Coffee can make the pain of repetitive strain injury worse. The main thing to be considered is that the coffee will block the opiate which is the painkilling chemical receptor in the brain, which makes you more sensitive to all types of discomfort. Due to these effects of the coffee the pain of the strain injury is clearly shown and would make the victim suffer a lot. So it would be better if you avoid the coffee while you have any strain injury. Try switching to other hot drinks like herb teas flavored with honey, a caffeine free tea or plain water, milk and hot juices.