: Instead of a linear transition from "thin" to "buff," you could add a breakdown pose in the middle. This ensures that at 50% muscle, the character looks like a realistic athlete rather than just a blurry blend of the two extremes.
Are you building this for a (like Unity or Unreal) or as a modding tool for an existing title? How to Animate a MORPH - 2D Animation Tutorial
A feature for —which sounds like a character creation or animation utility for game mods (e.g., The Sims , Skyrim , or Fallout )—could be a "Proportional Mass Distributor" .
This feature would allow you to adjust one morph slider (like "Height" or "Muscle") while the software automatically and realistically adjusts surrounding body parts (like shoulder width or leg thickness) to maintain a natural human silhouette. Suggested Key Capabilities