By Dr Dan Laptoiu, MD, Bucharest, Romania

Muscle strain refers to a tearing or pulling injury to muscle.  This can occur in any muscle group.  A good example of a muscle strain is the "hamstring pull" (back of the thigh).  Strains will cause muscle pain with any attempted muscle flexion).  Later, patients may experience spasm (involuntary tightening) of the muscle that can increase the pain.