Thank you for your query. would you please clarify the following? 1) do you exercise regularly? or did you exercise after a long break? 2) did you warm up your muscles before exercising? 3) what kind of exercise were you doing- aerobics or weights? 4) did you feel pain or a pull while you were exercising? 5) is any part of you arm swollen or discoloured? Exercising is great when done with care. if you overdo it or do it the wrong way or do too much too soon, things can go wrong. If you were a regular exerciser and did warm up exercises including stretches and you felt some pain or pull while exercising, you may have injured a joint or sprained a muscle. on the other hand, if you muscles were not warmed up and you did too much too soon, you may have muscle pain due to lactic acid collection in your muscles. what usually happens is, when you exe cite, muscles you up energy with the help of oxygen which is brought to it by blood circulating through it. If and when it doesn t receive enough oxygen ( demand cannot be met by supply - happens when you muscles are not warmed up), it uses another energy pathway that releases lactic acid that need to be washed out through the circulating blood. if that does not happen, it collects and causes inflammation and pain. In your case, I think it is the second situation, that is the lactic acid collection since you mentioned that pain started only after two days. I would recommend some warm compresses and massage to the affected area. don t try to exert your arm and don t try to keep it still either. try to go about your normal activities. the pain should start reducing and feel better in a couple of days. if it does not, you need to get it checked to rule out more severe injury. don t wait for more than two days. If there is absolutely no improvement or it gets worse, it needs immediate attention. hope this helps and you feel better soon. wish you good health