You do not sculpt muscles. You sculpt light bounces off. You sculpt transitions between hard bone and soft tendon. You sculpt silhouettes that read as "hero" or "grandmother."
Understanding how muscles stretch and contract allows you to depict tension, balance, and the "line of action". anatomy for sculptors.pdf
The book standardizes a specific visual workflow for every body part, moving from the inside out. You do not sculpt muscles
Your chisels, styluses, and clay will thank you. and clay will thank you.