I've blogged recently a little about the bicep muscle, but time now for a little more detail.
Muscles pull on bones to cause movement. The main movement that the bicep causes is pretty obvious: it bends the arm at the elbow; this movement is called flexion.
The muscle's actual name is biceps brachii:
So biceps brachii is the 2 headed muscle of the arm.
The "2 heads" of the biceps muscle refers to the fact that there are actually 2 bellies of the muscle, each starting (originating) in slightly different places. These 2 heads are pretty much merged into a single muscle belly.
There's a long head and a short head of biceps.
If you stand with your arm hanging down by your side, with your palm facing forwards, short head of biceps is closest to your torso, and long head on the "outside"
If you connected a stretched spring to the lower arm and the upper arm, then allowed the spring to contract, it's fairly easy to visualise what would happen - the arm would bend at the elbow (flex).
That's pretty much what happens with the biceps, except there are a couple of refinements:
Both heads of the bicep in fact have tendons that go all the way up the arm, over the point where the arm bone sits in the shoulder socket, and those tendons attach to slightly separate places on the shoulder.
What that means is that as well as flexing the arm (bending it at the elbow), the biceps also have a lever effect on the arms as whole from your shoulder... if you stand with your arm down by your side and then raise it out in front of you, it's actually the (top part of the) bicep doing much of the work. This movement is called flexion of shoulder,
So biceps brachii flexes both the arm and the shoulder, though it should be said that biceps aren't the main flexor of the shoulder, they just help out!
There are 2 bones in your forearms - the ulna and the radius.
If you stand with your arms down by your sides, with your palms facing forward (make sure that your palms are facing forwards, or you'll get this the wrong way round) then your radius is bone that you can feel running on the outside (thumb-side) of your arm.
(And in case you're thinking, "why didn't he just say the thumb side rather than this palm forward malarky" notice that if you turn your hand over so that it's now palm facing backwards, the elbow hasn't moved which means that the bones have spiralled over one another, making it much more difficult to describe which one is the radius!).
The fact that the biceps attach to the outside of the arm means that the very lower part of the muscle also helps turn your arm so that your hand is palm up. This movement is called supination (think of holding a soup plate!). So biceps assist in supination of the forearm - but only when the elbow is bent.
So a quick recap from what we've worked out from where the biceps attach... the main actions of the bicep when it contracts are:
There are a couple of other actions that biceps are involved in. Remember that the long head sits on the "outside" of the front of the arm, so it helps deltoid move the arm away from the body sideways (a movement called abduction).
Similarly, the short head sits on the "inside" of the front of the arm, so it helps bring the arm back in towards the body after it's been abducted; this movement is called adduction.
So the other actions are:
4. Abduction of the shoulder (long head)
5. Adduction of the shoulder (short head)
The bicep is one of the few muscles of the body that can do opposing movement - here moving the arm both away from and back towards the body (abduction and adduction). We say that the bicep muscle is it's own antagonist.
Around 10% of people have a 3rd head of biceps brachii.
Even weirder fact: a very tiny percentage of people have a 4th bicep.
Apart from obvious times like pulling a muscle through overdoing it with bicep curls, the muscle and tendon of the bicep are involved in a surprisingly frequent number of occasions with arm pain.
Firstly, bicep can get trigger points (those "exquistely tender") small areas of hypertonic muscle. Where trigger points are present in the bicep, they're usually found in the lower part (the distal part- or part furthest away from the torso/shoulder). Bicipital trigger points refer pain upwards: so often pain that's felt in the upper front of the arm comes from trigger points lower down.
That's quite important from a treatment point of view. Someone who has pain in the upper front of the arm might think that deltoid was the problem, when in fact the problem may well lie with trigger points further down the bicep muscle belly.
A second source of pain associated with the bicep is due to inflammation of the bicipital tendon at the origin - in other words, where the muscle turns into tendon at the shoulder.
Remember that the 2 tendons of the 2 heads of the bicep connect to the shoulder. So do a lot of other muscles!
If the bicipital tendon becomes inflamed, that inflammation can often spread quickly to other muscles that connect up to the same place. Generalised shoulder pain often starts with a problem in the bicep. If that's the case it's necessary to treat both where the pain is felt (which could be as far away as the back of the shoulder) and the cause (the bicipital inflammation).
As ever, if you think I can help, give me a call.