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How many reps to build muscle?

By Dr Peter Griffiths

Take a look on any bodybuilding forum or discussion site and you will see that one of the most frequently asked questions, especially among beginners, is “How many reps is best to build muscle?”

It’s not surprising that this is one of the major questions for two reasons:

First of all, people want results. If you’re anything like me you don’t want to waste time in the gym. When I train I want to know that the effort I’m putting in will build me the most muscle in the shortest time possible.

Secondly, if you take a look around on the internet you’ll see that there has been a lot of discussion on this point. There seem to be a lot of contradictory opinions floating around. A lot of these opinions are based on the “this is what has been found to work” or “this is what person X does” variety.
Of course the experiences of successful bodybuilders cannot be discounted when it comes to muscle growth, but why isn’t there any kind of definitive answer based on science?

Well, actually a lot of studies HAVE been done on precisely this question of “how many reps”. Unfortunately for us many of them suffer from drawbacks in their design which makes their conclusions unreliable or not applicable to the average gym goer.

Let’s look at some of them to see what conclusions we can draw, but first of all let’s define some terms. For the purpose of our discussion we’ll call low reps to be reps in the 1-5 range as typically used by power lifters for strength training. Mid reps are in the 6-12 range as traditionally used by bodybuilders. Anything above 12 reps we’ll call high reps.

Also before we begin let us discount the “hormone hypothesis”. This is based on the fact that some studies have shown that mid reps with short rest periods increases the short term GH and testosterone peak after exercise more than higher weight, low reps. However it has now been shown that transient hormone changes induced by exercise do not aid muscle growth. See my other article “doing 20 rep squats to increase testosterone is pointless” for more discussion of this.

So what have other studies shown? One interesting study (1) looked directly at muscle protein synthesis following weight training using different rep ranges (since muscle growth depends on protein synthesis this should directly measure the effectiveness of each rep range at stimulating muscle growth). The results can be seen in the figure below.

fig 1

As we can see high rep ranges corresponding to 15%-45% of the 1RM (using 15%-45% of the 1 repetition maximum weight) which in this study was 27-14 reps produced considerably lower protein synthesis. What is surprising though is that although maximum protein synthesis occurred at 75% 1RM which was 8 reps, statistically this was not significantly different from the protein synthesis induced by 90% 1RM which was 3 reps (the 60% 1RM corresponded to 9 reps). The figures given in the chart for older men are slightly different but these were all men over 75 so we won’t go into them here.

So the mid rep range produced the greatest protein synthesis, but it wasn’t different enough from the low rep range to say for certain the results actually mean anything. Are there any other studies which show the same thing? Yes there are a couple of other studies, one measured muscle fibre growth by taking muscle biopsies (2) and the other measured total muscle cross sectional area by MRI scan. They both came to the same conclusion, that there is no significant difference between low reps and mid reps for inducing muscle growth (although all studies agree that high reps are the least effective).

The problem with all these studies though is they suffer from one big problem – they all used untrained subjects. And as we all know beginners will gain muscle on virtually any kind of training program - something which has also been confirmed by many studies.

What we need are studies which look at people on a long term basis which corresponds more to the real life scenario of someone training regularly for several years.

Fortunately we do have one such study which is actually quite old which might explain why it is not better known. In this study the researcher followed a group of elite Olympic powerlifters using a typical low rep protocol for a period of two years. At intervals he took measurements of muscle fibre cross section, strength, weight lifting results and serum hormones. After two years despite improvements in strength and weight lifting results the lifters showed very little increase in muscle fibre hypertrophy as shown in the diagram below.

fig 2

Of course, this study can also be criticised on the grounds that elite Olympic lifters also bear as little relationship to the average regular gym goer as a complete beginner in the previous studies.

But in conclusion what can we draw from all this?

Firstly – over the long term one study shows that a typical low rep power lifting routine did not lead to significant muscle growth in experienced lifters, although strength did increase.

Secondly - the first study we looked at showed that at least in beginners maximum growth occurs at around 75% 1RM firmly in the mid rep range. Although this result wasn’t statistically significant it does at least show that mid reps are definitely at least equivalent to low reps.

Finally if we add to all this the real life experience of bodybuilders most of whom have been using mid rep ranges since bodybuilding split from powerlifting in the 1940’s because they were convinced it was more effective then you have a powerful argument to say that if you want to stimulate muscle growth then the answer to the question "how many reps to build muscle?" is you should train using 6-12 reps.

how many reps to build muscle