Human Anatomy Fundamentals: Balance and Movement
This post is part of a series called Human Anatomy Fundamentals.
This is our last session working with the basic structure of the body before we start clothing it in flesh. We have seen how it is proportioned and how those proportions vary within limits; now we’ll see how it counters gravity with posture – and how far posture can be pushed before it falls over (or, on paper, looks out of balance).
Balance: How to Stand (and Fall)
The body’s Center of Gravity (CoG) is roughly behind the belly button. The body is supported by whatever part touches the ground: generally both feet, but it can be one foot, two feet and one hand, two hands, etc. The Center of Support (CoS) is the mid-point between those points of contact with the ground, whether it’s a single point, or they form a line, a triangle or a square.
The alignment of CoG and CoS determines balance, both in real life and on paper, and this operates differently depending on whether the body is still or in motion.
Balance in Stillness
Picture a vertical line shooting up from the CoS. The body is balanced if the line runs through the CoG. Think of it as balancing two cans on top of each other. They can only be slightly unaligned before the top one falls over.
Even if the body is holding a puzzling stance, most of the time you’ll find that the CoG is still aligned with the CoS, holding it all together.
It is very difficult to hold an unaligned position like the one below for more than a few seconds. The alignment must be reestablished, either by moving the CoG back in line, or by moving one foot to re-position the CoS – otherwise a fall is inevitable.
More on the Center of Support
At this point I must explain that my original definition of the center of support, as mid-point between points of contact, was actually a simplification: locating it is not always such simple math, but actually requires some observation and intuition, as points of contact with the ground don’t necessarily bear the same amount of weight! The center of support is closer to the side that carries the most weight, proportionately to how much weight it carries. Classic example: when you’re standing around, you may find yourself putting all your weight on just one leg (left, below). Notice, when you do this, how your body is positioned over that leg, and how its move back to the center if you distribute your weight equally between both legs again (right, below).
We probably spend more time distributing our weight unequally than we do equally, and we perceive this as more natural: the best figure artists are those who capture this balanced-imbalance and thereby draw relaxed-looking characters, whereas someone who applies the law of balance mathematically ends up with stiff, unnatural and above all non-dynamic looking characters.
Below is an illustration of this dynamism: the character on the left stopped mid-stride, when she had transferred her weight to her front foot and was about to lift the rear foot, which as a result carries little weight despite touching the ground. Her CoS is therefore close to her front foot. Reading-wise, it is because most of her weight is clearly on her front leg that we can tell she’s stopped in motion, as opposed to what is shown in the medallion. The figure on the right shows a CoG that’s only slightly off-center, but this subtle visual clue in an otherwise symmetrical stance informs us that the weight is shifted slightly to the left leg, saving the figure from looking like a diagram in a martial arts text book.
An additional “complication” is the muscle factor – countering gravity with strength–, which is why specially trained people astonish us with stances that should be impossible. However, while in real life we can watch crazy feats and have no choice but to believe what we see, they can fall rather flat on paper and look like the drawing is off. It’s important for an artist to learn to draw whatlooks right, rather than what is right but looks odd. The gravity-defying postures below are all genuine, but can you accept them as such without seeing actual photos?
That said, the muscle factor comes into play in less extreme ways all the time. For instance, the figures below are carrying the same weight. The taller one, having plenty of muscular mass, can carry it at arm’s length even though this shifts the body’s CoG. He has enough muscular power for that not to affect him. The smaller figure would topple right over, so he has to hold the weight close and lean backwards to preserve the original CoG as much as possible.
This sounds complicated when described, but we do this all the time without thinking about it, and again, the ability to internalize or feel what you’re drawing makes it easier to put it on paper without having to calculate the positioning of various centers!
For a body in motion, we look at things differently. Imbalance is the motor of any motion, in fact you could say motion is a controlled loss of balance. So for this we are going to set aside these two centers as less relevant, only bearing in mind that the further a stance is from the idea of balance described above, the faster, more dynamic, more dramatic the movement it expresses. The following are pointers for kinds of movement that often come up in illustration.
Running or Moving Forward
The faster we run, the more we bend forward. The rule here is that, at its fullest extension, the front foot must hit the ground in alignment with the head (or close). If the head is way ahead of the legs, this is an uncontrolled run that can only end flat on its face!
Contrary to moving forward, the body leans backward, at least if we’re trying to move faster than a walk. Yet there is very little range here. The heel needs to hit the ground in alignment with the back-leaning upper body, and if you try you’ll see you can only take a very short step back this way without stopping the movement altogether.
Whether you’re throwing an object or a punch, the movement is the same and it is invariably followed by stepping forward with the leg opposite the arm used to throw. This is the natural, unconscious reaction to stop the body from toppling forward following a powerful throw. Martial artists and similar trained athletes sometimes step forward with the same-side leg, but bear in mind this is a trained and conscious movement, not something you’d see in a bar brawl and such. Here’s a trick to make your throwing look more dynamic, or captured in the heat of action: draw it as the foot steps forward but before it actually hits the ground, as that (as shown here) captures the end of the motion.
When catching something, blocking a punch, or dodging, we take a step back to lessen the impact of the coming force – or because the impact forced us to. Only a trained fighter would step forward while blocking, it is completely unnatural. Note that this is a movement we do not want to look fluid or dynamic.
Jumping vs. Falling
This one’s a bit obvious, but the difference between jumping (controlled, will land well) and falling (uncontrolled, will end in pain) can be subtle, as in the top row. The first pose feels like a jump with a proper landing coming up. This is because the feet are suitably placed under the CoG to achieve a balanced alignment upon landing. The second pose is the exact same but I rotated it slightly so the feet can no longer catch the CoG. What a difference! It no longer looks controlled at all. The last two are even worse and even more expressive of a disarrayed fall.
Below are three distinct kicks: a “natural” or untrained one, a football kick, and a martial arts kick.
When someone randomly kicks something, the natural reaction is to lean back to oppose the strength of the kick, and so remain standing. This creates a high risk of falling on one’s bottom if the kick is too strong, or the footing not firm enough! But this is what we all do innately, and it is quite impossible, after such a kick, to move in any direction without first bringing the raised foot back to the ground to regain full balance.
The football kick sketched here, while not the only variety by any means, is distinctly designed for the player to not lose balance despite its power, and to be able to continue running without a moment’s pause. You can see it in the forward bend of the body and the swing of the arms to balance it; when that foot returns to the ground the whole body will already be in a running posture. The martial art side kick shows similar control, with a slight deliberate imbalance: you can see from the forward position of the CoG that the body is pressing forward. This fighter is counting on the impact with his target to stop what would otherwise be a fall, and putting all his body weight into the kick to give it its power. Do note that this abandon is reserved either for an inert target (sandbag) or an easy opponent; when sparring with a skilled opponent, he would take much more care not to push all his weight forward, as a dodge or grab from the other would sweep him off his supporting foot altogether.
- Observe people, and photos capturing athletes in motion, with the above notions in mind. To preserve them in your mental library, sketch additional details you may notice in the body.
- Practice sketching people in various still postures without reference. Do they feel balanced? If not, locate your two centers and check their alignment.
- Trace the basic structure over some photos of athletes in motion. You’ll notice the result really lacks dynamism, which is inevitable when tracing from photos. But basing yourself on these, redraw the postures while exaggerating the movement to make them properly expressive.