RSI and tendonitis is not the same thing. My doctor describes it better, I think, as RSS (repetitive strain syndrome). I understand that varying parts of the body can be affected such as hands/arms/neck and shoulders or legs/feet. It can be caused by many things, including tendonitis, tenosynovitis and tennis elbow to name but a few diagnosable conditions plus many others. The main thing about RSI is that it is caused by repetitive movements.