Our fingers don't have any muscles. Not a single one, nada, zilch.
So how can we do this? When you flex your arm, you see
that this muscle, the biceps, contracts. Whether the muscle is visible or not, we know that
there's a muscle here which contracts. And if we do the look at flexing our fingers,
we will not find not an equivalent of the biceps here. And for good reason:
there are no muscles in the fingers. What you grab here is no finger bicep,
it's fat and skin, not muscle. So I'm not saying this to get you
to put your fingers on a diet—in any case that would be useless since we cannot
choose where we lose weight... We cannot say “Today, I'm losing weight in my fingers.”
I'm talking about it because I think it's crazy. How can we move our fingers, with dexterity
as well, if there isn't some kind of a finger bicep inside?
We are going to do lots of little experiments with our hands and arms,
that you can do as well, so bring your children,
your spouse... it will be more fun to do it together.
If we look at an anatomical chart of
the hand, we can clearly see that the palm has muscles. They are used for many things,
in particular to spread the fingers or bring them closer (abduction and adduction). But also to
flex between the palm and the fingers. But you'll notice that the fingers are completely bare.
On the other hand, what we also see is that even though the fingers are devoid of muscles, or
rather, of the meaty part of a muscle, the part that contracts, they are connected
to these muscles through strings, of cords, called tendons. So
we have many muscles which operate our fingers, it's just that instead of being there,
they are there. So I repeat because I find it crazy: our finger muscles are in our
forearms! To convince yourself of this, you can flex and extend your fingers while feeling your
forearm, and you will feel that there is action over there. Go ahead, try it! At the front we have
all the muscles involved in flexing the fingers and wrist, and at the back
we have the muscles involved in extension. It is a good thing that the muscles of our
fingers are relegated to the forearms. This allows the fingers to remain slender and
consequently, to carry out fine movements. If we had muscles in our fingers, our hands
would get bigger simply by using them (muscle growth) and limit us in our movements. We
would just have big useless paws. Someone who has a strong grip,
strong hands, is often someone who has big forearms. So now that we know
that the muscles are there, we will be able to play a little game. And this little test is probably my
favorite of the whole video, you absolutely have to try it out. Put your arm upright,
while keeping your muscles relaxed. Let your hand sit at the top.
Don't contract your muscles to keep it there, it should stay there by itself. If you press the
inner side of your forearm, and that really you don't do anything with your muscles,
you will see that your hand... falls. I haven't done anything to lower my hand,
it's only because I pressed a bunch of muscles related to flexion of the wrist and
fingers in the forearm that ultimately, it's like I'm pulling on the muscle, which makes
my hand drop. Those who follow me on Instagram know we played around with it a lot this summer.
You might find it ridiculous, but it totally fascinates me.
I find it different depending on where on my arm I press... It's so funny.
Okay but that is just the tip of the iceberg. If a muscle is
relocated, that implies a certain layer of additional complexity that makes the
whole thing even more interesting. Basically, our fingers work like
puppets that we operate with cables, from the forearms. Since
our hands are glorified puppets, it means that we have a string (the tendon) that runs
from the finger to the forearm. And when the muscle contracts, it pulls on the finger.
We can control our fingers from the forearm. But we have a big string right in the middle,
the tendon. Frankly it looks like a bow and all we need are
arrows to shoot... arrows with our fingers' tendons...
It sounds like I'm just making a joke
talking about bows and arrows but that's really what they're called. If the tendons in your
fingers were ripped off like this (yes, it can happen... and no, that wouldn't be good),
it's called bowstringing. And I'll spare you the photos, your imagination should be enough.
For a puppet, it's okay for its strings to stick out, but not for us. It wouldn't be
convenient. We don't want there to be a rope hanging out like that. So how do we fix it? How can we
keep this finger flexing ability while avoiding that string right in the middle?
I can't hear you but I'm sure you already have the right solution in mind:
stick the tendon along the finger.
I've just added something to hold the tendon
against the finger so when I pull, the finger flexing feature still works.
Obviously, we would have more rubber bands along the finger but this is just a model,
okay? It's not a perfect model for reality. Speaking of reality,
this is exactly how it works. Obviously these aren't rubber bands in reality,
but an anatomical structure which I had no idea existed until a few years ago:
pulleys! So these are not the pulleys you find at the crafts store,
but human pulleys. They are fibrous bands which are there to press the tendon
against the bone. I only put one here but there are more all along the fingers... If we look again
the anatomical chart, our fingers look like mummies precisely because of all the pulleys
which press the tendons against the bone (while still letting it move). We solved our problem.
But so far we've only looked at one finger. It goes without saying that we will need one cable per
finger. But what is most surprising... is that these 4 strings are all connected to
the same muscle! It's called the deep flexor muscle if you want to know its pet name. And
if you find it hard to believe it is a only one muscle, try this. Hold your finger,
the index for example, like so. We are trying to isolate the flexion of this section of my finger.
