Expert Nutrition

Muscle Hypertrophy - Understanding Muscle Growth

To properly understand muscle hypertrophy it helps if you first learn some basic human physiology. Hypertrophy basically means cells growing in size, this is different from 'hyperplasia', which means cells growing in number.


Muscles are made up of permanent cells called 'muscle fibers'. As adults we cannot produce new muscles fibers and when their gone –their gone for good. Whilst we can’t produce new muscles cells, we can however change the size of the cells we’ve got. Therefore when you train your muscles and they get bigger, you are not actually growing new muscles cells (hyperplasia), instead each individual muscle cell grows in size (hypertrophy) to help your body cope with increases in muscle loading.

What part of the muscle gets bigger?

A common misconception in the gym is that in order for your muscles to grow you need to tear your muscles such that they grow back stronger. This is incorrect. When you tear a muscle, the muscle cell dies and is replaced with scar tissue, not muscle. Therefore your goal should never be to tear your muscles.

If you look at the diagram below, without getting too technical, basic anatomy shows us that each muscle is made up of muscle fibers (also known as muscle cells). The muscle fibers are then made up of myofibrils and then myofibrils are made up of 2 proteins called actin and myosin (not shown in the diagram).

Muscle anatomy

The size of the muscle fibers in an untrained muscle can vary considerably in diameter. Strength training stimulates the smaller muscle fibers to grow such that they meet the size of the larger ones. This muscle hypertrophy is caused by an increase in the number and size of myofibrils per muscle cell, increased total protein (especially myosin), and increased amounts of connective tissue (tendons and ligaments).

Increases in muscle size (seen in the mirror and measured by tape) can also be a result of increasing capillary (blood vessel) density and through increasing blood flow to the muscle. This increase in capillary density is stimulated by the increased demand for oxygen and blood flow to the muscle during training. This is one of the many ways in which you get fitter, as you train and the demand for oxygen and fuel increases in your muscles your body adapts by increasing capillaries to the region such that next time you can deliver blood more efficiently and better deal with the stimulus.

In summary muscles get bigger as a result of storing more protein within muscle fibers and through increasing the amount of blood vessels and connective tissue. This helps to explain why protein is an important nutrient in your diet when you are trying to build muscle.

Given that when you become an adult muscles cells can't grow in number (hyperplasia), only in size this helps to explain a number of phenomenon.

  1. It helps to explain why if you prescribed a group of people the same exercise program, as a group they will all finish in different shapes and sizes. Some people only seem to look at weights and they bulk up like they have been doing it for years, where as others struggle to get bigger even after years of hard training. Essentially what I’m trying to say is that genetics does play a role in determining how many muscles cells you have. That doesn't mean you can't make what you’ve got, look sexy and hot. More on this later.

    One of the many reasons that some people bulk up more than other is the number of fast twitch muscle fibers they have which is largely genetically determined. Fast twitch muscle fibers are recruited during strength and speed activities and therefore people with a higher percentage of fast twitch muscle fibers will generally find it easy to build muscle size.

  2. What you don't use you lose. When you perform muscle hypertrophy training, muscles generally grow in size to compensate for the need of increased loading, however when you stop training your muscles over time start to shrink. Why? Because as muscles cells get bigger they require more food energy to sustain them (even at rest), therefore when you’re not training enough, they start to shrink back down to help your body become more efficient it the way it burns energy.

  3. The last thing to consider is the effects of aging. Because your body can't grow new muscle cells, this also helps to explain why as you get older you tend to lose muscle mass. After the age of 30, you lose approximately 3% of your muscle mass each decade thereafter. The best way to slow down this process is to remain a regular exerciser throughout your entire life which helps to preserve and maintain the integrity of your muscle cells. As a general rule you don't stop moving because you get old, you get old because you stop moving!

When is the best time to do muscle hypertrophy training?

For athletes muscle hypertrophy training is usually best prescribed early in the off season. There are of course a few variations depending on your chosen field of sport, but for most people this is the ideal time to bulk up as you get good recovery time and other training commitments are limited. This also helps to explain why you will often hear sports commentators say "give him/her another off season." They are usually referring to the hypertrophy training that is prescribed in the off season to help athletes bulk up and build muscle.

Again depending on your chosen field of sport your training focus usually then changes to strength and power in the preseason, and then functional, speed and agility training during competition.

Design your own Muscle Hypertrophy Training Program.

Related Articles to Muscle Hypertrophy


Resistance Training 101

Muscle Building Nutrition Advice

Protein Powder and Gym Supplement Advice

Muscle Building Training Advice

Fit Body Photos and Images

These articles will provide you with the necessary tools to start a successful gym training or bodybuilding program. These principles are only the beginning. Remember that discipline, knowledge and consistency are the keys to achieving your goals. Good luck!

Over the coming months we will be developing this chapter. Please visit our blog and subscribe to our rss feed such that when new articles are added to this chapter you will be notified.

If you have any questions please don't hesitate to contact us for advice.

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