Tennis elbow is a type of tendinitis -- swelling of the tendons -- that causes pain in the elbow and arm. These tendons are bands of tough tissue that connect the muscles of your lower arm to the bone. Despite its name, you can still get tennis elbow even if you've never been near a tennis court. Instead, any repetitive gripping activities, especially if they use the thumb and first two fingers, may contribute to tennis elbow. Tennis elbow is the most common reason that people see their doctors for elbow pain. It can pop up in people of any age, but it's most common at about age 40.