This is a common yoga stretch used to open the shoulder joints and strengthen the upper back muscles. While sitting up straight, reach your left arm behind you and try to touch the space between your shoulder blades. Next, reach your right arm up over your head and bend your elbow so that your hand lands somewhere near the nape of your neck. Without causing too much strain, try clasping your fingers together. This is an intense stretch, so don't worry if you can't quite reach yet. Hold for 20-30 seconds, then switch arms and repeat.