Creating tension in the Fascia Cruis is a key component to perform a correct ELDOA L5-S1. Below is a paragraph from an anatomy and physiology book citing the crual muscles-
“Muscles Acting on the Foot… The fleshy mass of the leg proper (below the knee) is formed by a group of crural muscles, which act on the foot (fig. 10.35; table 10.19). These muscles are tightly bound together by deep fasciae, which compress them and aid in the return of blood from the legs. The fasciae separate the crural muscles into anterior, lateral, and posterior compartments, each with its own nerve and blood supply.