As my weight fills a leg the thigh muscle tightens and the hamstring slackens. The relaxed hamstring becomes a refuge for the mind, allowing energy to suddenly appear in the opposite region of the body. So, weight in left leg, mind in left hamstring, energy in the region around the right shoulder/ear. Castaneda said that one's personal history resides in the hamstrings, and that they must be worked to loosen the grip that history has on us.