Muscle was part of animals.
The Third Doctor used Houdini's trick of contracting the muscles to escape from the Eight Legs on Metebelis III. (TV: Planet of the Spiders) During his seventh incarnation, he tried to use the method again to get out of the Process's cocoon, but it was too tight. (PROSE: Cat's Cradle: Time's Crucible)
The Galapogans used the illegal muscle enhancing drug mediphosphide to help them win at the Intergalactic Trials. Their attempt to cheat was exposed by the Eleventh Doctor and the team were arrested and disqualified. (COMIC: The Intergalactic Trials)