Your knee primarily moves in one direction, which is the sagittal plane that involves movement in a front and back pattern. Its range of motion is determined by the range of motion of your connective tissues, muscles, tendons and ligaments that attach your upper leg to your lower leg. If any one of these organs is stiff or injured, then you would not have full range of motion in your leg, according to physiologist Susan Hall, author of "Basic Biomechanics."
Your knee joint is made up of the patella, or kneecap; the articulations at the ends of the femur and tibia, ligaments that hold the bones together; and tendons that attach the bones to the leg muscles. The knee is bathed in synovial fluid and has cartilages that provide smooth gliding of the bones, according to Hall. It has numerous bursae that provide cushion between the ligaments and bones.
Your knee moves through flexion and extension, with slight movement in internal and external rotation, according to Hall. Normal flexion of the knee, which is decreasing the angle of the knee, is between 120 to 150 degrees, while normal extension is between 5 to 10 degrees. Normal internal rotation is between 9 to 10 degrees, while external rotation is between 30 to 40 degrees.
The amount of mobility you have in your hip and ankle joints determines the risk of injury in your knee, according to physical therapist Gray Cook, author of "Movement." If your ankle or hips are stiff and lack full range of motion, then your knee has to compensate when you move. This is the primary reason for most knee injuries and knee pain from non-contact injuries. For example, if your hip is not able to turn when you change direction while running, then your knee has to turn to compensate, which is not its primary function.
If you wish to strengthen and increase the range of motion in your knee, you should first increase ankle and hip mobility before addressing the knee, Cook suggests. Once you have done so, perform strength exercises to increase ankle, knee and hip stability, such as squats, dead lifts, step-ups and lunges.
- Basic Biomechanics; Susan Hall
- Movement; Gray Cook
- Jupiterimages/Comstock/Getty Images
This article reflects the views of the writer and does not necessarily reflect the views of Jillian Michaels or JillianMichaels.com.