Bodybuilding Muscle Anatomy Explained

Bodybuilding Muscle Anatomy Explained

Show us your guns? You don’t have to actually; we can’t see you. But if you did just move up your arm and flex your bicep, then your body has gone through a structured process to achieve this motion. In fact, right now your eyes are using muscles to read this. Anyway, tense your bicep…

You just fired messages from your eyes to your brain, and down your spine through your CNS to your PNS, firing up motor neurons which control motor units, releasing ATP and shortening and lengthening sarcomeres (sections of muscle fibres) caused by of a nodding motion in actin which pulls itself over the thicker myofibril in the middle of your muscle cells myofilaments (individual fibre of muscle).  This is the rough process of tensing your little bicep.

So, what does all that mean?

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Muscles 101

So, you have over 600+ (the exact number is disputed) muscles in your body. Your muscles are divided into 3 key types, smooth, cardiac and skeletal, you can read more about that here.

Skeletal muscle is what allows you to lift weights (and so does cardiac in a sense) and is what you want to grow through a process called hypertrophy. Your skeletal muscle is attached to your…we don’t need to explain that.

It is attached to your bones via your tendons, and only moves voluntarily when you consciously want it to. This stimulus comes in the form of an electronic signal. Normally from your brain, however a tazer or other external electronic stimulus can also cause muscle tissue to contract.

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What is Muscle? 

Muscle is made up of muscle cells, or myocyte.

Remember told you to tense your bicep, what you need to picture when you do that is your bicep is layered. Imagine a thick cable, with smaller and smaller cables inside it. First you have the tendon, which is the connective tissue between the bone and the muscle.


Your whole muscle is surrounded with a dense piece of connective tissue called the epimysium. This is essentially what you’d call the glue which keeps your muscle tissue grouped together.

If you were to split away a grouping of tissue from within this, you’ll find your fasciculi (groups of individual muscle fibre), which are held together by the perimysium (connective tissue). If we pull out the fasciculi, we’d find the single muscle fibres grouped together within it. The connective tissue around these groupings is called endomysium.

Then (yeah, sorry there’s more), if we pulled out a single muscle fibre, we’d find it made up of a group of myofibrils. And these are where the magic happens.

Your myofibrils are like ropes, made up of segments called sarcomeres which connect to one another down the myofibril with a sort of devils teeth zig zag at every connection. These tiny sarcomeres are where contraction and relaxation takes place.

Now, here’s that in reverse. Tensing your bicep, causes your sarcomeres to shorten, which shortens each individual muscle fibre in that group. This then works up through all the bundles of fibres which get bigger and bigger until that particular muscle is tense.

Sarcomeres and the Sliding Filament Theory

So let’s strip back to the myofibril and it’s string of sarcomeres, in order to contract and move the muscle, the theory, and we stress theory here as there’s still some debate surrounding muscle anatomy, is that the with the contraction of a muscle, each sarcomeres myofilaments, or working parts, made up of actin and myosin, move. The actin, which is a thin filament on both sides of a thicker middle filament (myosin) will make a backwards wave motion over the thicker middle filament, pulling itself together over each side.

Imagine two dogs eating the same sausage. The myosin is the sausage, and the tops and bottom jaws of the dogs are the actin. As they eat the sausage, they move down it in a sort of chomping or nodding motion. This is what myofilaments do when your muscle contracts. Obviously, if you relax your muscles, then the dogs are going the opposite way. Weird comparison, if you’ve got a better one comment below.

This is all the theory anyway. 


How Do Your Muscles Move?

When you tense your bicep then, what triggers this movement? And how is it controlled?

It all starts with sensory neurons; these are inside your muscle. They send a message telling your brain the location of the muscle essentially, through your peripheral nervous system to your central nervous system and up spine. This goes up to your brain. Where your brain then fires the electrical signal back down, through the CND to the motor neurons. Your motor neurons then send impulses to the motor units, controllers of muscle fibres and your sarcomeres will contract. And again, your bicep is tense.

One key part of this is that as you train, you’ll develop more connections and eventually be able to recruit more motor units. Which makes you stronger and more efficient. If you’re inactive for long periods, then this whole process will slow down.

You can improve these connections with supplements, but generally training them is what works best.  As you grow older, you’ll experience a natural decline in these connections and also in other areas of growth. This is natural. But regular training can offset this, and it’s entirely possible to continue growth as long as you are training correctly.

Training is vital as you get older to slow this decline.

Bodybuilding Muscles Conclusion

We hoped we helped with your understanding a little. As with anything, the world of muscle physiology and theory is constantly evolving. But here’s the answer what your muscles are made from, what’s inside your muscles and how your muscles move.

In order to maintain muscle and performance, it’s vital that you pick the right program for your goals. You can check out all our training articles here.