The posture pictured to the right is called Short Man (or Short Person). It is normally done with the hands in prayer at the chest, but I have taken to extending it with the arms stretched overhead. There are a few different reasons to lift the arms overhead with the hands-in-prayer. Some are physical and some are spiritual.
1) Strengthen the shoulders. The most simple reason to lift the arms overhead is to strengthen the shoulders. Straightening the arms is one step further, especially if the hands are in prayer and not interlaced which can allow the stronger arm to support the weaker.
2) Lengthen the chest, abdomen and hips. Stretching the arms overhead draws the chest muscles tight, stretching them and drawing the ribcage upward. This has a chain reaction down the front of the body, stretching the abdomen and even the hips. It is especially valuable in backbends, hip openers like Short Man, and even front-of-leg stretches like Fixed Firm.
3) Raise the center of gravity. When we lift the arms overhead, it becomes harder to balance because we raise our center of gravity. This means that, all things being equal, arms up demands a little more stillness, awareness and control.
4) Dedication to God. Much like the well-known hands-at-prayer in front of the chest, hands-at-prayer raised overhead is a traditional form of dedication to God. Ancient ascetics would sit or stand for hours with their arms raised overhead. So raising the arms is a powerful and traditional spiritual component.
This journal honors my ongoing experience with the practice, study and teaching of yoga.
1) Sridaiva Yoga: Good Intention But Imbalanced
2) Understanding Chair Posture
2) Why I Don't Use Sanskrit or Say Namaste
3) The Meaningless Drudgery of Physical Yoga
5) Beyond Bikram: Why This Is a Great Time For Ghosh Yoga