Feet are together as the torso and head bend forward toward the legs. Don't: Hyperextend the knees. That puts pressure on the hamstrings (the muscles at the back of the thigh) and the Achilles tendon. There's a connection from the Achilles all the way up to the spine, so hypertextending almost puts a lock on the energy flow. This can lead to more tightness in the lower back and strain on the knee joints.
Glenn Koenig / Los Angeles Times
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