"Unfortunately, the knee's mechanics are better suited to chasing animals for dinner than to sliding into second base", says Stephen Messier, professor of health and exercise science at Wake Forest University in Winston-Salem, North Carolina. "We weren't designed to do the things we do with our bodies nowadays," he explains. "The knee's engineering isn't the greatest." (1)   Acting as cushions between these incongruent bones that make up the knee joint are meniscal discs that separate and lubricate them, and then it's wrapped up by a synovial joint capsule.  Everything slips and slides as it should, kind of.     

 

The knee joint is held together by four strong ligaments, like straps, on the back of the knee and at the patella, and two on the sides of the knee. These straps literally hold the knee together keeping it stable.  There is no elastic tissue in these ligaments and they do not stretch without consequences.  If stretched, they become permanently loose and ineffective in stabilizing the knee.  (As a comparison, some ligaments can be stretched up to 25 to 30% and up to 200% in the cervical spine.)     

 

Our femur, the thigh bone, is angled with respect to the vertical line of the lower leg.  The movement and action of the hip directly affect the knee.  Of the 11 muscles that cross the knee, 7 also cross the hip joint (3 hamstring and 4 quadriceps).  The load on the knee when the foot strikes the ground when walking is 4 times the body weight and 8 times when running.  Done to excess, the cartilage of the knee can become irritated and can possibly lead to arthritis and/or bursitis in or around the joint.   

 

Most importantly for us yogis is to remember that the knee is a hinge joint. Any other movement laterally or rotation around any axis risks damage to the ligaments and/or menisci.  In yoga, a misalignment of the knee is especially risky in weight bearing poses, like the Warriors, chair pose and side angle pose. 

In contrast, proper exercise can actually help protect the knee, whether you're with a trainer at the gym or in a yoga studio.  Strong muscles in the legs can help support the structure of the knee and many find their yoga practice has literally "cured" their knee problems.  

 

It's helpful to remember that there is really no "good" knee pain. So, be kind to your knees.  However you're sitting, and I guess you're sitting, give them a sweet, loving rub.

 

(1) http://www.yogajournal.com/health/1161

Reference:  Robin, Mel.  A Physiological Handbook for Teachers of Yogasana

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