Sentence:  And they could n't have entrusted Henri to better hands because `` le professeur '' knows his muscles from the sterno-cleido mastoideus of the neck right down to the tibialis anticus of the leg - and better still , he knows just what <WSD>exercises</WSD> work best for them and what Weider principles to combine them with for fast , fast muscle growth . 
Meaning of the word marked with <WSD> tags:  the activity of exerting your muscles in various ways to keep fit