Resisted eccentric thumb radial abduction (extension) (Thumb radial abduction (extension) strengthening eccentric, with band, palm down)

Sit upright in a chair.
Place your affected arm on a table, with your palm facing down.
Wrap the band around your hand in a figure of 8, crossing it over at the base of your thumb.
Use your opposite hand to pull your thumb away from your palm while keeping the thumb relaxed.
Once you have moved your thumb out as far as it can go, release the thumb and slowly move it back towards your palm.