The wrist flexors are the muscles on the underside of the forearm. When they’re chronically tight, Golfer’s Elbow can develop. This exercise is useful whether the muscles are just tight, or alongside osteopathic treatment for golfer’s elbow.
Take a spiky ball (I’m using one of the smallest from this set), and rest your arm on top, with the muscles on the inside of the forearm making contact. If the table provides too much pressure, apply less pressure or use your hand instead.
To make the exercise stronger, you can bring your wrist back and stretch the muscles further. Ask your osteopath if they would recommend heat or ice before or after to further increase the effectiveness.