A clinical study including physical examination, electromyographic and roentgenological studies of the 2. Taekwondoists hands who mainly practiced the object-breaking maneuver with a hand who were cared at the department of orthopedic surgery, Hanyang University Hospital from November 1, 1981 to January 31, 1982, The results of the survey were as follows. 1. The average age of the athletes was 26.7 years, the average Taekwondo-practicing career was 9.7 years, the average object breaking career was 6.4 years, and the startmg age of breaking was 20.1 years in average. 2. The main parts of the hand for the breaking were Joomeok(fist) and Sonnal (ulnar edge of the palm; hand knife). 3. Bricks and tiles were commonly used as materials for breaking. Seventeen(74%) athletes could break 1 to 2 layers brick blocks, and twenty(87%) could break the 10 to 15 layers roof-tile blocks. 4. Twelve (52.1%) athletes got injuries during breaking practice. The most common injury was metacarpal fracture (7/14, 58.5%), dislocation (2/14, 16.7'lo), subluxation, sprain, and contusion (1 each/14, 8.3%) were less frequent. 5. The thickness of the knuckle pad varied from 2 to 3.9mm in 16/23 (69.5%). The average grasping power of the athletes was 97.6 1bs, and it was stronger than normal person by 9.3 lbs. 6. The electromyographic study showed no isgnificant difference in nerve conduction velocity between the af- fected and unaffected hands, which was within the normal range. It was found that the muscle primarily used was flexor digitorum profundus. 7. In the roentgenological study, the length of the second metacarpal on the affected side was the same or 0 tc 2mm shorter than the unaffected side, and when the athlete was in the growth period, the metacarpal short ness was more marked. 8. Roentgenologically no hypertrophy of the metacarpal and phalangeal bones noted.