(Not pictured: Place barbell on the rack so that its just below your shoulder height when standing next to it. Add desired weight plates and safety clips to each end. With your back to the squat rack, place shoulders underneath barbell and hands on barbell, then straighten legs to lift barbell off rack. Take a small step forward so barbell is away from squat rack.) Place one foot forward and the other foot back so that you have a wide stance between your feet, with toes pointing forward, abs engaged, and back straight.
INHALE: Bend at both knees to lower your body straight down towards the ground, but without exceeding 90-degree bends at the knees.
EXHALE: Straighten the legs to push back up to the start position to complete one rep.
Make sure your knees do not lock or move in front of the toes. Do not lean forward over your front leg--keep body upright. When lifting heavy weights, use a spotter for safety. Do not perform this exercise on a "Smith machine," because it can compromise your normal movement pattern, increasing injury risk.
Muscles Worked: Legs (quads, hamstrings, calves) and glutes