The Sanskrit word vajra means thunderbolt or diamond. The body is rigid as a diamond in this posture. This is a basic posture for many other asanas and meditation.
Position of Readiness
Sit with legs extended together, hands by the side of the body, palm resting on the ground, fingers of the hands together pointing forward.
Bend the right leg at the knee and place the foot under the right hip with sole remain inside. Now same way bend the left foot and place it under the left buttock. While sitting on the bent feet, do not sit on the heels the heels should remain out and toes inside with Soles upward. Keep hands resting on the respective thighs. Sit straight, gaze in front close the eyes. Breathe gently through your nostrils and sit in this position for at least three minutes. While returning to the original position, bend little towards right side take out your left leg and extend it. Similarly extend your right leg and return to the original position.
The Vajra-asana is a versatile posture well suited for meditation; rest in between other seated postures, or as an aid to digestion. This strengthens thigh muscles and calf muscles
The Vajra-asana can be held for as long as is comfortable it simply depends on the reason for doing the posture. Persons suffering from piles should not practice it.