Tennis elbows anyone? I have been seeing a lot of sore forearms and elbows lately. Considering I work primarily on CrossFit athletes this is a strange title for an injury since most of them do not play tennis. Tennis elbow is caused by the overuse of the arm, forearm and hand muscles, which causes pain in the outer part of the elbow.Read more: Got Tennis Elbow? Massage Can Help Relieve it.