Preparing for Sirsasana

The idea behind headstand is to maintain the inversion without exerting pressure on the top of your head or your neck, because that can cause serious unwanted injuries. If you’re apprehensive about getting into sirsasana, the main muscles to focus on are your shoulder muscles. Your anterior and posterior deltoids, your deeper trapezius muscles and other upper neck muscles, as well as your triceps brachii. In headstand, you require the strength of your shoulders and upper arms in order to support the rest of the body in the air, without injuring your neck.
A few good exercises that strengthen the shoulders involve dolphin pose. Dolphin pose is similar to downward-facing dog, except with your head and forearms on the mat, as if you were getting ready to kick up into headstand. From here, you can pulse and lift your head off and on the mat, using your shoulder girdle to push the head up. If this is a comfortable exercise, you can work on dolphin pushups, where you push forward into a forearm plank from dolphin pose (see attached picture). Even holding an active dolphin pose works to strengthen the shoulders and forearms. All of these exercises are necessary preparation to make sure your shoulders are ready to bear the weight of the rest of your body. Good luck with those sirsasanas!