After your hands are together above your head, raise your lead leg by flexing at the hip and knee. At the same time, bring your hands from above your head, back to your chest. The windup phase ends when the front leg is at its maximum height and the two hands begin to separate.
Downward rotation of both scapulas using the pectoralis minor and rhomboid muscles.
Extend shoulder joint by eccentrically contracting your latissimus dorsi, teres major, lower pectoralis, and posterior deltoid muscles.
Flexed about 30˚ by concentrically contracting both heads of thebiceps brachii, brachialis, and brachioradialis muscles.
With your step leg, your hip is flexed by concentrically contracting your iliacus, psoas major and minor, rectus femoris, sartorius, pectineus, and tensor fasciae latae muscles, causing an anterior pelvic tilt. The opposite of your hip externally rotates by eccentrically contracting your piriformis, gemellus superior and inferior, obturator internus and externus, and quadratus femoris muscles. This causes a left transverse rotation.
Step foot knee is flexed to 90˚ by concetrically contracting your biceps femoris, popliteus, semimembranosus and semitendinosus. The opposite knee externally rotates by isometrically contracting your biceps femoris muscle.