Strain at the leash
Be enthusiastic to free oneself from the restrictions that bar one's progress.
The allusion is, of course, to a dog held on a lead and straining to go faster. Sir Walter Scott was the first to use it in literature. He included the expression in The Talisman, 1825:
"King Richard looked... at the Nubian and his dog; but the former moved not, nor did the latter strain at the leash."
See also - phrases coined by Sir Walter Scott.