Etymology and origins
The name Vajrasana denotes a medieval meditation seat, but its usage varied. The 15th century Hatha Yoga Pradipika called it a synonym of Siddhasana, where one of the heels presses the root of the penis; according to Yoga-Mimamsa III.2 p.135, this explains the reference to vajra, a weapon. The 17th century Gheranda Samhita 2.12 describes what Light on Yoga calls Virasana, with the feet beside the buttocks, while in other texts Vajrasana appears to mean the modern kneeling-down position, with the buttocks resting on the feet. The yoga scholar Norman Sjoman notes that Light on Yoga is unclear here, as its account of Laghuvajrasana has the knees and feet together, but it does not describe the basic Vajrasana.
The practitioner sits on the heels with the calves beneath the thighs. There is a four finger gap between the kneecaps, and the first toe of both the feet touch each other and sit erect.
The reclining form of the pose is Supta Vajrasana.
Some orthopaedic surgeons claim Vajrasana may be harmful to knees. It has also been linked to damage to the common fibular nerve resulting in foot drop, where dorsiflexion of the foot is compromised and the foot drags (the toe points) during walking; and in sensory loss to the surface of the foot and portions of the anterior, lower-lateral leg. In this context it has been called "yoga foot drop".
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Many yoga gurus had suffered knee and joint problems from performing the 'vajrasana' posture [...]
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