Bikram Yoga SLC instructor Mike Schenk
A common mistake in Standing Bow Pulling Pose is rushing to get into the fullest expression of the posture. If you can do the posture with your best form and alignment; depth will come with time. Bikram says, “Take the time to get yourself firmly grounded and set on your standing leg before you bring your body forward and down. When you begin to move, take your time and stay in control. The most important advice I can give you here is don’t be in a hurry to dive into this position.”
The standing leg is your foundation. Keep the knee locked with a firm contraction of thigh. If you don't feel that you have the balance to go forward yet, stay in this position until you have a firm foundation.
Once you begin kicking against your hand, your knee should go straight back, your hips should stay level. The arcing of the spine, keeping balance, and holding the knee and hips in the right alignment should be your main focus before you begin to lower your upper body. All of this is difficult to do if you aren't concentrating on each element as you move slowly into the posture.
Even advanced students should, from time to time, slow it way down. Make sure that you can stop the posture at any moment and hold it still, move a millimeter more, then more, until the final posture is inevitable.