Sprain refers to damage or tearing of ligaments or a joint capsule. Strain refers to damage or tearing of a muscle.
When excessive force is applied to a joint, the ligaments that hold the bones together may be torn or damaged. This results in a sprain, and its seriousness depends on how badly the ligaments are torn. Any ligament can be sprained, but the most frequently injured ligaments are at the ankle, knee, and finger joints.
Strains are tears in the muscle. Sometimes called pulled muscles, they usually occur because a muscle lacks the flexibility, strength, or endurance to perform a certain activity. The majority of strains occur where the muscle meets the tendon, although they may occur in the middle of the muscle belly as well.
Children under age eight are less likely to have sprains than are older people. Children's ligaments are tighter, and their bones are more apt to break before a ligament tears. People who are active in sports suffer more strains and sprains than less active people. Repeated sprains in the same joint make the joint less stable and more prone to future sprains. Muscle strains are also more likely to occur in muscles that have been previously injured.
Whitney Lowe, The Gale Group Inc., Gale, Detroit,