The ligaments, muscles, and tendons work together to handle the external forces the spine encounters during movement, such as bending forward and lifting. Sprains and strains are similar disorders affecting different soft tissues in the spine. Sprains are limited to ligaments whereas strains affect muscles, tendons, or muscle-tendon combinations. Ligaments are strong flexible bands of fibrous tissue. Although ligaments are resistant to being stretched, they do allow some freedom of movement.
Muscle is made up of individual and segmental strands of tissue.
When back muscles encounter excessive external force, individual strands can stretch or tear while the rest of the muscle is spared injury. To illustrate a sprain or strain, consider what happens when lifting something heavy. Initially muscles are recruited to manage the load. When the load or force exceeds the muscles' ability to cope, the force is shared with the ligaments. When a ligament is stressed beyond its strength, it can tear.