How Many Reps to Build Muscle?

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The number of reps per set to achieve optimum muscle growth is a fiercely debated and disputed subject amongst the bodybuilding community.

If you go to any popular bodybuilding forum and ask “What’s the best rep range for muscle growth?” you’ll have a variety of different numbers thrown at you, and you’ll end up even more confused than before you asked.

The amount of contradicting opinions on this question is staggering. Everyone seems have their own ‘expert’ opinion on the “perfect” rep range for muscle growth.

But what rep range should you really be training in for maximum gains in muscle?

The truth is, muscle growth can be achieved by training within more than one rep range, there’s no “magic” or “perfect” single rep for muscle growth. However, there is a narrow rep range to work within for optimum muscle growth.

I’ve extensively researched this question and from my experience and study believe that you should be training with the 8 – 12 rep range for maximum gains in muscle growth.

The Science Behind Rep Ranges

Let’s get one thing straight – feeling the “burn” in your muscle from very high rep training does not cause growth. Muscles grow from a combination of tension overload and fatigue. Maximum protein synthesis occurs between 70-85% of your 1RM (one rep max).

A study in 2009 conducted by Kumar et al. (Journal of Applied Physiology) measured the fluctuations in muscle protein synthesis after weight training. They found that the anabolic response (muscle building) increased by:

30% after training with weights that were 20% of 1RM*
40% after training with weights that were 40% of 1RM
100% after training with weights that were 60% of 1RM
130% after training with weights that were 75% of 1RM
100% after training with weights that were 90% of 1RM

(1RM – One repetition maximum, is the maximum amount of weight a person is able to lift for a single repetition*)

As we can see from this information, the peak of muscle growth occurs when training with a weight that is around 75% of our 1RM. The reason that the muscle building response is lower at 90% of 1RM is because the weight is just too heavy. This weight causes the nervous system to fatigue first, not the muscle fibres. This means that the muscles are not receiving enough time under tension to trigger the adaptive growth response.

So how many reps is 75% of your 1 RM? Take a look at the chart below to see how 1RM percentages relate to repetitions:

100% of 1RM = 1 rep
95% of 1RM = 2 reps
93% of 1RM = 3 reps
90% of 1RM = 4 reps
87% of 1RM = 5 reps
85% of 1RM = 6 reps
83% of 1RM = 7 reps
80% of 1RM = 8 reps
77% of 1RM = 9 reps
75% of 1RM = 10 reps
67% of 1RM = 12 reps
65% of 1RM = 15 reps

As you can see, 75% of your one rep max works out at around 10 reps. So, training anywhere between 8 – 12 reps to failure is the optimum rep range for muscle growth.

So why does training in this rep range produce greater gains in muscle size?

Skeletal muscles are made up of a mixture of three different types of muscle fibers. Type 1, Type 2a and Type 2b. The back, legs and neck have a higher number of Type 1 muscle fibers while the shoulders, chest and arms have more Type 2b fibers.

Type 2b fibers come into play when fast of heavy tension is required, such as with heavy weight training around 75% of 1RM. The only way to really stimulate these kinds of fibers is through this heavy weight training. These Type 2b fibers are the most responsive to growth. They will get much bigger and stronger compared to Type 1 muscle fibers.

When you max out/fail between 8 – 12 reps you will recruit ALL muscle fibers, (Type 1, Type 2a and Type 2b) so this is the rep range where you get maximum muscle fiber recruitment which leads to greater increase in size. This rep range gives the best combination of muscle fiber recruitment, metabolic fatigue and good nervous system activation. From the first rep you will get full recruitment and enough time under tension to produce muscle hypertrophy.

Heavy low rep training in the 6 – 8 range does produce great muscle hypertrophy, but slightly higher 8 – 12 reps produces a greater increase in muscle mass.

Ronnie Colman, 8x Mr Olympia, and arguably the greatest bodybuilder of all time said in an interview…

“People always ask me, how do you build muscle? To build muscle you do a lot of repetitions, like 10, 15, that’s how you build muscle!

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