What are the most common causes of tennis elbow?

Overuse of the muscles and tendons of the forearm and elbow are the most common reason people develop tennis elbow. Repeating some types of activities over and over again can put too much strain on the elbow tendons. These activities are not necessarily high-level sports competition. Hammering nails, picking up heavy buckets, or pruning shrubs can all cause the pain of tennis elbow.