This is a stretch for the opponens pollicis, flexor pollicis, flexor pollicis brevis and adductor pollicis muscles.
The video clip is from the DVD “Active Isolated Stretching – Active Stretching” by Aaron Mattes and is shown here with his permission.
Information about Active Isolated Stretching, including DVDs, books, and other products, can be found atwww.stretchingusa.com