Test: Lie on your back on a mat, bend your knees and position your arms straight and vertical. Now slowly lower the arms above your head, keeping the elbows locked and without hyperextending the low back or flaring the arms out to the sides. Do your arms reach the mat at full extension?
Movement: Lie on a mat on your back with your arms straight above your body, forming 90 degree angles to the mat. Keeping your elbows locked, slowly lower your arms to your sides above your head as far as you can without extending your low back. Keep your arms close to your ears.
Instructions and effects for the Lying Overhead Flexion Stretch exercise 
Movement in Sagittal Plane