The science behind building muscle

Muscle building is a worthy endeavour. Not only do well-built and defined muscles look great, they’ll also help you be more functional and protect your health.

Large muscles are (usually) strong muscles, and strong muscles are highly functional. They help you run faster, jump higher, lift and carry heavier things, and manipulate your own bodyweight with greater ease. Ultimately, larger and stronger muscles help you navigate through daily life more freely.

Developing muscular size and strength also makes you healthier and less likely to lose your life. Research in medical science has consistently shown that greater muscular strength is strongly linked to a reduced likelihood of dying by any means (known as ‘all-cause mortality’). For example, a study in the journal, Archives of Physical Medicine and Rehabilitation looked at data from around 1.9 million men and women and found that higher levels of muscular strength in either the upper- or lower-body is associated with lower risk of all-cause mortality, even in seniors and older adults.

As you can see, building large, strong muscles is highly beneficial. But, what types of exercise are effective if muscle building is your goal?

Types of exercise that build muscle

Any exercise that forces your muscles to contract against an external resistance (i.e., some kind of weight) will stimulate muscle growth (known as hypertrophy). Deliberate and consistent exercise of this kind is called resistance training or resistance exercise.

The most common and effective types of resistance training intended to build muscle are weight lifting and bodyweight training (also known as calisthenics). Weight lifting includes the use of free weights like dumbbells and barbells, as well as machines (such as a leg press machine or home gym). In basically all forms of resistance training, workouts consist of specific exercises completed as a number of repetitions (‘reps’ for short) and sets with a given weight.

It’s a widely held belief that resistance training with free weights is more effective for building muscle than training with machines or doing calisthenics. This belief has been around for decades, and even made it into the American College of Sports Medicine (ACSM) Position Stand on Progression Models in Resistance Training for Healthy Adults.

The problem, however, is that scientific research on the topic strongly disagrees with this claim. Studies comparing free weights and weight lifting machines have regularly found neither to be superior for simulating hypertrophy (see this study and this study as examples). This is great news because it means your options for building muscle are not limited. You can and should choose the method that you’re most comfortable with, and to which you have the easiest access.

So, if the method for building muscle doesn’t really matter, what does? Let’s take a look.

Principles of muscle-building

Increasing the size and strength of your muscles isn’t rocket science, but it is a science. There are a number of scientifically validated principles behind building muscle that can help you choose or design an exercise program that will help you be as successful as possible at packing on size.

1. Intensity and Number of Reps

The term ‘intensity’ is not used consistently in the context of resistance training. Sometimes it’s used to refer to effort and at other times it’s used to refer to load.

Load simply refers to the amount of weight being lifted, and is usually expressed as a percentage of 1 repetition maximum (1RM; the maximum weight with which a single repetition can be completed with proper technique). For example, if your 1RM for biceps curls is 75 lbs, and you do a set of biceps curls with a 45 lbs weight, then the intensity (or load) is 70% of 1RM. This is obviously closely related to the number of reps you can do. When lifting heavy loads, you’ll only be able to do a small number of repetitions (1 – 6 reps)

Another widely held belief in the resistance training community is that different loads produce different changes in the muscles. High loads (85% of 1RM or more) are said to produce the greatest increases in strength. Low loads (Less than 65% of 1RM) are often said to lead to the greatest increases in muscular endurance. Finally, medium loads (between 65% and 85% of 1RM) are thought to be most effective for building muscle. Again, this is not supported by the research.

The vast majority of studies looking at different loads for building muscle have found little or no difference between high, medium and low loads. That is, it almost certainly doesn’t matter if you lift very heavy weights, moderately heavy weights, or relatively lighter weights. All can be equally effective for stimulating muscle hypertrophy. What does matter for muscle building is the effort you put in.

Effort can be thought of as the number of reps completed with a given weight compared to the number of reps possible. So, if you do a set of 8 biceps curls with a 45 lbs weight, but you’re actually capable of doing 10 reps, then the intensity (or effort) is said to be 80%. You must work close to 100% effort,in order to stimulate muscle growth. An easy way of judging your effort is by examining the extent to which you’re completing sets of exercises to momentary muscular failure (MMF) – the point at which another repetition with proper technique would be extremely difficult or impossible. Studies on muscular hypertrophy have indeed shown that working to MMF or within 2 reps is necessary to effectively build muscle.

In summary, it’s not necessary to lift heavy weights to build muscle effectively. If you want to do a small number of reps with heavy weight then go for it. If you’d rather use lighter weights and do more reps, then that’s fine too. Irrespective of the number of reps you do, it is necessary to work close to 100% effort. As far as possible, work to momentary muscular failure. That is, whatever number of reps you do, always ensure that the last rep of each set you complete is extremely difficult or impossible.

