strong as a horse
(as) strong as a horse
Very physically fit; having great physical strength and endurance. Our father was always as strong as a horse, so it took us all by surprise when he was hospitalized by a heart attack at the age of 48. She got into weight lifting a couple years ago and is strong as a horse now!
*strong as a horseand *strong as an ox; *strong as a lion
Cliché [of a living creature] very strong. (*Also: as ~.) Jill: My car broke down; it's sitting out on the street. Jane: Get Linda to help you push it; she's as strong as a horse. The athlete was strong as an ox; he could lift his own weight with just one hand. The football player was strong as a lion.