Try this out right now. Point at something in front of you with your index finger. Now flip an imaginary rival the bird with your middle.
Now stick out our pinky, like you would to tell your primary school teacher you need to pee. Now stick your ring finger out, like you’re showing off an imaginary ring. Notice the difference?
Notice how it’s harder to splay out your ring finger on its own than it is the others? Ever wondered why that is? It’s not just sticking them out either. Try stretching all your fingers out and then bending them one by one. Once more, you’ll notice it’s hardest to do this with the third finger. To understand why this is, you first need to know a little more about the musculature of the hand and forearm.
Your thumb has the most flexibility of all the fingers on your hand, and you can shift it irrespective of how the other fingers are place, because it has independent muscles serving it. The thumb has multiple little muscles around its base that aid its movements, and another set of muscles in the back of the hand and forearm to help straighten it from a bent position.
The little finger actually moves easier than the middle and ring fingers. That’s because it also has independent muscles for some movements. However, it also relies on muscles shared with the other three fingers for some actions, thereby limiting your control.
All four fingers are flexed by two muscles in the forearm called “long flexors” and one set of muscles in the hand called lumbricals. But the reason your index finger has the best movement of the lot is because one of the forearm muscles has a separate tendon connected to it. Basically, the same muscles bends all the fingers, but this tendon lets you bend your index or straighten in independently. In addition, though it shares another forearm muscle with the other fingers, it also has a separate extensor muscle allowing you to independently point even as you make a tight fist with the rest of your hand..
It’s thanks to these independent extensors in the thumb, index, and pinky fingers that you can rock out at a concert.
Unfortunately for the ring and middle fingers, they have no independent flexors or extensors. Instead, they move only with the muscles common to all fingers. That’s why, for instance, when you try to stick out only your ring finger you feel a pull in your middle and pinky as well.
So if both use the same set of muscles, why then is the ring finger harder to move than the pinky? Well, that answer may lie in your brain rather than your muscles. You see, the fingers are connected to the brain through two nerves. The radial nerve connects with the thumb, index finger and one side of the middle finger, while the ulnar nerve connects with the little, ring and the other side of middle finger.
It’s this branching between these nerves that causes the dependence of the fingers on each other for movement. Because the nerves for the ring and pinky finger are intertwined, it becomes harder to move each of these fingers separately. The same things happens between the ring and middle finger. However, your middle finger moves much more easily because it’s getting two sets of signals.
This combination of handicaps to the ring finger by both your musculature and your nerves is why it’s so hard to move it on its own.