Why and How Do Muscles Get Bigger When Exercised?

We all know that we’re supposed to work out if we want our muscles to get better, and we’re all familiar with the kind of thing that entails – usually curling or pressing a heavy weight several times under strain until it starts to really ache. But what is the purpose between this seemingly arbitrary and certainly repetitive behaviour? How does repeatedly moving a heavy object translate to growing huge guns?

Understanding a process can in the vast majority of cases help us to improve our performance in it, and this is no different with weightlifting and hypertrophy (the technical term for when our muscles get bigger). Here we will look at what’s actually going on under the hood and how to make sure it keeps happening.


When you lift a heavy weight this means you strain with your muscle to move it and that in turn places a lot of stress on your muscle fibres (the tiny bits that make up your biceps). What this then does is to cause a tiny little tear in the fibre as it starts to fray – like pulling an elastic band as hard as you can for a while it will of course inevitably start to come apart. This is what causes the pain in your muscles that you might refer to as the burn – of course ripping any part of your body is going to hurt.

Amino Acids

But fret not, as actually in this case you want your muscle to tear and the reason for this is that it’s going to trigger the growth you want. When your muscles are torn this holds up a red flag to your body and tells it the area needs repairing. Then you eat protein – amino acids – and this gets rushed to the site where the damage has been done in order to rebuild it and heal the muscle. This is possible because amino acids are both what protein is made of and what the tissue in your body is made of, so basically you’re recycling that chicken or pork to build up your body.

The reason that this is a good thing, is that in repairing your muscle fibres your body is actually also making them bigger and stronger. Just as scar tissue is actually stronger than regular skin and flesh, so does healing our microtears cause those muscles to come back thicker and stronger. You can’t increase the number of muscle fibres, but by continually making them thicker en-masse you are able to build them up bigger and stronger.

Note of course that in order for this to happen you need to first train to the point where the muscles are tearing, but also ensure that your body has the necessary amount of amino acids available to make the necessary repairs.


Your body effectively has two different ‘modes’ and these are ‘catabolic’ meaning it burns fat and provides you with energy, and ‘anabolic’ meaning that it’s resting and using fat and protein in order to heal tissue (including muscles).

In other words the repairs in your muscles will only occur if you have the required amino acids and you are in an anabolic state. These anabolic states meanwhile are triggered by the production of hormones such as testosterone and in particularly growth hormone. The good news is that the body will automatically enter an anabolic state immediately after exercise – which is why this is the time that most bodybuilders and athletes will use protein shakes. However you are also in an anabolic state during sleep, and when you artificially stimulate the pituitary glands to produce more growth hormones through the use of supplements or even just by taking a hot shower.

This is also why rest is so important if you want to achieve maximum muscle growth – you need to not only put in the training but also then get the necessary rest and protein in order to allow the muscles to recover and come back larger and stronger than before.

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Adam Sinicki

Adam Sinicki is a full time writer who spends most of his time in the coffee shops of London. Adam has a BSc in psychology and is an amateur bodybuilder with a couple of competition wins to his name. His other interests are self improvement, general health, transhumanism and brain training. As well as writing for websites and magazines, he also runs his own sites and has published several books and apps on these topics.

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