Any repetitive action can give you repetitive strain injury (RSI), of which tennis elbow is form. I got RSI from a combination of a lot of computer keyboarding at work and playing my recorders. The Doctor told me to lay off for a month to give the damage time to heal and then to be careful afterwards as there will always be a weakness. I took up concertina about 15 months ago and find occasionally I get problems in my wrist, so I have to go easy. With the concertina, finding a relaxed position for arms and wrists seems to be critical so that they are not strained. If they are the finger movement can aggravate the weakness in the muscles there for me. I play Anglo and I got a tip about putting some foam on the handles under the strap to keep the wrists straight, otherwise they are pulled back a little and that creates problems. English Concertina is held differently - supported by the thumbs and little fingers. The one time I tried it I found it uncomfortable, but but my RSI was playing up a bit at the time which may have aggravated the problem.

I suggest you go to concertina.net to find out more about the different types. Their forum has a section on health problems which is worth looking at. I find the people there very helpful to genuine queries.