A low back strain can happen suddenly, or can develop over time from repetitive movements.
Strains occur when a muscle is stretched too far and can tear, damaging the muscle.
Sprains happen when over-stretching and tearing damaging ligaments, which connect the bones together. It makes no difference if the muscle or ligament is damaged, as the symptoms and treatment are essentially the same.
Common causes of sprain and strain include:
Heavy lifting and twisting while lifting
Sudden movements putting too much stress on the low back
Bad posture over time
Sports injuries
While sprains and strains are not usually very serious and do not typically cause long-lasting pain, the acute pain can be quite severe.