Sprains are joint injuries that involve damage to ligaments or a joint capsule, and commonly occur at the wrist, ankle or thumb.
Strains are injuries to muscles, or to the tendons that connect muscles to bones. They often affect the calf, hamstring or groin.
These injuries occur if the fibres of a muscle, ligament or tendon are stretched beyond their capacity, becoming torn. They are often due to a sudden twisting or stretching movement, or may be due to a forceful impact.
Overuse of a particular joint or muscle group can also cause sprains and strains. Factors that may contribute to overuse injuries include insufficient recovery time between exercise sessions, poor technique (for example using an incorrect golf swing), repetitive motions (e.g. doing assembly line work), and physical abnormalities.
Joints that have been injured before may be more prone to recurrent problems, especially if scar tissue has developed during the repair of the prior injury or if muscle imbalance is present.