Just a quick question, is elastic energy stored in the tendons OR the muscles? Thanks for looking.
Both. The sheath surrounding muscle tissue stores elastic energy as well.
"The traditional view of tendons serving to attach muscle to bone presents only part of the picture. Tendons, together with other series elastic components, particularly after termination of powerful isometric or eccentric contractions, play a vital role in storing elastic energy during locomotion and other motor acts, thereby serving energy and increasing muscular efficiency."
So... yeah, what Dan said.