2. Volume

Volume refers to the total amount of work you do when resistance training. It’s calculated by multiplying the load x reps x sets. For example, if you do 3 sets of 10 reps of biceps curls with a 50 lbs weight, then the volume will be:

3 x 10 x 50 lbs

= 1500 lbs

Conventional wisdom has long been ‘more is better’; higher volume resistance training programs result in greater gains in muscle size than lower volume programs. It’s important to note here that volume is typically adjusted by altering the number of sets you complete of exercises for specific muscles / muscle groups in a given time period (usually over a week). That means more sets = higher volume.

Unfortunately, the science is not exactly clear-cut on this issue. There is a good deal of evidence to suggest that more is not better, and that low-volume resistance training can be just as effective for muscle hypertrophy as high-volume training. Conversely, a meta-analysis published in the Journal of Sports Sciences found that there is a dose-response relationship between training volume and muscle hypertrophy, which is a fancy way of saying more volume = more muscle. That study suggested that optimal muscle growth happens when you train each muscle group with 10 or more sets per week.

A closer examination of the research on volume suggests that higher volume training is more effective than lower volume training, but only when using very high volumes (i.e., more than 10 sets per muscle group per week). There’s unlikely to be much difference in muscle growth between low volume training (e.g., less than 4 sets per muscle group per week) and moderate-to-high volume training (between 4 – 9 sets per muscle group per week).

In summary, the research suggests that you can effectively build muscle without having to do heaps of sets, and train for hours and hours. In fact, you should be able to make significant gains in muscle size with only a few sets per week per muscle group. As long as you’re putting in that close to 100% effort, your muscles will get bigger.

3. Protein

Proteins are the building blocks of muscles, so your muscles need protein in order to grow. And that means you need to be getting sufficient amounts of protein in your diet. The sport and exercise science research is agreed on this. The question that is often studied is “how much protein is needed to ensure muscle growth?”

Well, research has a pretty straightforward answer to that. A meta-analysis in the British Journal of Sports Medicine found that ingesting approximately 0.72 grams of protein per pound of bodyweight per day will produce optimal muscle growth.

That means, if you weigh 150 lbs, to maximize muscle growth you need to eat:

0.72 x 150

=  108 grams of protein per day

This number is an average, meaning you want to be ingesting this much protein, on average, for as long as you’re doing resistance training.

To give you an idea of how much protein is in various kinds of food, an average sized egg contains about 13 g of protein, chicken breast contains about 32 g of protein per 100 g of breast, and an 8 ounce glass of full-cream milk contains about 8 g of protein. Because many people can struggle to eat the optimal amount of protein needed for muscle growth, using a protein supplement is a common strategy to help build muscle. Using a good quality protein supplement is perfectly acceptable – just make sure it’s whey protein, and not soy protein.

In summary, you’ve got to eat enough protein if you want to effectively build muscle, because proteins are the building block of your muscles. If you want to optimize your muscle building, then you want to eat an average of about 0.72 grams of protein per pound of bodyweight per day. If you’re unable to ingest that much protein via regular food, it’s perfectly fine to use a good whey protein supplement.


One of the main barriers to taking up muscle building exercise is the perception, or misperception, that it’s difficult and complex. The resistance training community is filled with misunderstandings, half-truths, and conventional wisdom that isn’t particularly wise.

Research in the area of sport and exercise science has shown that, contrary to popular belief, all forms of resistance training are equally effective in building muscle. Free weights are not superior to machines or bodyweight training. If you are more comfortable with and / or have easier access to cable weights machines, then go ahead and use them knowing that you won’t be compromising the effectiveness of your workouts. What you workout with is less important than how you workout, but even this is less complex than many would have us believe.

Research has produced a lot of evidence to suggest that it’s not better or worse to train with heavy weights or light weights, or do few reps or many reps. What matters more, is that you’re training near 100% effort, and that you’re completing each set of an exercise to momentary muscular failure.

Similarly, the volume or number of sets doesn’t seem to have a huge impact on muscle hypertrophy, except at very extreme levels. You don’t have to do copious amounts of sets each week in order to effectively put on muscle. Even doing a few sets of an exercise per muscle group per week can lead to substantial gains.

Finally, it’s important to feed your muscles with enough protein to ensure they have the building blocks for growth. As long as you’re doing resistance exercise, you should be aiming to get approximately 0.72 grams of protein per pound of bodyweight per day.

Follow these simple, science-based recommendations and you will be impressed with the consistent and significant muscle growth you can achieve.