Human Anatomy for Animators - drawings by kimsuyeong

Anatomy For Animators 01 – The Human Skeleton and Muscles

Most of us are taught anatomy in at least one class in school (mostly before the frog dissection). Out comes the plastic skeleton on his rickety little trolley base, grinning from ear to ear. But we never really truly remember (or use) the information. We never understand the true nature of basic human anatomy when we sit down to animate. Animators tend to be very much creatures of habit. Sadly if it’s not known, or if the information is not clear enough, (or doesn’t have any drawings) we tend to discard the knowledge faster than trying to animate a one legged horse.

The posts on my blog that have been the most popular have been about anatomy for animators; muscle and bone relationships, and how they apply to animation. For the last four years, I have been trying to merge these into an interesting format with pictures. So when DJ Nicke asked me to write articles for Animation Salvation, I couldn’t refuse!

Human Anatomy For Animators

A series of Articles Exploring Human Anatomy from the Perspective of Animators

The human skeleton is fascinating, since we are one of the very rare animals that stand upright (bipedal), yet we do not have a working tail to balance. Gravity is essentially an enemy to us.

We tend to be more efficient energy wise as we have arms to carry stuff and only two legs that need to be powered to walk. So we have a really interesting, gravity assisted way of walking; and running in a state of perpetual falling and catching ourselves on the next step.

Anatomy study Upper Arm by kimsuyeong

Ok, so now for the dry stuff:

There are six major functions that the human skeleton, the three that we need to know as animators: support, movement, protection (the others are as follows; storage, blood cell production and endocrine regulation). Just to freak you out a little, there are 206 bones on average in the adult human body (most of them in the hands and feet).

Actions of the relation of muscles and bone; we work on a pivot and hinge system bone wise with muscle being essentially a pulley system.

Skeletal muscles are often named after the following characteristics:

  •  Number of origins: Biceps, triceps, and quadriceps indicate two, three, and four origins.

  • Location of origin or insertion: The sternocleidomastoid names the sternum (“sterno”) and clavicle (“cleido”) as its origins and then the mastoid process of the temporal bone as insertion.

  • Location: In addition to its origin or insertion, a muscle name may indicate a nearby bone or body region.

  • Shape: The deltoid (triangular), trapezius (trapezoid) and rhomboideus major (rhomboid) muscles have names that describe their shapes.

  • Direction of muscle fibers: The terms rectus (parallel), transverse (perpendicular), and oblique (at an angle) refer to the direction of the muscle fibers with respect to the midline of the body.

  • Size: Maximus (largest), minimus (smallest), longus (longest), and brevis (shortest) are common suffixes added to muscle names.

  • Action: Terms such as flexor (flex the hinge joint), extensor (extend the hinge joint), abductor (away from the body), and adductor (return to the body) are added as prefixes to muscle names to indicate the kind of movement generated by the muscle.

Why should you take the
skeletal structure into account while animating?

It is the basic structure of any basic living creature and therefore it will only move in accordance to the hinges or the rotators that are put in place to allow the freedom of movement within the confines of gravity.

Ball & Socket Hip Joint

Ball and socket joints: rotate until constrained either by the pelvis or the shoulder blade and clavicle.

Knee Hinge xray

Hinge joints: arc until constrained by the particular end of the joint which locks into place and does not allow over movement.

Cervical Vertebrae

Vertebrae: held in place by sheaths of muscle, keeping the vertebrae in place while allowing the column to pivot.

 So one side is the pulley and the other side is the counter stretch.

Involuntary Muscles

  • Involuntary muscles are muscles that are not controllable consciously, and instead contract due to unconscious impulses sent by the autonomic nervous system or certain specialized cells or hormones.

  • Both smooth muscle and cardiac muscle can be classified as involuntary muscles.

  • Smooth muscle is comprised of spindle-shaped cells that have no striations and is found in numerous locations throughout the human body.

  • Cardiac muscle is striated rather than smooth, and is found only within the walls of the heart.

Skeletal Muscles

Everything else is comprised by what is called skeletal muscle and they are like giant rubber bands with the elastic bands running in what ever direction they need to contract in. So you know when you have stray threads in a piece of clothing? And you pull it and the rest of the fibers get bunched up? That is exactly how muscles work, if they just contracted like rubber bands we would never get them back to a semi normal state.

I have found in observation that
people tend to favor one side of their body in movement

So that side tends to be more developed than the opposite. This tends to mean one side is a little shorter (not by much). You should make sure that you take this into account when capturing life action movement.

Have you played watchdogs (the video game)? If you look closely, (and I had to point this out to a non animator friend of mine) you can see that the run cycle isn’t even. Since it’s all mo capped, the non dominant foot stays on the ground longer than the other, leading to the run cycle cutting off the end of the animation. This results in a very funny non limp in the run cycle. Here is a video where you can see this for yourself:

 

This concludes our first lesson in Human Anatomy for Animators. Now that we understand how the skeleton and muscles affect the movement of the human body, we can look at those movements in more detail.

