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The Biceps Brachii Function – What Do These Muscles Do?

biceps brachiiAs I continue to study anatomy, I find that I retain information much better if I write it down. So I’m going to start going through the various muscle groups and joints and write down the relevant structures and functions of each. Today it’s the biceps brachii. What is its function? What is it? Where is it?

If you’ve ever flexed your biceps, then you’ve performed a movement with the biceps brachii. It is that big muscle on your arm that Arnold Schwarzenegger is always flexing in his movies. But there’s no need for an Arnold Schwarzenegger workout today in order to learn what’s going on with this ultimate mirror muscle.

What does the biceps brachii do?

Saying that someone “flexed a bicep” isn’t exactly right. To flex something means to put it into flexion. This means to create an angle with the limb that is more acute than 180 degrees, or a straight line. It is actually the elbow that flexes. When the hand is drawn towards the front of the shoulder, that’s flexion. The biceps are not just a muscle for show–they flex the elbow. That is their function.

The other primary task they perform is to supinate the forearm. A hand that is in the supinated position is palm up. I heard a mnemonic once that has helped me remember that: “soup goes in a bowl, make a bowl with your supinated hand.” Silly but effective, in my case.

So that’s it. The biceps rotate the forearm into supinated position and they also help the elbow flex. The opposite of flexion is extension. If you’re wondering what muscles extend the elbow–straighten it back out–you don’t have to look any farther than the other side of the arm: the triceps muscles. But we’ll look at that in the next post.

PS: If you’re looking for a great anatomy primer, especially if you’re into strength training, I highly recommend Frederic Delavier’s Strength Training Anatomy. That link will take you to my review.


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