ASANA
Crow Pose · Kakkasana / Crane Pose · Bakasana
Foundational Arm Balance
Most typically these poses are both referred to as Bakasana. Kakkasana(the arm bent version) is the foundational arm balance posture. In terms of strength it requires knowing how to stabilize the shoulder girdle while pouring the weight forward into the hands. The feeling is usually surprising for first timers as it's not as strenuous as it seems when done low to the ground with a considerable bend in the elbows and counter balancing your weight between the front and back.
To stabilize the shoulder you can try this exercise in table pose first. Position on the hands and knees with straight arms under your shoulders. Press the floor away with your chest, externally rotate the arm, move the shoulders back from your ears and create a slight action as if to slide the hands apart on the floor. This is the minimum but you could also add in internal rotation of the forearm to press the index knuckle down. Basically, try to co-activate as many muscles around the shoulder joint as possible to create stability.
To stabilize the shoulder you can try this exercise in table pose first. Position on the hands and knees with straight arms under your shoulders. Press the floor away with your chest, externally rotate the arm, move the shoulders back from your ears and create a slight action as if to slide the hands apart on the floor. This is the minimum but you could also add in internal rotation of the forearm to press the index knuckle down. Basically, try to co-activate as many muscles around the shoulder joint as possible to create stability.
Technique
Squat down lifting your heels as you place your hands in front of you. Fit your knees as high up your arms as possible. If you are closer to the shoulders, put your knees slightly outside your arms and hug in as you come into the pose. If your knees are closer to your elbow you could also try placing the knees on the back of the arms. Some people will easily get minor bruising on the arms.
Start to learn your weight forward and grip your fingers down. Hug the elbows in slightly and look to the front. Keep leaning until your feet feel very light. Keep using your fingers to control and keep your head up even as you lean forward. If you are scared of falling on the head you can place some cushions in front. Once you are far enough forward the feet will no longer be bearing any weight. Pick them up slightly and hug the big toes in together.
Start to learn your weight forward and grip your fingers down. Hug the elbows in slightly and look to the front. Keep leaning until your feet feel very light. Keep using your fingers to control and keep your head up even as you lean forward. If you are scared of falling on the head you can place some cushions in front. Once you are far enough forward the feet will no longer be bearing any weight. Pick them up slightly and hug the big toes in together.
With strong and flexiblee enough wrists, core, and shoulders a straight arm version of the pose can be done. From the Kakkasana press the arms straight and crunch the abdomen to lift high. It becomes especially more important to press into the front part of the palm(1st knuckles) to protect the wrist in this variation.