Hyperextension of the knees messes with our posture. Our bones hold us up and our muscles move us. The bones of the body are meant to stack one on top of the other in order for weight to transfer successfully through the joints from the head to the feet. All of the bones need to be aligned properly for the body to work as designed. One of the classic trouble spots is the juncture where the shin meets the foot.
Hyperextension is the movement of a joint past its normal range of motion. In the case of the knees this means that the shin bones are pulled backwards into an obtuse angle with the foot. The body is designed for the shin to be at a right angle to the foot. If weight is going to move down through the spine to the pelvis and down the legs into the feet, the femur bone of the thigh needs to be situated directly on top of fibula and tibia of the shin so that the shin can be directly on top of the foot.
If the knee joint hyperextends it puts a great deal of strain on the ligaments at the back of the knee and the boney relationship of the shin and foot is thrown out of balance. It also affect the muscles above and below the knee joint—the hamstrings, the calves and everything else in the area.
I have spent a good deal of time looking at the picture above, which I came across randomly on facebook. I am assuming that it is a bikram yoga class as they encourage hyperextension of the knees for some ungodly reason. It wasn’t put up as an example of bad alignment. Quite the opposite, it was a celebration of this variation on natarajasana, dancers pose.  All I see is a bunch of knee capsules that are being put to a fairly severe test with one exception—there is a guy in the background in dark red shorts who seems to be standing correctly.
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