For the past few sessions we have become thoroughly familiar with the general structure and posture of the body in a range of variations. Now we're ready to clothe it with flesh, and above all that means the muscles layer, since that defines how things look on the surface.
Understanding What Your Need to Draw
Learning to draw muscles may conjure medical charts in daunting details, but such complexity is unnecessary. We only need to know what shows up through the skin, since that's what we draw: in real life, you'd have to look hard to find someone whose body displays intense muscle detail (basically bodybuilders and some athletes). Similarly, it is only a niche of illustrators who give a lot of attention to muscle details in their work, such as artists for superhero comics.
Therefore it is quite enough to start with a simplified understanding, and move on to medical charts later if one feels the need!
In the diagrams below, I'll be showing muscle groups in color, with a black line to show the forms that would show through the skin (I also show protruding bones that would do the same).
We all have a layer of fatty tissue under our skin, and this softens the look of the underlying muscles. Take an angular object, such as a box, and cover it with thin fabric, such as a bedsheet. Note how the angles look now. Then cover it instead with a thick bathing towel. See how all sharpness disappears? This is what happens in the body.
Now this layer of fat, comparable to that thick bath towel, is generally thicker in populations that originate in colder places, and it's also thicker in females than in males, while males naturally have more muscle mass. Beyond that, an individual's personal story creates infinite variation. You can be very muscular but have a thick layer of fat that makes you look deceptively soft. You can be skinny and have no muscle mass to talk about. You can have an average muscle mass, but so little fat everything looks chiseled (the "sinewy" look). And everything in between.
Quick Notes on Muscle Behavior
A muscle's job is to pull together the points to which its ends are attached. This simple fact can help you deduce what movement a given muscle is associated with.
An active (contracted) muscle bulges and is hard (this is to a light degree: the more effort involved, the more it bulges).
An inactive (relaxed) muscle does not bulge and can be quite limp to the touch.
A musclecan only pull, not push: to return to its original position it needs an opposite (antagonist) muscle to pull in the opposite direction. So most muscles in the body come inantagonistic pairs, andwhen one in the pair is contracted, the other is necessarily relaxed. For instance, if you bend your leg, the muscle whose job it is to un-bend it cannot be bulging, and vice-versa. (You can deliberately contract all your muscles, for instance to block a blow, but no movement is possible while you do.)
Understanding the above means that, no matter what movement you draw, you'll always know the correct muscles that should be bulging. Then you won't end up with something haphazard and anatomically nonsensical. Here's an illustration of how the position of a limb does not determine the state of the muscles, only the movement does:
In the diagrams below, when you see muscle names that are the same color, it means they are an antagonistic pair and should not be both drawn bulging at the same time.
Below are the muscles in the torso and on the back that you need to be aware of. Note also two bones:
Theclavicle bonewhich is always a prominent feature unless an unusually thick layer of fat erases it.
Theshoulder blades, which are prominent unless the back muscles are so developed they cover them up. The visibility of the shoulder blades also varies with arm movements, torso bent, and other movement, so observation from life is useful for this detail.
Obviously, as I'm showing all the possible muscle lines, the result is a very ripped body, whereas softer bodies would show less lines: compare below our original model, with muscles muted to show the lines better, and a more average figure where only a few still show, with the shoulder blades more prominent than the back muscles. Note also less bulky shoulders and a waist that's less thin. This goes for females as well, except that their pectoral muscles are hidden behind the breasts, so they can be replaced by them altogether in drawing.
Using another muscular example, here is the arm:
In an average arm, this underlying structure translates as this contour:
In the legs below, two more bones are to be noted: thepatella(knee cap) and thetibia, which defines the front of the lower leg; indeed there is hardly any muscle there. It's why a kick in the shins is so terribly painful – no cushioning. one can have powerful, hyper-developed calves, but their antagonist, the tibialis anterior, will never grow to the same extent.
Note also that the ankle bone juts out on both sides of the foot, but is higher on the inside. Finally, Achilles tendon, as its name indicates, is not a muscle: though it can be sharply defined in a body with developed leg muscles, it can never be contracted, i.e. bulge like a muscle (its role is to anchor the muscle to the bone, not itself move).
As mentioned above, we all have a layer of fatty tissue under the skin. It can be really thin in our most ripped athletes, and disappears altogether in starved bodies, but even healthy bodies have it – in fact it is what makes us think of a body as healthy, as opposed to "skin and bones".
In addition to this, fat reserves are stored in certain parts of the body, and these are not the same in males and females! As shown below, females store fat in their underarms, thighs and buttocks, while males do in the belly.
Does this mean they don't put on fat in the rest of the body? No, it only means that this is what "fills up" first. A slim female who puts on weight will first notice it in her backside and thighs (aka "can't fit into my jeans!"), then under the arms, and a male will first see a "beer belly" appearing (inversely, when losing weight, these parts are the last ones to go, if they do at all.)
Then if the weight increase continues, the fat under the skin grows along with the fat reserves, and we see the weight piling up all over the body. Finally, in extreme cases, there is inflation everywhere the skin is willing to stretch.
The tendency to store fat increases when we hit our forties.
Post-menopause, a woman's fat reserves are redistributed to the belly and follow the male pattern.