It works, I can only move the fingertip. But that's not where you should look.
Watch my other fingers. I am not moving them, I am not trying to
control them voluntarily. I'm only controling my index finger. And yet. They are
reproducing the same movement as my index. Not in the same intensity, but hey,
there is something. That’s because they’re connected all to the same muscle. So obviously, when one
finger bends, the others bend too. That said, outside of this specific example where I'm blocking
my finger, we know that we can bend each one of our fingers independently. That’s because yes,
it's the same muscle, but each tendon is connected to a sub-part of that muscle, to a muscle bundle.
It gives them a certain independence. And then also, when our hands are free,
we have many muscles that act in synergy to provide us with exactly the movement that we
want and that gives us independence for each of the fingers. You may have noticed that I've kept
the thumb apart (although it works the same as the other fingers), simply because it
acts like a diva by being oriented in a different direction from the others. This is something
that we benefit from: because it is oriented differently, we get to grip things.
Without it, our fingers would be as useful as our toes to open a pot of jam.
Not great. And clearly, the thumb is well aware of its hierarchical superiority
to the others. You know what the set of muscles at the base of the thumb is called? It's called
the thenar eminence... pretty pompous, in my opinion. I call it the thigh of the thumb, it brings it back
down to earth, that'll do it good. Okay, with all that, we start to have a pretty functional
hand. We have four tendons. But I think you will agree that we are still
lacking a bit of control in the fingers. We have two articulations and a single cable… So that means
that we are unable to get into this position over this position. The bend between this
part and that part remains the same, but it is the flexion between this part and that one
which is different between these two positions. So how do we fix it? I'm sure you've already found
the correct answer: let's add more cables. It's that simple. So I just added
a cable at the level just below, and this one is also pressed in line by all the pulleys along the
way to keep it in place. It is also connected to a muscle, and it will be the same muscle as for
all other fingers. Basically, we have two flexor muscles in the forearm for all of our
fingers: one for flexing the tips of our fingers and the other to flex the middle part
of our fingers.
So we've ended up with 8 cables: 4 for the deep flexors and
4 for the superficial flexors of the fingers. And that's it. We've got ourselves a hand that
can close. But not reopen. To reopen, you need other muscles, extensors this time,
which are on the back of the hand and the back of the forearms. And those muscles,
unsurprisingly, are called extensors. But I think you are starting to understand
the logic. Moreover, this system works great as long as you don't
overuse your fingers. If you pick up rock-climbing, (I take it as an
example because it is probably the sport that's most conducive to the overuse of fingers...
and the creation of bruises too) ;)
After a few weeks of climbing,
you will feel muscular adaptation. Your forearm muscles will have adapted
to the fact that now you hang in the air a lot and they need to be stronger.
Cool. But that's the muscles. They're super efficient, they adapt very quickly
within about 3-4 weeks. But tendons or pulleys (which are physiologically
similar), oh no no no... before all the tendon structures in your fingers increase
their resistance to a load, you will need years of practice (3 to 5 years) for the hands,
specifically in rock climbing. And by the way, we can extrapolate it to the rest of the body.
When you hurt yourself right after
picking up a physical activity, it's more often because you went too hard,
too fast. Your muscles were able to handle the increase in effort but your tendons haven't had time to
adjust to their new constraints. And that can turn into tendonitis. And just as they
are slower to adjust to overload, they are also slower to repair themselves. In short,
tendons are real wimp. So let's avoid getting injured.
We've talked about what I wanted to tell you about the biomechanics of the hands,
I hope you've found it interesting
and I will add just a few notes now, maybe a bit more disjointed for those among you who are most interested.
First point: every time I've said the word "muscle", I meant in the common sense of the word.
In general, when we think of a muscle, we think of the red meaty part that
gets bigger when you contract it. However, in the real medical terminology, this part is called
the muscular body and forms part of the muscle in the same way as the tendons are part of it. So I should
say "there is no muscular body in the fingers" rather than "there are no muscles in
the fingers", because it is a misnomer, since tendons are technically part of the
muscle. Second point: if you are like me and you have an office job,
our fingers are often a little chubby. People who do more manual work,
you can see it, they have big stocky hands and as for their fingers, they probably wouldn't
be able to grab onto their fat. That doesn't mean that their fingers don't have any fat;
their skin is probably callous and much thicker than ours. These people
do not have muscular fingers, as we've seen, since there is no muscle 'meat'
in the fingers. Last point, I'll give you a little tip to make the distinction
between tendons and ligaments (because I am one of those people who took a long time to
remember the difference between the two). A ligament connect two bones together (LIgament - LInk),
whereas a tendon does not connect bones but allows to stretch a muscle (TENdon - TENsion).
This is the end of the video, I want to thank Dr. Alexandre Pegot for answering my questions
and I hope this type of content has made you want to...
subscribe to the channel. Bye!