Do not apply any technique with the heel of the hand while the fingers and wrist are stiff. [This can] cause undue stress to the ligaments and tendons of the wrist. The wrist must be soft and flexible when applying pressure with the heel of the hand. The fingers should be relaxed and conform naturally to the contours of the client’s body, minimizing the stress on the tendons and extensor muscles. Try to relax the elbow and shoulder joints and apply pressure with your body weight.
—from Hand Maintenance Guide for Massage Therapists by Shogo Mochizuki, Kotobuki Publications (1999)