Weight training free weight - Squat

This is example of exercise #4 Squat with  the instructions how doing this exercise: If the bar is racked, place the bar on the fleshy part of your upper back and grasp the bar at shoulder width. Keeping your back straight and head level, remove the bar from the rack and take a step back. Stand with feet slightly more than shoulder-width apart and toes pointed slightly outward.  (a)  Rest the bar on the back of your shoulders, holding it there with palms facing forward.  (b)  Keeping your head level and lower back straight and pelvis back, squat down until your thighs are below parallel with the floor. Let your thighs move laterally (outward) so that you “squat between your legs.” This will help keep your back straight and keep your heels on the floor. Drive upward toward the starting position, hinging at the hips and keeping your back in a fixed position throughout the exercise. The muscles of developed which is the Quadriceps,  gluteus maximus, hamstrings and gastrocnemius.