Understanding Torque: A Guide to Understanding Proper Movement through Physics
When we exercise, we’re using our joints to exert force and move without compromising our spine. To do this, we need to make sure we activate the ball-joint of the shoulder and hip joints, but if you don’t know how to do this you can easily injure yourself. Here comes the concept of rotational force: torque. Your shoulder and hip joints are ball shaped bones sitting inside an open socket. If we leave our joints loose during an exercise such as a push up (shoulder joint) or a squat (hips) the ball-joint is left free to slide around inside the socket, causing instability. To prevent this, you need to use rotational force to tighten the musculature inside the joint and create stabilization.
To envision this, imagine a hammer. For the sake of this visualization, imagine that the flat end of the hammer is our ball joint. Now, wrap a towel around the hammer. The towel represents our musculature inside the joint. Left loose, the hammer can slide around inside the towel, but if we twist the towel tight, it will stabilize the hammer. This is the same concept as your muscles stabilizing a joint when you make torque. To create torque in our arms, we rotate our elbows. To create torque in our hips, we rotate our knees.
However, the direction you rotate matters. In general, if your arms or legs are in front of your torso, you will create torque using external rotation. Basically, you will rotate your elbows or knees away from your body. For the legs, this would mean screwing your feet into the ground outward from your body. You don’t want to actually move your feet. Your feet should be parallel and facing forward for stability, but you should be screwing them into the ground to flex your knees outward and tighten your butt. Voila, stabilization.
With the arms, we create torque in the push-up position by keeping our hands parallel and screwing them into the ground just like we did with our feet. This will create torque in the elbow and rotate it back. If you rotate the opposite way, it will create instability in the joint.
Now, in the case of the knee, it will always create stability to rotate the knee outward and not inward. ACL injuries happen when the knee rotates inward in order to stabilize the hip, and it results in an unraveling effect. This is because of the structure of the knee. To demonstrate the structure of the ACL tendon in the knee, cross your middle finger over your index finger like the image below. Now wrap your fist around the two fingers with your other hand and twist. Notice that in one direction, it tightens your two fingers, but in the other, it unravels them. Inside the knee joint, your ACL is set up in a similar way.
The best way to avoid rotating your knees inward and damaging your acl is to keep your feet parallel and forward during exercises. Many people rotate their feet outwards to gain stability and mobility. The problem is that as you rotate your feet outward, your ability to make torque diminishes. To demonstrate this, try flexing your butt with your feet forward. Now try it with your feet horizontal, pointing towards opposite sides of the room.
As the feet move outward, you shorten your base and you collapse your arches.
In application, you should always keep your feet pointed forward when squatting or performing exercises, and from this position should be screwing your feet into the ground to create torque in the joint. When you use torque in the hands and feet, you naturally stabilize the rest of your body, and it makes it much easier to maintain a stable spine, which is our end goal.
For more information on torque and other movement information, I greatly recommend Dr. Kelly Starrett’s Masterpiece: How to Become a Supple Leopard. You can also check out his website at mobilitywod.com
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