September 13, 2010, 02:16PM PT in Exam Preparation Blog |
As the world turns...so does your body
And just like the world, the body turns on an axis of rotation. But unlike the earth, the body has multiple axes of rotation options. And closely linked with the axis of rotation are planes of motion. Before you can understand the axis of rotation you need to review which planes of motion exist and how they divide the body. Below are the relevant manual pages:
ACE’s Essentials of Exercise Science: pg 110
Group Fitness Instructor 2nd edition: pg 34
Don’t forget the Exam Prep blog post on planes of motion!
(Going forward I'll assume you're familiar with planes of motion.)
So how does axis of rotation relate to planes of motion? Well, they work together! The axis of rotation is the imaginary line or point about which the lever rotates. The axis of rotation intersects the center of the joint and is perpendicular to the plane of movement. And if you just went…huh?, then check out the graphic examples of these movements - page 18(Essentials…) or pg 53 (Group Fitness Instructor) for the images - and think about the movement directionally. We’ll use the hip joint as our example.
The medio-lateral axis refers to the axis of rotation running towards the midline (medial) and away from the midline (lateral). Visualize a rod that goes through your hip joint from left to right (lateral to medial). The only action you hip can now make is flexion and extension (as the hip joint moves around the rod). Flexion and extension only occur in the sagittal plane. Therefore, flexion/extension occurs about the medio-lateral axis in the sagittal plane.
Anteriorposterior axis of rotation refers to the axis running from front to back (remember…anterior/front to posterior/back) Visualize a rod that goes in the front of your hip joint and sticks out the back. The only action your hip joint can now make is abduction and adduction. Abduction/Adduction only occurs in the frontal plane. Therefore, abduction/adduction occurs about the anterioposterior axis in the frontal plane.
Finally, the longitudinal axis of rotation follows the long line of the body. Picture a rod that goes in the top of your shoulder, down through your hip bone, and out the bottom of your foot. The only hip action you can make is internal and external rotation of the hip. Rotation only occurs in the transverse plane. Therefore, internal and external rotation occurs about a longitudinal axis in the transverse plane.
Just like with planes of motion, you may improve your comprehension of the material by getting up and doing the movements yourself while comparing with the manual images. Don’t be bashful - you can always tell people it’s an ACE recommended part of your studying technique!
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