How to Use ZBrush to Sculpt & Animate Anatomically-Accurate Muscles

Introduction

Hey everyone! My name is Sherif, I'm an Environment Artist. Recently, I've started experimenting with character art and anatomy for fun.

I've been sculpting in ZBrush for a few years, mostly working on organic environment assets like trees and rocks, but over the past couple of years, I thought I'd try doing something different. At that time, anatomy came into my life, and it seemed fun and challenging.

Speaking of the anatomy studies series, I wanted to develop a deeper understanding of human anatomy, and I thought these kinds of studies would help me do that. If you're only sculpting a model in a single pose, you might be able to get away with some anatomical inaccuracies here and there. However, when you start animating the model, it forces you to do more research and hopefully learn more in the process.

References

It goes without saying that having good references to work with is crucial. But, of course, if you're sculpting a specific pose, you might not be able to find shots from every angle, unless you have a 3D scan or something similar to work from.

In this case, I align the base mesh/blockout to the main reference, and then I try to sculpt the rest of the figure in a way that makes anatomical sense. If I'm unsure about specific body parts, I look for references online. Googling phrases like "forearm pronation" or "triceps extension", for instance, would give me a rough idea of how it should look.

Additionally, I often search for bodybuilding or stretching tutorials on YouTube that focus on the muscle or body part I'm working on. This helps me gain a better understanding of how the joints, muscles, and bones work, as well as their range of motion. Knowing these details is essential for sculpting or painting them accurately.

The Triceps Animation

I started from the base mesh I made earlier, here's a quick time-lapse for that.

My workflow is very straightforward. I collect some references, start with a simple blockout of the main forms of the torso, and then continue refining as needed.

Here's the timelapse for the full process:

Basically, after sculpting the main pose, I add a new layer, move the character around, and refine the new pose. For the triceps animation, I use two layers in addition to the main pose.

The number of layers required for the animation depends on the specific movement. I have found that more linear motion, such as movements that don't involve much rotation (like the torso animation I did earlier), can be achieved using just one layer. However, if the movement involves a lot of rotation, such as flexing or extending an arm, it is necessary to split the movement into multiple layers to guide the motion. After all, layers are a form of displacement that stores initial vertex positions and allows you to switch back to them later. This works well for simple movements, but creating more complex movements with lots of rotation requires careful planning. You would need to create intermediate poses and plan how these poses should look before sculpting.

Here is an example of what the setup looks like in ZBrush:

You can also use the timeline feature in ZBrush to record the animation, it lets you set the layers as keyframes, even though it's not the most intuitive tool to use.

Here is a good tutorial that shows how to use it:

Rendering & Lighting

I tried to keep everything inside of ZBrush for the sake of simplicity. Exporting and rendering over 30 million animated meshes in Maya or Blender would have taken longer than I'd like. Also, I thought this would be a good challenge to try and get decent-looking renders in ZBrush. Below, you can see my usual setup for rendering these studies.

Speaking of render settings, I also use Preview Shadows and Ambient Occlusion to add some extra details. There isn't a specific approach for this, I simply adjust the settings until it achieves the desired look. Additionally, I enable Preview Wax/SSS, as it helps create a more natural appearance for the skin.

I'm using a double-shaded material. The first channel consists of the default basic material with added subtle noise and adjustments to the specular colors, intensity, and curve. The second channel is for adding the finer specular highlights.

My setup for the lighting is very simple, just the main light and the fill light, both with the default settings. Sometimes I change the light intensity curve. However, it's not needed for most renders.

Final Words and Pieces of Advice

The triceps animation didn't take long, around 10 hours or so. However, I started from the base mesh I sculpted earlier. Recently, I've been trying to set a personal project time limit of around 20 hours. Otherwise, I could spend weeks on the same piece and never actually finish it.

The main challenge for this series was finding useful references to work with, and even then, there was still a lot of guesswork involved since the references wouldn't cover the specific movement you're sculpting from all angles. That's a good thing though, since it forces you to develop a more thorough understanding of anatomy, the forms, and the range of motion of the muscles.

Try to get daily practice, even if it's just one or two hours a day. Making this a daily habit really helped me learn faster. Also, be sure to post WIP shots for feedback on art-related forums. For example, I got some great anatomy feedback from users on Reddit. Sometimes, when you stare at a sculpture for too long, you might overlook obvious issues with it. Getting another person to evaluate it is always a good idea, especially when it comes to spotting anatomical issues.

Thanks for reading my interview and I hope you found this helpful!

Sherif A. Dawoud, Senior 3D Artist

Interview conducted by Theodore McKenzie