Hands are notoriously tricky to animate, but when done correctly, it adds a lot of detail and believably to your performances. But to begin creating nice hand poses, it is important to understand their internal structure.
Bone Structure
There are three different types of bones in the hand:
Carpals
Metacarpals (plane joints)
Phalanges (rotate like hinges; only one direction)
*I'll be referencing these bones in my explanation of the muscles below, so if needed, you can refer back to this image for clarification.
Each set of bones also has a specific type of pivot or joint, which determines which direction(s) it can rotate.
*To learn more about the types of joints, see my previous blog post
Hand Ligaments
Ligaments are flexible connective tissue between two bones, usually holding together a joint. In the hand, these prevent sideways bending of the joints.
The volar plate is an important ligament in the hand because it keeps the finger joints from hyperextending. However, enough force can cause a rupture in the volar plate, which is why a finger can be bent at an odd angle when broken. Problems with the volar plate could also occur due to disease.
Hand Muscles
There are four main muscles within the hand that control how the fingers rotate:
Interossei
Lumbricals
Thenar (controls the thumb)
Hypothenar
Interossei
The interossei muscles stretch from the metacarpals to the base of the proximal phalanges, with three on the palm side of the hand and four on the back side of the hand.
The muscles on each side of the hand have a different purpose. The ones on the back side of the hand allow you to abduct your fingers (aka, spread them apart). Conversely, the interossei on the palm allow you to adduct your fingers (aka, bring them closer together).
Lumbricals
The lumbricals are located on the palm side of the hand, one for each finger (aka. four in total), stretching from the flexor digitorum profundus tendons to the extensor hood (found on the outside of the hand on the proximal phalanges).
The lumbrical muscles have two different purposes. First, it allows you to bend your fingers forward at the base of the proximal phalanges. It also allows you to bend your fingers upward from the base of the intermediate phalanges.
Thenar and Hypothenar Muscles
The thenar muscles are three short muscles at the base of the thumb, with the hypothenar muscles being a mirror image of this, located below the little finger.
These muscles allow thumb opposition, which is the ability to turn and rotate the thumb to touch each of the other fingers. This is how your hand is able to grip and hold objects.
The muscles give a good idea of how the hands move, but a great followup to all of this information is creating appealing hand poses. Look out for my post on that soon!
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