Muscle strain, also known as muscle spasm or overstretching, occurs when muscle fibers are stretched beyond their normal capacity, leading to tissue damage. Common causes include overexertion, inadequate warm-up, poor posture, or underlying medical conditions. Typical symptoms include localized pain, swelling, and limited range of motion. This article is written under the professional guidance of doctors from the Department of Orthopedic Trauma and Sports Medicine at Vinmec International General Hospital.