Parivrtta = revolved
parsva = side
kona = angle
This seemingly easy pose is very difficult to perfect in alignment. The important part of this pose is to twist the upper body from the thoracic spine and not the lumbar spine. Some benefits of this pose include better balance, digestion, and stretches many parts of the body including the hamstrings, spine, chest and shoulders.
When in this pose, the spine is in axial rotation. In the upper body, the scapular is in downward rotation and shoulders are internally rotated to hook the elbow outside the knee. In the lower body, the hips and knees are in flexion in the front leg, while the hips and knees are in extension in the back leg.
The key muscles worked to rotate the spine towards the front leg are the erector spinae, internal obliques, transversospinalis and external obliques. In the upper body, the trapezius, pectoralis major and minor, serratus anterior and coracobrachialis works to lengthen the spine in this pose. The muscles worked in the lower limbs to hold the front leg in 90 degree angle, extend the back leg, and find balance in this pose include the adductors longus, magnus and brevis, gluteus maximus and medius, hamstrings and piriformis.