With Pincha Mayurasana starts the strength section of the Intermediate Series of Ashtanga Yoga. This first posture focuses on stabilizing of the shoulderblades (scapula).
In case of an existing shoulder injury, jumping out of the posture (vinyasa nine) may need to be modified.
Inhaling, hop forward, landing your knees next to your hands. Exhaling place your forearms on the floor. Ensure that your hands are close to the front of the mat to ensure that upon exiting the posture your feet will still land on the mat.
Make sure that your elbows are shoulder width apart and keep your forearms parallel throughout the performance of the Pincha Mayurasana. As beginners to the posture will have the tendency to place the elbows too far we suggest to initially check the stance in the same fashion as done in Shirshasana (headstand). Place your hands around the opposite elbows and make sure that your knuckles and fingers are outside of your elbows. Maintaining this precise distance between your elbows, now place your forearms parallel to each other and ground your hands down firmly, spreading your fingers. During the ensuing movement make sure that neither your wrists move towards each other, nor your elbows move further apart.
Straighten your legs now and, walking your feet in towards your elbows as close as possible, lift your hips high over your elbows in the process. The further you can walk in, the less momentum you will need to get up into the pose making it easier to fade out that momentum and come to a point of balance on your forearms.
Inhaling, lift your head and gaze towards a point between your fingertips. If you find it difficult to focus on a spot on your mat consider placing a small object in your chosen location or mark a spot on your mat. For those whose balance is unstable this will be a welcome aid. Fixing your gaze to a spot makes it much easier to establish your balance.
Proceed now to kick up into the full posture one leg at a time. Students with extremely long hamstring muscles may be able to perform the movement without momentum, viz while keeping the left foot on the floor, extending the right leg up and eventually over the head and then through a mere pivoting action, lift the second leg up bringing both legs together. In general this cannot be recommended. One usually needs to twist the pelvis too much to achieve this transition and especially when done always on the same side a muscular imbalance may result in pelvic obliquity.
It is therefore better to learn to kick up with straight legs, one leg after the other (scissor kick). Extend your straight right leg up into the air as high as possible without twisting your pelvis. Bend your left leg and, inhaling, push off the floor with your leg and raise the now straight left leg up until both legs meet.
If you don’t make it all the way up, lift your gaze slightly. The more you lift your gaze, the more you will extend your back and neck and subsequently the higher you will lift up. If you raise your gaze too much you may drop over into a backbend. In the beginning when learning the posture, the teacher should be present to spot the student and prevent the student from overshooting the mark. Within a short time the student will have stored the memory of how much force is needed to reach the exact position will be able to perform the movement without the help of the teacher.
It is also not advisable to use a wall for this purpose, as is the case with using a wall for headstand or handstand. With the safety of the wall to catch them student may not attempt and thereby learn to use only the amount of force necessary to reach the balance position. The wall is an inert, tamasic object and cannot give you feedback whether you are using too much force when kicking up. This way fine-tuning never occurs and one will become dependent on the wall like on a crutch. Students usually will become independent from the teacher from within a week to a month when learning this and similar postures. When employing a wall this independence often never occurs.
Once you have learned kicking up on one side, change sides and practice kicking the other leg up first. Even if you kick up with momentum rather than resorting to flexibility, the constant use of the same leg may lay the foundation for a muscular imbalance in the pelvis. Finding one side much harder than the other obviously points towards an already existing imbalance that needs to be rectified by giving preference to your weaker side.
Once you can kick up on both sides, you may practise swinging both legs up at the same time. To make this more accessible start by bending both legs during transit. Once that has become easy practise it keeping both legs straight and together in transit. This difficult movement, however, requires copious amounts of hamstring flexibility.
Once you are up in Pincha Mayurasana and have established your balance, engage your abdominal muscles to flatten out your low back. Straighten up, grow as tall as you can and fully open your chest and shoulders. This is of course possible only if the humeri (arm bones) can be flexed fully (arms above head position) using the deltoid and triceps muscles. Any residual stiffness in the shoulders needs to be removed first in Downward Dog and later through back bending before one is ready to attempt postures like the present one. This is the reason why any arm balances are practised only after proficiency in back bending is gained. Starting the practice of arm balances with shoulder joints that are not yet fully opened usually means that deep back bends cannot be reached anymore as any future back opening will be counteracted by the back firming effect of the arm balances. For this very reason the performance of postures like handstand etc. needs to be postponed until ones back bend is open enough to perform postures like Kapotasana and the like.
Once you have gained confidence, drop your gaze between your wrists and lower your head. The action of sucking your shoulder blades into your back will bring the serratus anterior and subscapularis muscles into play. Make sure that your elbows do not turn out and that your wrists do not move closer together. If this is the case you will need to more effectively engage your infraspinatus and teres minor muscles (often fused to one muscle). Infraspinatus externally rotates the humerus (arm bone) and is of course the antagonist to the internally rotating subscapularis. You will need to use infraspinatus concentrically (shortens during use) and subscapularis eccentrically (lengthens during use). In this way the subscapularis does not internally rotate but it’s origin sucks the medium borders of the scapulae (shoulder blades) into the back. This is an important detail for the stabilisation of the shoulder joint. Do not allow a winged appearance of the shoulder blades.
Take five slow breaths while looking down on the nose. On the last exhalation bend your hip joints by about 30 degrees. As you inhale strongly hook the breath into the bandhas and extend upwards, becoming as light as possible. At the peak of the inhalation, when you are most buoyant, flex both legs at the knee and then perform a kicking movement with both legs. This will reduce weight on your arms and since your hip joints are slightly flexed, the vector will not only go up but also slightly towards your elbows. Simultaneously execute a strong push with both hands as if pushing the floor away from you. Once your hands lift off, pull them out and place them further towards the foot end of your mat. The further down you can place them the softer your landing will be. Remember that this transition should not be performed with an existing shoulder injury. Especially a glenoid labrum tear is unlikely to heal if you perform rapid movements under load with your shoulders.
Exhaling, catch the weight of your body with your hands and lower down slowly keeping the legs straight and flexing the feet before landing in Chaturanga Dandasana. This whole transition is very challenging of course but important nevertheless. The key is coordination and timing. The key actions of kicking into the right direction, explosively pushing with ones hands and pulling the hands out need to be performed almost simultaneously at the peak of inhalation. There is a brief moment during the descent of the legs that one feels they no longer have control of the weight of their legs and gravity takes over. You must observe this moment and before your feet reach the floor, take the opportunity to move your hands and place them in their new position.
 Remember that raising your arms above your head is called flexing the humerus and that extending the humerus is defined as returning from flexion.
This is an excerpt from my 2009 text Ashtanga Yoga The Intermediate Series – Anatomy, Mythology and Practice