Muscle Strain

What Is It?

A muscle strain is the stretching or tearing of muscle fibers. In mild cases, only a few muscle fibers are stretched or torn, and the muscle remains intact and strong. In severe cases, however, the muscle may be torn and unable to function properly.

Doctors often classify muscle strains depending on the severity of the damage:

• Grade I strain - Mild strain; only a few muscle fibers are stretched or torn. Although the injured muscle is tender and painful, it has normal strength.

• Grade II strain - Moderate strain; with a greater number of injured fibers and more severe muscle pain and tenderness. There is mild swelling, noticeable loss of strength, and sometimes a bruise.

• Grade III strain - Strain that tears the muscle all the way through, sometimes causing a "pop" sensation as the muscle rips into two pieces or shears away from its tendon. These are serious injuries that cause complete loss of muscle function, as well as pain, swelling, tenderness and discoloration. Because Grade III strains usually cause a sharp break in the normal outline of the muscle, there may be an obvious "dent" or "gap" under the skin where the ripped pieces of muscle have come apart.

Although the risk of muscle strain is especially high during sports activities, you can strain a muscle by lifting a heavy carton or stepping off a curb. In the United States, strains and sprains account for more than 4.5 million doctor visits every year. More than one-third of the injuries happen to active young adults between the ages of 25 and 44. Men are about 30% more likely to be injured than women. On the job, strains, sprains and tears account for four out of the top five categories of injuries among American workers.

Almost all athletic activities carry some risk of muscle strains, though they tend to happen most often in contact sports, such as football, and in sports that require quick starts, such as basketball and tennis. Among high school athletes, strains account for about one-third of all injuries in baseball and about 25% of all injuries in soccer, football and volleyball.