An exercise performed on a machine in which the hamstring muscles are exerted to bend the knee while acting against resistance applied to the lower calf. The exercise may be performed while prone or standing, depending on the design of the machine
You'd never dream of doing just bench presses to build a massive chest, or only lateral raises to build up your shoulders, so you'll surely limit your overall leg development if you restrict your hamstring training to leg curls.
An exercise, usually performed lying on the stomach with weights, in which one lifts one or both heels towards the buttocks and then returns to the starting position, while the rest of the body is kept immobile