The majority of injuries in sports can be attributed to overuse. In tennis, for example, it is the consistent swinging motion that leads to repetitive stress injury. The most common symptoms are a pain in the forearm and elbow.
If the area is swollen or bruised, it could indicate an underlying problem such as a dislocated shoulder. A doctor can perform an X-ray or MRI to determine if there are any fractures in the arm and provide immediate care. If the arm is not painful, there are no fractures and the area appears normal, you should begin treatment to prevent further injury.