Symptoms of muscle strain include:
Muscle pain and tenderness, especially after an activity that stretches or violently contracts the muscle -- Pain usually increases when you move the muscle but is relieved by rest.
Muscle swelling, discoloration or both
Muscle cramp or spasm
Either a decrease in muscle strength or (in Grade III strains) a complete loss of muscle function
A pop in the muscle at the time of injury
A gap, dent or other defect in the normal outline of the muscle (in Grade III strain)