Pain is caused by pressure on the radial nerve. There are several spots along the radial tunnel that can pinch the nerve. If the tunnel is too small, it can squeeze the nerve and cause pain. Repetitive, forceful pushing and pulling, bending of the wrist, gripping, and pinching can also stretch and irritate the nerve.
Sometimes a direct blow to the outside of the elbow can injure the radial nerve. Constant twisting movements of the arm, common in assembly work, can also pinch the radial nerve and lead to radial tunnel syndrome.