Human Anatomy for Animators - drawings by kimsuyeong

Anatomy For Animators 02 – Anatomical Movement

The body is interesting, even in a resting state, as the body doesn’t ever truly stop. There are always subtle movements: shifts of weight, breathing, the unconscious balancing act, conscious feedback of where our limbs are at any given moment, blinking, and thought.

We are going to start with Breathing

To understand breathing, you have to know that gases travel from areas of higher pressure to areas of lower pressure.

Intercostal muscles of the lungs and ribs
  • In the first stage of inspiration (breathing in): the diaphragm contracts and moves down and the intercostals contract. That means the rib cage rises and expands outwards where the diaphragm contracts. The larger volume in the lungs means lower pressure and the air flows in.

  • In expiration (breathing out): the diaphragm and intercostals relax so the rib cage shrinks back to a normal state. This returns the pressure to normal and the air that has been breathed in gets expelled as the lungs return to a normal state.

Intercostal muscles of the lungs and ribs, with Diaphragm

Let’s Move Our Anatomy!

What about movement and locomotion? In order to move, the body has to go from a rested state into movement. That’s when we need to know the four contraction states of muscle. Skeletal muscles are the ones that really concern us and are the muscles that cover the entire skeleton. Without them we could not move and they make up around 50% of our body weight:

  • In concentric contraction, the force generated is sufficient to overcome the resistance, and the muscle shortens as it contracts. This is what most people think of as a muscle contraction.

  • In eccentric contraction, the force generated is insufficient to overcome the external load on the muscle and the muscle fibers lengthen as they contract. An eccentric contraction is used as a means of decelerating a body part or object, or lowering a load gently rather than letting it drop.

  • In isometric contraction, the muscle remains the same length. An example would be holding an object up without moving it; the muscular force precisely matches the load, and no movement results.

  • In isotonic contraction, the tension in the muscle remains constant despite a change in muscle length. This can occur only when a muscle’s maximal force of contraction exceeds the total load on the muscle

We have to be observers and notice things that most people never notice.

As animators we need to observe and pay attention to the movement when there is no movement. We need to observe the distinction between conscious movement, unconscious movement, and movement caused by our anatomy.

First stage of movement:

Muscles contracting involuntarily, trembling of limbs, air forcing the lungs to expand and contract, the blood pressure in arteries moving the fingers – when we are still our bodies are not, the autonomic systems in place make sure that we stay alive.

The movement before the action (Anticipation):

The lungs increase in volume, breathing quickens, eyes start moving faster as they blink in anticipation and start focusing where the body will be moving to, muscles contract as the brain informs them that the body will be moving – This is not just for the preparation of an Olympic sprint, but even for the body simply getting out of the chair or starting to walk.

The action itself:

The muscles start contracting from the origin of the moment i.e. the muscles around clavicle and the shoulder drive the action of throwing the ball, the elbow starts engaging as the muscles in the upper arm pull the the hinge up, the tendons start pulling fingers tight around the ball as the they start contracting from their origin behind the elbow, the muscles above shoulder and the clavicle engage even more to pull the the arm straight up. The body has started to slow the breathing as the blood starts flowing faster with the oxygen rich blood, the heart starts to beat quicker to keep up the supply to the muscles that are working. The eyes hold the gaze as the body gets more focused in the activity. Then the muscles engage to throw.

The movement after (Follow Through):

The muscles tremble and spasm slightly as they stop contracting – they have done their job, performed the task that they were asked to by the brain. The body slowly returns to normal heart beat rhythm as the lungs return to the normal breathing rate. The muscles in the face might twitch slightly as the eyes track movement of the ball waiting the indication to move the body into a emotional state depending what the ball does.

Weight, Mass, Momentum

Though it would be interesting to talk about how muscle mass affects the body, now in animation terms you say that mass=weight, and if there is a heavier (i.e. ogre) model it walks slower… right? In real life it is not so straightforward.

Let’s take for example a man with big muscles; he appears to walk slow, right? If we could see his muscles underneath his skin, they are in a contracted state. Muscle contraction happens all the time, but exercise can cause a muscle to stay in its contracted (shortened) state. When it is like this, a muscle will not move freely from contracted to a relaxed state. It looks like the man is stiff in his stride because that is what is happening; the muscles don’t relax and stretch away from the body. That is why he is walking slower; he is more bulky, so the mass is more than the weight in this instance, as muscle weighs more than fat.

What happens if muscle stays in a contracted state? The muscle then stays in a shortened state resulting in loss of range of motion for that particular muscle and can result in changing the way that the body can move.

The man with more fat than muscle has to swing his arms further and moves the torso quicker to get the momentum up to walk. His legs are always trying to catch up underneath the body in smaller steps than normal. The short steps are trying to balance the body mass more than a person of a smaller size. People that carry more weight don’t actually have less muscle, as you might think. They have to carry more weight with every step. It seems like the fat man is walking rather fast; which he is. It is just taking him longer to get anywhere. He needs to expend more energy with each action, mass=weight with the weight of fat being more than the weight of muscle on this person.

