The thunderbolt posture is one of the safest sitting postures for Yoga students with back problems. Vajrasana increases the flexibility of your ankles, knees, and thighs; improves circulation to the abdomen; and aids in digestion.
Use the following steps to practice this posture:
Kneel on the floor and sit back on your heels; position each heel under the buttocks on the same side, and rest your hands on the tops of your knees, with your elbows bent and your palms down.
Lengthen your spine by stretching your back in an upward motion, balance your head over your torso, and look straight ahead.
In the classic posture, which isn’t recommended for beginners, the chin rests on the upper chest, and the arms extend until the elbows are locked and the hands are on the knees.
If you have trouble sitting back on your heels because of tightness in your thigh muscles or pain in your knees, put a cushion or folded blanket between your thighs and calves. Increase the thickness of your lift until you can sit comfortably. If you feel discomfort in the fronts of your ankles, put a rolled towel or blanket underneath them.
The Sanskrit word vajra (pronounced vahj-rah) means “thunderbolt” or “adamantine.” So this posture is also known as the adamantine posture.