Pain and other chronic shoulder problems may be caused by sitting at a tablet computer or touch-screen keyboard for extended periods, according to a new study. Researchers compared the physical impacts of working on three kinds of keyboards. Their findings were published in the November edition of Applied Ergonomics.The study concluded that using touch-screen or virtual keyboards entails less typing force and finger-muscle stress. Working with a tablet, on the other hand, requires holding the fingers in a suspended position above the computer to avoid accidentally pressing a key. That may result in “static loading” in the shoulders, according to the researchers at Northern Illinois University in DeKalb, Ill. Nineteen experienced users of touch-screen keyboards (10 men and nine women in their mid-20s) participated in the study. They typed portions of “Grimm’s Fairy Tales” in five-minute increments on virtual, desktop and notebook keyboards. Electrodes recorded muscle activity in the forearms and shoulders, while a force platform under the computers measured keystroke force, the Wall Street Journal reported.On average, the volunteers typed 63 words per minute on the desktop and notebook keyboards; and 25 words per minute on the touch screens. When using the virtual keyboards, they made more mistakes but required less muscle activity.The trapezius muscles in the upper back were strained to a greater degree with touch screens than that experienced while using the other types of keyboards, possibly because of “hand and forearm floating,” the researchers wrote. This is called parascapular myofascial pain. They suggested that prolonged use of touch screens can lead to muscle damage.The study, funded in part by Hewlett-Packard Co., was titled “Differences in Typing Forces, Muscle Activity, Comfort and Typing Performance Among Virtual, Notebook and Desktop Keyboards.” Orthopedists frequently treat patients who suffer shoulder pain and inflammation that results from overuse or injury. The bony structures or soft tissues can deteriorate due to long-term, repetitive strain.The pain often happens only when making certain movements, though chronic and persistent discomfort also can occur. Sometimes, resting the shoulders can make the pain go away. Simple prophylactic measures like taking a 5 minute stretch break every hour can help avert this ailment. In other cases, orthopedists prescribe treatments ranging from physical therapy, acupuncture, oral medication, or surgery. The most commonly diagnosed causes of shoulder inflammation are bursitis, tendonitis and tendon tears Irritation of muscles in the neck and posterior shoulder is called myofascial pain. Repetitive straining of the shoulders can cause inflammation of bursae, tiny sacs of fluid that reduce friction between muscles and bones within the shoulder blade. When the bursae become irritated and swell, subacromial bursitis can develop. When the arm is lifted, the acromion rubs on tendons and bursae in the rotator cuff. Impingement lead to limits in shoulder range of motion. The situation also can lead to a rotator cuff tear. Patients diagnosed with this condition typically also experience rotator cuff tendonitis. The pain can be severe enough to limit simple, everyday activities.Long-term deterioration can cause a tendon to split or tear. A complete tear is the severing of a tendon into separate pieces, which usually detaches it from the bone. The injury most frequently is diagnosed in the rotator cuff tear or biceps tendon tear.