JOINTS A joint is the juncture where two bones meet. Some joints can only move in one plane of motion, while others can move in all three. Te range of motion of a joint is the distance it is capable of moving along the direction of its plane(s) of motion. Te types
of joints most relevant to snowboarding are hinge, ball-and-socket, and gliding joints. ■ A hinge joint flexes and extends in a single plane. For example, the elbow is a hinge joint. Te knee is a modified hinge joint; it also glides and permits a minimal amount of rotation.
■ Like a joystick, a ball-and-socket joint has the ability to move in all three planes, giving it a broad range of motion. It can flex and extend in all planes, as well as rotate around an indefinite number of axes. Te shoulder and hip are examples of ball-and-socket joints.
■ With a gliding joint, the bones glide (slide) along their smooth surfaces in a limited amount of movement, with components of roll as well as glide. Te wrist and foot are gliding joints.
Te joints move in specific ways within their plane(s) of motion. With flexion, the angle between two body parts decreases, as when you flex your elbow to move your right hand toward your right shoulder. In extension, the angle between two body parts increases, as when you extend your knee to straighten your leg. With joint abduction, a limb moves away from the midline of the body, as when you lift and move your leg to the side. In adduction, a limb moves toward the midline of the body, as when you bring your knees together. Rotation occurs in a joint when a part of the body turns in the horizontal plane, as when you rotate your femur in your hip socket to turn your leg inward or outward. Circumduction, a complex movement that involves flexion, extension, and adduction, allows the moving body to trace an imaginary circle. Doing “windmills” with your arms involves circumduction of the shoulder joint.
HIP JOINT
Te hip is a ball-and-socket joint con- sisting of the side (socket) of the pelvis and the head (ball) of the femur. Te femur moves at the hip joint in all three planes, similar to a computer joystick. Technically, the femur rotates, abducts, adducts, and flexes and extends in the hip joint.
Even with this freedom of motion, the hip has limitations. When the femur abducts (moves away from the centerline of the body) the greater trochanter (that bone that is felt on the outside of the hips) impedes the hip’s range of motion when it contacts the pelvis.
Figure 4.3: Hip joint
60 AASI SNOWBOARD TECHNICAL MANUAL
TheSnowPros.org
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