Leg Action in a Squat

The squat is a complex movement involving many actions in legs, or more specifically the knees and ankles. The muscles that control the actions of the knees are the front thigh, inner thigh and rear thigh muscles. Those that control the actions of the ankles are the calf muscles and the shin muscles. Learning the exact muscles that are at work during the squat and which specific action they control will allow you to better execute the squat so you can reap the maximum benefits of this complex exercise.

  1. Knee Flexion

    • To do the squat, you first place a barbell over your upper back and you stand with your body upright and feet a little wider than shoulder-width apart. Then, with your back as flat as possible, you lower your hips until your thighs are parallel to the ground. The first action of your legs during this downward phase is called knee flexion, or the bending of your knees. A four-parted muscle group known as the hamstrings is responsible for this knee action. These muscles, the semitendinosus, semimembranosus, biceps femoris long head and short head, pull on the lower leg bones, the tibia and fibula, to allow you to bend your knees.

    Ankle Dorsiflexion

    • In addition to knee flexion, you are performing ankle dorsiflexion during the downward phase of the squat. Dorsiflexion is basically the bending of your ankles. The tibialis anterior, fibularis tertius, extensor digitorum longus and extensor hallucis longus are the muscles that allow for this action. These muscles pull on your lower leg bones so you can bend your ankles as you lower yourself during the squat.

    Knee Extension

    • When you reach the parallel thigh position, you must then rise back to the upright starting position of the squat. The knee movement that occurs during this upward phase is called knee extension, or the straightening of your knees. A four-parted muscle group known as the quadriceps allows you to do this. These four muscles are the vastus medialis, vastus lateralis, vastus intermedius and rectus femoris. The quadriceps pull on the patella, or knee cap, to extend your tibia, or shinbone, so you can straighten your knees during the upward phase.

    Ankle Plantarflexion

    • Along with knee extension, you perform a movement known as ankle plantarflexion. This is the extension of your ankles. A total of nine muscles allow you to do plantarflexion. These muscles, the gastrocnemius lateral head and medial head, soleus, plantaris, tibialis posterior, flexor digitorum longus, flexor hallucis longus, fibularis longus and fibularis brevis all pull on the back of the ankle to extend it. And, as a result, you are able to straighten your lower legs as you ascend during the squat.