Cumulative Trauma Disorder (CTD)
Occupational Overuse Syndrome (OOS)
Repetitive Motion Syndrome (RMS)

The more specific disorders are Carpal Tunnel Syndrome (CTS), Tendonitis, Tenosynovitis and a host of others. Of course CTS is the most common malady brought on by repetitive hand motion.

According to the Occupational Safety And Health Service of New Zealand, restricted blood flow is often the culprit. Lack of blood to the muscles, tendons and nerves can cause or aggravate a host of conditions, even, perhaps, arthritis. 

When you tense a muscle to just 50% of it's ability, the blood flowing through the capillaries in the muscle can be completely shut off. (Tensed muscle fibers pressure the capillaries thereby restricting the blood flow.) As the muscle is continually tensed and no fresh blood is supplied, it switches from aerobic (with oxygen) to anaerobic (without oxygen) metabolism. This produces by-products such as lactic acid which can build up and cause cell damage and pain. Subsequently, the neighboring muscles work harder to help carry the load, but because they are not designed to do the job as efficiently, those muscles fatigue (anaerobic) even faster. Muscle tension, therefore, restricts blood flow and restricted blood flow causes more tension in other muscles. If the muscles are not allowed to relax, cellular degeneration can rapidly increase as a vicious cycle takes hold. The tensed muscles also pressure surrounding nerves which causes tingling, numbness, and more subsequent injury. In addition, the lack of blood increases the likelihood of degeneration and inflammation throughout the system and, of course, retards healing. And though the cycle may stop when you rest your hands, by the time you feel any symptoms, the damage has already started. Consequently, it will take less stress to bring on symptoms in the future.

Repeated tensing of the hand can cause the fibers of the tendons running through the carpal tunnel to separate or break. (See graphic) This causes friction between the tendon and it's sheath (tenosynovium) and ultimately tendonitis. Tenosynovitis occurs when the sheath cannot properly lubricate the tendon it surrounds due to repetitive hand movement and the sheath itself becomes inflamed. Tightly gripping something for too long and forceful movements can lead to problems as well.

The best-known consequence of RSI of the hand is, of course, Carpal Tunnel Syndrome.