This image of a left elbow illustrates the powerful flexor and extensor muscles and tendons of the elbow and forearm. The extensor muscles are responsible for extending (straightening) the wrist and fingers. The tendons of the extensor muscles anchor into the bone along the outer part of the elbow (yellow arrow). Injury to the tendons (tendonitis) at this location results in tennis elbow. The flexor muscles act to flex the wrist and fingers. The flexor tendons anchor into the bone along the inner part of the elbow (green arrow). Tendonitis in this location is referred to as golfer’s elbow.