This project is a muscle rig I made back in 2016 during my time at university to see how I could apply bone constraints to emulate the flexing and stretching of muscles under the skin. The system is made up of a Skeletal Rig and a Muscle Rig. The Skeletal Rig acts as the anatomical bones, moving rigidly akin to a standard mechanical rig. Attached to this is the Muscle Rig, mimicking the way muscles attach to the bones of a person.

Where it differs from reality is the hierarchy of motion. In a human body, muscles drive the skeleton, but because a rig puppets our mesh, the Skeletal Rig instead drives the Muscle Rig. The Muscle Rig is set up to respond to the skeletal motion and uses stretching constraints to enable the muscle armatures to change size. This scaling happens along the direction of the muscle fibers to mimic the way real muscles stretch and contract. The Muscle Rig is then weighted to a series of muscle meshes that deform along with it.

Finally, the skin is applied over the entire assembly. It is weighted to the Skeletal Rig and shrink-wrapped to the muscle geometry. This shrink-wrapping allows the skin to slide over the muscles while maintaining its general position on the arm. The Skeletal Rig must apply its motion first in the modifier hierarchy; otherwise, the skin will slip and slide unnaturally during animation.

This workflow was a completely experimental method I developed based on my rigging experience with bone deformation and constraints. While it may not be the standard for all contexts, it represents the foundational logic used in complex rigs at studios like ILM or Weta when creating CGI creatures. By combining this method with soft body simulation and accurate anatomy, you can achieve very realistic results. These principles are what drive more advanced systems in Houdini and other technical 3D packages and fundimentally all complex rigs are a layering of simpler rigs and simulations that colminate into the complex mind blowing motion you see on the big screen.

Next up a rig ive always wanted to tackle is that of a Transformer like the Michael Bay Films.