Sit on a leg extension machine. Select the appropriate resistance in the weight stack. Place your legs under the pad with your toes slightly in. The pad should rest on your ankles with your knees at 90º, if it's not, adjust the machine to get it. Contract your pelvic floor and core while keeping your chest up. Grab the hand bars firmly.
With your quadriceps, fully extend your knees while you exhale. Hold 1 sec. Return to the starting position with a smooth movement, preventing moving weights from touching the rest of the stack.TIPS: Try to not reach the end of the range of motion in each repetition.