The skinny man seems quite fast in movement to the others. He has no real mass (muscle or fat) and is quite skinny. It doesn’t take him long to move as the mass is not constraining his movement as much. Take note of this: if for any reason the muscle outweighs the fat or vice versa, the action would be slower as the muscle has to move the fat and the fat breaks down to feed muscle so therefore the skinnier guy would have a harder time moving if these weren’t equal.

You are probably to the point in your animating that you have have the idea down that timing of the movement has to originate from the torso when moving… legs, arms, torso and the head have to take their direction from driving forces, thinking and balance as well as gravity and physics.

But have you thought that because things weigh more in the body that they will take more time to respond to the movement and the force of the action? Swing your arm around.. and notice that the heavier upper arm even though the movement originates from shoulder will have different timing and different response to the force of movement compared to your very light hand.

Anatomical Animation and Movement

Hopefully that gives you a solid foundation of anatomy for your animation, and an understanding of how your anatomy affects the way you move.

In our next article, we are going to look at the anatomy of walking.

Giving Your Characters the Illusion of Life

What is it that gives an animation the Illusion of Life?
You could say it’s the pose, because the pose can tell you what the character is feeling.
You could also say it is the timing, because you can set the mood of your character through the timing.
And yet, when you watch great animation it feels like there is something more.

What is that *more*? How can you achieve it in your animations?


In order to demonstrate, I’d like to breeze through the animating of a scene:

  • First, I get the storyboard, the audio track, the character model sheet etc from the
    director
  • Next I pose out and thumbnail the action of my scene
  • Finally I keyframe it out on the computer with the proper timing

This is the general process that most of us go through when animating, but I’d like to suggest a few more steps to really add that ‘Illusion of Life.’ Now think about what life is. Now there are
about 20 definitions over at Merriam-Webster, but I’m talking in specific about definitions 6 and 11:

 6 : a way or manner of living
11 : the form or pattern of something existing in reality

We want to give our characters the Illusion that they exist in reality! The illusion that they have developed their own manner of living!

How do we give Our characters the Illusion of Life?

Well, you should be talking with your character lead if you have one, and/or the director.
Discuss character traits:

  • Does he nervously dart his eyes around and act like Woody Allen?
  • Did he have a traumatic experience in childhood that makes him walk through every door backwards?

There are some strange personality quirks that people have in real life, and you know what this expresses? That’s right, that they exist in reality!
They have lives outside of their interaction with you!

A great example of this is Peter Lorres character Ugarte from Casablanca

Peter Lorre interacts with Humphrey Bogart in the movie Casablanca

Peter Lorre interacts with Humphrey Bogart in the movie Casablanca

Just look at that face, the way he’s trying to mimic Rick’s (Bogart’s) confidence. And yet he always, even if momentarily, reverts back to his worried, weasely self.

That is a great character and one that lives on in your memory! But what made it a great character? Well, it was the fact that he existed outside of his scenes so well.

We never saw him kill the German Couriers or get the papers, and yet we knew he did it by the way he acted! The way he held his body (posing) and the manner in which he moved between poses (timing).

Another great example of Ugarte’s character is the way he enters the Film. He could just walk into Rick’s Cafe, but that wouldn’t tell us very much about him as a character. Instead he ‘weasels’ in between an arguing customer and the door man with a passing “Hello Rick…”!

From his first frames in the movie we understand what kind of character he is! Plus, the entire time he is talking with Rick, we sense that he and Rick have history together and Ugarte really wants Ricks approval.

We get this, not so much through dialogue, but through the posing and timing of Ugarte’s movements. There is a great gesture Ugarte does at about 9:50 into the film which is very odd, and yet tells us so much about his personality!

These things are what give characters that Illusion of Life!

“But we can’t compete with live actors!” you say.
Guess what? Peter Lorre, Humphry Bogart, these people are dead, and yet their characters live on in the same form that ours will: 2D images mixed with sound.

We have the same tools as any actor, real or imagined. If we use them properly, we will be able to create characters that truly live, maybe even longer than we will!

So lets go back to our list and see what we can add:

  • First, get the Storyboard, audio track, character model sheets etcetera from the director
  • Next, talk with the director and your character lead about the personality of your character
  • Discuss with the lead and any other animators possible character traits, poses, nervous ticks
  • Sit down and imagine your character acting your scene out in your mind, let it run free at
    first, then subtly direct it
  • Thumbnail your characters action out on paper
  • Take these thumbnails first to your character lead for approval/suggestions, then take it to
    your director for approval/suggestions
  • Now set your keyframes, and MAKE EVERY FRAME COUNT
    • Everything from the way your character enters and exits a scene, to every pose they hit, to the timing between the poses should have a purpose and tell us something about that character.

Well, I hope that helps a few of you. And if anyone has any further comments on this topic, please share them! Until next time…
Happy Animating!
-DJ