The squat is regarded as a compound exercise because it requires movement around more than one joint. Focus tends to be on action at the hips and knees, but as you come up out of the squat, your ankle joints are performing plantar flexion. This means that not only does the exercise develop the muscles in the hips and thighs, but in muscles located in your lower leg as well.
Ankle Plantar Flexion
The ankle is formed by the tibia and fibula bones in your lower leg and the talus bone in your foot. It’s a hinge joint, which means it is only able to flex and extend, or move up and down. Ankle plantar flexion is when your ankle joint extends, meaning the top of your foot moves away from your lower leg. When you perform calf raises by pushing off the balls of your feet to lift your heels off the floor, you’re ankles are performing plantar flexion. Normal plantar flexion range of motion is zero to 50 degrees.
When you’re lowering down into a squat, while your feet remain fully on the floor, your tibia and fibula bones are moving forward. This forces your ankle into a dorsal flexed position. As you extend your hips and knees to rise up out of the squat, your ankles plantar flex to push the lower leg bones back to a vertical position.
Ankle plantar flexion is handled by two major muscles in the calves: the gastrocnemius and soleus. The gastrocnemius is large and located closer to the skin than the soleus. When your knees are straight, your gastrocnemius is in a more efficient position to perform ankle plantar flexion. When your knees are bent, it’s your soleus that takes the primary role. According to ExRx.net, because your knees are bent as you’re lowered in the squat, the muscle that is primarily responsible for plantar flexing is the soleus.
If you have difficulty squatting to where your thighs are parallel to the floor, it could be due to your ankle joints being too tight. According to certified strength and conditioning specialist Tony Gentilcore of T-Nation.com, in order to be able to do a full squat, your ankle joints need to be able to flex to about 15 degrees of dorsiflexion. If they can’t, your center of gravity may shift forward, placing excess stress on your knee joints. As a result, you’ll be performing a lesser degree of plantar flexion. Incorporate regular bouts of calf stretches if you find your ankles too tight.
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