LESSON - General Anatomy Primer (Patreon)

This is a general primer of anatomy, showing the names, positions, and shapes of the major muscle groups of the body

NOTE: This is NOT a substitute for anatomical studies. You will still need to do your own studies (ideally using photo references) to build your own knowledge of these individual muscles. 

This is only a primer to get you started with the basic knowledge + some notable tips. Feel free to refer to this for basic information when you’re having trouble with your studies.

Introduction

When artists talk about “muscles”, we generally mean skeletal muscle, as opposed to other types of muscle (smooth muscle and cardiac muscle). Skeletal muscle is the stuff that moves the human body.

Every muscle is made up of strands or fibers that go in one uniform direction. Each end of the muscle is anchored on a bone, or on another muscle/tendon.

A muscle can only do one thing: Pull. It does so by contracting, i.e. compressing itself into a shorter, but bulkier state. When a muscle pulls, it can only do so according to the direction of its strands.

Muscle Interaction

In many cases, there’s a pair of muscles/muscle group pulling on opposite sides,

This allows for Flexion (bending) and Extension (straightening) by alternating which muscles contract and which muscles relax. This is one common kind of Muscle Interaction.

When two or more muscles are acting opposite of each other, they’re known as “Antagonistic Pairs”.

Other notable terms in muscle interaction are:

• Adduction: movement towards the center of the body
• Abduction: movement away from the center of the body
• Medial rotation: rotation towards the center of the body
• Lateral rotation: rotation away from the center of the body
• Pronation: facing down
• Supination: facing up

Neck

Primary components:

• Sternocleidomastoid (SCM)
• Trapezius
• Throat
• Platysma*

The Sternocleidomastoid overlaps with the trapezius, and the shape of the neck varies greatly depending on the angle and the movement of these muscles.

The Platysma is a thin sheet of muscle that covers most of the front of the neck. It’s commonly visible when someone is cringing.

Front Torso

Primary components:

• Trapezius
• Pectorals
• Deltoids
• Abdominals
• Latissimus Dorsi
• Serratus & Obliques

The Pectorals are probably the most prominent muscle in this area. One end of the pectorals is anchored on the Humerus (upper arm bone), while the other end fans out to attach to 3 different bone areas: the clavicle, the sternum, and the ribs.

Different parts of the Pectorals control different kinds of movement. Be mindful of this when posing your character’s chest.

The Deltoids have some overlap with the Pectorals. Also, when the arm is fully raised up, it’s not uncommon for a part of the deltoids to peek out of the other side, next to the Lats.

Latissimus Dorsii, aka the Lats, are primarily a back muscle, but it shows up prominently on the sides of the torso, especially when the arms are raised up. It also overlaps with the Serratus, which in turn overlaps with the Obliques.

Back Torso

Primary Components:

• Trapezius
• Infraspinatus + Teres major & minor
• Latissimus Dorsi
• Obliques
• Glutes

The back is composed primarily of Two Very Big muscles: the Trapezius and the Lats. Because of this, the back tends to change its shape a lot, based on the position of the arms. Make sure to use references when doing back angles.

The Trapezius along with the deltoids act together as the primary actors in moving the arms, therefore their shape changes based on the arm position.

The Latissimus Dorsi is the biggest muscle of the back, and is often the most impressive. The upper part of the muscle has a higher density of muscle fibers, therefore it tends to bulk up a lot more compared to the lower part.

Arm

Refer to the Arm Anatomy Lesson for more detailed information.

Primary Components:

• Deltoids
• Triceps
• Biceps
• Coracobrachialis
• Brachialis
• Brachioradialis
• Forearm group
• Hand

The arms, by far, are the most active and nimble part of the human body. It has the ability to spin around, bend, rotate, etc. beyond what other parts of the body are capable of.

The deltoids are responsible for lifting the upper arm (with the forearms in tow). It’s composed of 3 parts, the front, middle, and back heads. Flexing different parts of the deltoids moves the arm in different ways.

The biceps and triceps pair is responsible for bending the arm at the elbow. While the biceps are the more popular of the two, the triceps is actually the bigger muscle of the two, and should not be neglected when drawing the arm.

The brachioradialis (sometimes known as the jerk-off muscle) is responsible for rotating the hand on the thumb-pinky axis. It’s a relatively prominent muscle that is commonly seen on muscular people.

The elbow bone is in fact one end of the Ulna, one of the two forearm bones.

The forearm group of muscles are formed of many small muscles, mainly responsible for the movement of the hands and fingers.

Legs

Thigh (Upper Leg) Components:

• Glutes
• Quadriceps
• Inner Thigh Group (hip adductors)
• Sartorius band
• Hamstring
• Tensor Fascia Latae
• Iliotibial Band

Refer to the Thigh Anatomy Lesson for more detailed information.

The Quadriceps are the stars of the thigh. The visible part of it consists of the vastus medialis (inner head), vastus lateralis (outer/side head), and the rectus femoris (middle portion).

The vastus medialis muscle is positioned slightly lower than the vastus lateralis muscle.

The rectus femoris is formed of two tube-like shapes, which is why it sometimes has a line in the middle.

The inner thigh group is often neglected by artists, but it usually makes up about 20-35% of the visible thigh from a standard front angle, and more when the foot is rotated outwards (such as in a sitting position).

Calf (Lower leg) Components:

• Gastrocnemius
• Soleus
• Achilles Tendon
• Tibia (shin bone)
• Shin muscle group
• Foot

The Gastrocnemius is the biggest muscle of the calf, but because it’s located in the back, it’s not always the most prominent. The soleus muscle is positioned under the gastrocnemius. Both muscles converge into the Achilles tendon, which connects to the heel of the foot.

The shin bone extends from the knee to the inner side of the ankle. The front face of the bone is not covered by any muscle, and can be felt with your hands.

The shin muscle group is a group of small muscles responsible for pulling the foot up, as well as the movement of toes.

Unlike the hands, the foot does not command much control over the legs. On the contrary, the foot’s position and rotation is often defined by the position and rotation of the legs as a whole, plus the surface on which it is resting.

Final Note

To master anatomy, you must first start by knowing what muscles exist, where they are, and what they do. You don't have to memorize the names of every single muscle, but being aware of them will already make a world of difference.

---

As always, if you have any questions, feel free to hit me up in the Art Labs channels in the AA Labs discord!