps (again, matching volume-load). If number of sets is what matters, the 7×3 group should have had more hypertrophy, but they didn’t. Digging deeper, though, the lighter load group actually did 9 sets to failure per week per body part, and the heavier group did 21 sets to failure per body part per week. When the total number of sets that stimulated each muscle are taken into account, it seems possible that 9 sets to failure per week or less may have stimulated the maximum amount of hypertrophy in this specific training population, and the additional 18 sets per week done by the heavier group contributed little if anything to extra hypertrophy.
The Van Roie study also used volume-load rather than number of sets, but saw no differences in hypertrophy.
The rest of the studies generally matched the number of sets between groups, and they help to fill out the pattern: Different rep ranges seem to have the exact same effect on hypertrophy. Not only that, but these studies represent untrained, well trained, and even elderly populations, so the similarities in hypertrophy hold true wherever we look.
The next pattern that appears is that heavier weights make the participants better at lifting heavier weights, and lighter weights make the participants better at lifting lighter weights, even though muscle growth is the same. This could be due to a variety of factors that as of yet are unexplored in the literature: neural adaptations to specific loads, fiber type specific hypertrophy, aerobic/anaerobic adaptations in muscle fibers, and so on. I personally lean toward the effect being mostly neural in nature, with actual differences in muscle adaptation being minimal, but that’s abject speculation on my part and it remains to be seen what the real answer is. I’ll believe that lighter loads preferentially stimulate type I fiber hypertrophy when I see actual measurements of individual fibers like in the Campos study. There are a couple of studies looking at muscle fiber types in drug-free competitive weightlifters(15) and powerlifters,(16) and the fiber type ratios are very similar. A few more studies have looked at bodybuilder fiber types and found a very high ratio of type I fibers,(17,18) but they were done on high-level, untested competitors and had exceedingly small sample sizes, so the likely drug use and other factors such as different muscle groups in the different studies make it difficult to draw conclusions. In addition, none of the studies examining fiber types are training studies, so the actual effect of certain rep ranges on the fiber types would be impossible to know anyway.
The third pattern that emerges, at least to me (and this is mostly based off studies not included in the table) is that a higher number of sets increases the effects on strength and hypertrophy.(19) In the Campos study, for example, the two heavier groups did more sets than the lighter group because they attempted to control for volume-load, and there was no hypertrophy seen in the lighter group. However, in several of the other studies, we can see that the lighter loads do actually stimulate hypertrophy when more sets are done.
So what does this all mean? I believe there are several main principles that can be derived from these patterns.
- From the size principle, we know that sets must be high effort to recruit and fatigue all fibers. We don’t know the exact threshold for the effort needed to stimulate hypertrophy, and there are plenty of people who experience considerable muscle growth never lifting to failure, but generally it’s probably necessary to push sets within a few reps of failure.
- Rep range does not matter for hypertrophy (at least up to 30 reps/set for trained lifters and 100 reps/set for untrained old people), so long as the effort per set is equal. Muscles seem to grow the same whether you lift 3 reps to failure or 100 reps to failure. It remains to be seen whether muscles grow the same with something like 70% effort matched between groups rather than lifting to failure, but I believe they would.
- Strength increases are highly specific to the rep ranges used. If you want to get better at one-rep max attempts, you need to lift loads that are close to that. If you want to get better at high reps, you need to lift lighter loads. You can likely get better at both by doing both rep ranges. Think of the strength increases as studying specific material for an exam.
- Doing more sets or volume (it’s still a little unclear which better predicts gains, although I lean toward more sets) gives you more results.
With this information, it’s easy to answer a question from earlier in this article: Why is there a strength and size difference between strength athletes and bodybuilders? The answer to the strength difference lies in the rep ranges used. Strength athletes generally include heavier rep ranges, and many bodybuilders stay in a less injury-prone rep range. However, many bodybuilders compete successfully in powerlifting by adding in heavier work.
The size difference is a little trickier; I do not actually believe there is a muscle size difference between bodybuilders and strength athletes at similar levels. The difference is an illusion caused by different levels of body fat and a focus on muscles that primarily enhance aesthetics versus muscles that enhance strength. Muscles that both groups work hard, such as legs, back, and chest (I’m generalizing in order to get the concept across) should be similar in size.
To put it more simply, strength training is bodybuilding, and bodybuilding is strength training for whatever rep range you are using.
Holes In This Boat
There are a few concepts that the literature has yet to examine satisfactorily. The first, as mentioned earlier, is what causes the strength adaptations to specific rep ranges. Do type I fibers get stimulated more with high rep ranges? Do more aerobic adaptations occur with higher rep ranges? Is the difference entirely due to neural adaptations and motor learning? We just don’t know yet.
The second is the degree of effort necessary per set to maximally stimulate hypertrophy; do we actually need to lift to failure, can we stop short of failure, or can even very low-effort sets stimulate some hypertrophy? In the real world, it looks as if even very low effort can cause some muscle growth, but the matter is yet unresolved. In addition, adding more lower effort sets might decrease any differences.
