Hello! Welcome back to our series on arm anatomy.
In the last lesson, we focused on the deltoid, establishing it as a crucial transitional muscle that connects the torso to the arm. We saw how its three heads originate from the shoulder girdle and converge to insert about halfway down the humerus, wedging itself between the muscles of the upper arm.
Today, we'll move just below that insertion point to explore the two major muscle groups that define the bulk and contour of the upper arm: the biceps and the triceps. Our goal is to identify and draw the biceps and triceps and their effect on arm contour. You'll learn to see these not just as lumps on a cylinder, but as a functional, antagonistic pair that flexes and extends the arm, changing shape in predictable ways.
1. The Flexors: Biceps and Brachialis
The front of the upper arm is primarily defined by the biceps brachii, the famous muscle everyone flexes to show strength. However, sitting just beneath it is the brachialis, a muscle that is critical to the overall form of the arm.
To understand their relationship and individual forms, we'll turn to a video from Proko's anatomy course.
How to Draw Biceps - Upper Arm Anatomy for Artists
This video, 'How to Draw Biceps,' provides an artist-focused breakdown of the biceps and the underlying brachialis. We'll start with their basic structure and function.
Watch from 00:35 to 04:54. Pay close attention to: The relationship between the biceps and brachialis (the 'muscle sandwich' analogy). How the brachialis, though hidden, pushes the biceps out and contributes to the width of the arm, especially in a side view. The origin and insertion points of the biceps' two heads. Notice that the biceps does not attach to the humerus bone itself. The asymmetry of the biceps: the 'short head' is actually longer.
A key takeaway here is how these muscles work together. The brachialis is the workhorse for flexing the elbow, while the biceps, which attaches to the radius in the forearm, also helps in rotating the forearm (supination). This rotation has a dramatic effect on the biceps' shape.
Let's watch the next segment of the video to see this in action.
How to Draw Biceps - Upper Arm Anatomy for Artists
Now, let's see how forearm rotation changes the contour of the biceps. This is a crucial concept for drawing dynamic poses.
Watch from 04:54 to 05:34. Observe how the biceps flattens during pronation (palm down) and becomes shorter and fuller during supination (palm up). This is a direct result of its attachment point on the radius.
This interaction is what makes the arm feel alive. A flexed bicep with the palm facing up looks very different from a flexed bicep with the palm facing down.
2. The Extensors: Triceps Brachii
On the back of the arm, we have the triceps brachii. As its name implies, it's a three-headed muscle. It is the antagonist to the biceps/brachialis group and is responsible for straightening (extending) the arm. It is actually a larger muscle group than the biceps and contributes significantly to the arm's overall mass.
How to Draw Triceps - Arm Anatomy for Artists
Let's move to the back of the arm with Proko's 'How to Draw Triceps.' This video does an excellent job of simplifying this complex muscle group.
Watch from 00:21 to 05:42. Focus on these key artistic concepts: The 'Horseshoe' Shape: The three heads (long, lateral, and medial) wrap around a large, flat tendon. This creates a characteristic 'U' or 'horseshoe' shape that is a key landmark for artists. Asymmetry: Note that the bulk of the muscle mass is on the inner (medial) side of the arm, while the tendon is more visible on the outer (lateral) side. The Tendon: Pay attention to how much of the triceps' length is actually tendon. This flat area contrasts with the bulging muscle bellies around it. Forms: The lateral head is often drawn as an egg or comma shape, while the long head is a larger, teardrop form.
Understanding the interplay between the muscular heads and the central tendon is the key to drawing convincing triceps. The muscle isn't a single bulge; it's a collection of forms with a flat plane running through them.
3. Synthesis and Reference
Now that we've looked at the biceps and triceps groups separately, let's see how they fit together to form the complete upper arm.
For a quick textual summary, the article "Drawing Anatomy Arm" provides concise descriptions and diagrams that reinforce what we've learned from the videos. It's a great resource to bookmark for future reference.
Drawing Anatomy Arm｜Understand Bones, Muscles, and Motion
Let's quickly review the main points with this article.
Skim the sections on the 'Upper Arm (Biceps Group)', 'Biceps Brachii', and 'Triceps Brachii Group.' Notice how the diagrams simplify the forms and confirm their locations. You don't need to memorize every detail, just reinforce the main shapes and functions.
4. Practice: From Anatomy to Contour
Theory is essential, but practice is where understanding solidifies. Your exercise is to apply this knowledge by identifying and drawing these muscles from photo references. This will train your eye to see the underlying anatomy in real people.
Exercise: Drawing Biceps and Triceps (30 minutes)
- Find References: Search for three clear, well-lit photos of arms:
- An arm flexed (e.g., "bicep curl pose") to see the biceps at peak contraction.
- An arm from the back, flexed or extended (e.g., "tricep flex pose") to see the horseshoe shape.
- An arm in a neutral, relaxed pose from the side.
- Analyze and Trace (Layer 1 - Red):
- In Procreate, import a photo. On a new layer, trace the primary contours of the biceps, triceps, and brachialis. Don't just trace the outline of the arm; trace the shapes of the muscles themselves as you see them on the surface.
- Construct (Layer 2 - Blue):
- Hide your tracing layer. On a new layer, simplify the muscles you identified into basic forms, as described in the Proko videos (e.g., ovals for biceps, a horseshoe/teardrop and comma shape for the triceps). Focus on their placement and how they overlap.
- Draw (Layer 3 - Black):
- Lower the opacity of the photo and your construction layers. On a final layer, try to draw the arm's contours. Use your construction as a guide to place the bulges and transitions correctly. Focus on how the muscle forms create the final outline of the arm.
- Repeat: Do this for all three reference photos. The goal is not a perfect render, but to practice identifying anatomy and using it to construct a believable arm.
Conclusion
Great job! You've now dissected the two primary muscle groups of the upper arm. You've seen how their individual shapes, their relationship to each other, and their function directly influence the contours we see on the surface.
Key Takeaways:
- The front of the arm is defined by the biceps and the underlying brachialis, which work together to flex the elbow.
- The shape of the biceps changes significantly with forearm supination (fuller) and pronation (flatter).
- The back of the arm is defined by the three-headed triceps, which extends the arm. Its form is often simplified to a horseshoe shape created by the muscle heads wrapping around a large central tendon.
- Biceps and triceps are an antagonistic pair; when one contracts, the other lengthens.
In our next lesson, we will continue down the arm and tackle the major forearm muscle groups. This area can seem intimidating, but we will simplify it into manageable forms, just as we have with the upper arm.