Which of the following best describes a strain?

A strain is best described as the overstretching of a muscle or tendon. This type of injury typically occurs when a muscle is stretched beyond its normal capacity, which can result from activities that involve lifting, twisting, or sudden movements. Strains can vary in severity, ranging from mild stretching to partial or complete tears of the muscle fibers, but the fundamental characteristic is the overstretching aspect.

In this context, the other options describe different types of injuries: a complete tearing of a muscle indicates a more severe form of injury which could be classified as a significant strain but does not encapsulate the broader definition. A fracture of the bone pertains to a break in the bone structure, which is distinct from muscle injuries. Pulling a ligament relates to a sprain, which involves injury to the ligament rather than the muscle or tendon. Thus, the correct choice focuses specifically on the nature of a strain itself.