Finally, and this is likely the biggest and most important question, but what exactly stimulates hypertrophy? There are hypotheses out there, some of which are supported by evidence, but in my opinion, it is still inconclusive.(20) Tension on muscles themselves might be enough to stimulate hypertrophy, but when you get tension, you also get ischemia and increased metabolite build-up. The pump you get from lifting weights might contribute, but heavy weight/low rep sets tend not to elicit much of a pump, and hypertrophy has been shown to be the same as for higher rep sets. Metabolic byproduct concentration might be the main stimulator, but there isn’t much evidence examining the idea yet. At this point, we can only conclusively look at muscle growth on a large scale and say that picking things up and putting them down a lot makes muscles get bigger.
Upon examining the history of strength and physique sports, a nearly infinite number of strategies can be seen to have been successful. However, the most successful strategies appear to follow a few basic rules very similar to the takeaway principles mentioned earlier. Keep effort high, keep number of sets high, and tailor your rep ranges to your goals or whatever keeps you motivated, and progress shouldn’t be a problem.
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- American College of Sports Medicine. Progression models in resistance training for healthy adults. Med Sci Sports Exerc. 2009;41(3):687-708.
- Fisher J, Steele J, Smith D. Evidence-based resistance training recommendations for muscular hypertrophy. Med Sport. 2013;17(4):217-235.
- Schoenfeld BJ, Wilson JM, Lowery RP, Krieger JW. Muscular adaptations in low- versus high-load resistance training: A meta-analysis. Eur J Sport Sci. 2014;:1-10.
- Carpinelli, RN. The size principle and a critical analysis of the unsubstantiated heavier-is-better recommendation for resistance training. J Exerc Sci Fit. 2008;6(2)67-86.
- Schoenfeld BJ, Contreras B, Willardson JM, Fontana F, Tiryaki-sonmez G. Muscle activation during low- versus high-load resistance training in well-trained men. Eur J Appl Physiol. 2014;114(12):2491-7
- Loenneke JP, Wilson JM, Marín PJ, Zourdos MC, Bemben MG. Low intensity blood flow restriction training: a meta-analysis. Eur J Appl Physiol. 2012;112(5):1849-59.
- Weiss, LW, Coney HD, Clark FC. Gross measures of exercise-induced muscular hypertrophy. J Orthop Sports Phys Ther. 2000;30(3):143-148.
- Weiss LW, Coney HD, Clark FC. Differential functional adaptations to short-term low-, moderate-, and high-repetition weight training. J Strength Cond Res. 1999;13(3):236-241.
- Campos GE, Luecke TJ, Wendeln HK, Toma K, Hagerman FC, Murray TF, Ragg KE, Ratamess NA, Kraemer WJ, Staron RS. Muscular adaptations in response to three different resistance-training regimens: specificity of repetition maximum training zones. Eur J Appl Physiol. 2002;88:50-60.
- Alcaraz PE, Gomze PJ, Chavarrias M, Blazevich AJ. Similarity in adaptations to high-resistance circuit vs. traditional strength training in resistance-trained men. J Strength Cond Res. 2011;25(9):2519-27.
- Mitchell CJ, Churchward-Venne TA, West DW, Burd NA, Breen L, Baker SK, Phillips SM. Resistance exercise load does not determine training-mediated hypertrophic gains in young men. J Appl Physiol. 2012;113:71-77.
- Schoenfeld BJ, Ratamess NA, Peterson MD, Contreras B, Sonmez GT, Alvar BA. Effects of different volume-equated resistance training loading strategies on muscular adaptations in well-trained men. J Strength Cond Res. 2014;28(10):2909-18.
- Van Roie E, Delecluse C, Coudyzer W, Boonen S, Bautmans I. Strength training at high versus low external resistance in older adults: effects on muscle volume, muscle strength, and force-velocity characteristics. Exp Gerontol. 2013;48(11):1351-61.
- Schoenfeld BJ, Peterson MD, Ogborn D, Contreras B, Sonmez GT. Effects of Low- Versus High-Load Resistance Training on Muscle Strength and Hypertrophy in Well-Trained Men. J Strength Cond Res. 2015.
- Fry AC, Schilling BK, Staron RS, Hagerman FC, Hikida RS, Thrush JT. Muscle fiber characteristics and performance correlates of male Olympic-style weightlifters. J Strength Cond Res. 2003;17(4):746-54.
- Fry AC, Webber JM, Weiss LW, Harber MP, Vaczi M, Pattison NA. Muscle fiber characteristics of competitive power lifters. J Strength Cond Res. 2003;17(2):402-10.
- Macdougall JD, Sale DG, Elder GC, Sutton JR. Muscle ultrastructural characteristics of elite powerlifters and bodybuilders. Eur J Appl Physiol Occup Physiol. 1982;48(1):117-26.
- Tesch PA, Larsson L. Muscle hypertrophy in bodybuilders. Eur J Appl Physiol Occup Physiol. 1982;49(3):301-6.
- Krieger JW. Single vs. multiple sets of resistance exercise for muscle hypertrophy: a meta-analysis. J Strength Cond Res. 2010;24(4):1150-9.
- Schoenfeld BJ. The mechanisms of muscle hypertrophy and their application to resistance training. J Strength Cond Res. 2010;24(10):2857-72.