Chapter 6 The Muscular System 197 Copyright Goodheart-Willcox Co., Inc. A lthough common, most muscle injuries are relatively minor. Fortunately, the healthy human body has considerable ability to self- repair a variety of injuries, such as those inflicted on muscles. This section describes some of the common muscle injuries and disorders. Muscle Injuries Many people think about muscle injuries as being associated with sport participation. Although injuries do occur during sport competitions, the fact is, muscle injuries also occur as people go about their daily activities. The injuries described in this section are typical. Strains A muscle strain occurs when a muscle is stretched beyond its usual limits. Someone who has a large degree of flexibility at a particular joint has a much lower risk of straining those muscles than someone with extremely “tight” muscles crossing that same joint. Another factor affecting muscle strains is the speed with which the muscles are stretched. Many strains to the hamstrings, for example, result from participating in activities that involve running, accelerating, and changing direction all at the same time. Strains of the hamstrings are a frequent problem for athletes because these injuries are slow to heal and tend to recur. One-third of all hamstring strains recur within the first year of returning to a sport or an activity. Strains are classified as Grade I, II, or III: • Grade I (mild) strains result in muscle tightness the day after the injury, but nothing more. • Grade II (moderate) strains produce pain caused by a partial tear in the muscle. Associated weakness and temporary loss of function may also occur. • Grade III (severe) strains result in damage and symptoms that are significantly greater than those accompanying Grades I and II. Grade III strains involve a tearing of the muscle, loss of function, internal bleeding, and swelling. Understanding Medical Terminology The terms strain (to muscles or tendons) and sprain (to a ligament at a joint) are very similar. Remember that Tight muscles and Tendons get sTrains. Contusions A contusion is a bruise or bleeding within a muscle, resulting from an impact. When an already injured muscle is repeatedly struck, a more serious condition called myositis ossificans can develop. Myositis ossificans involves the formation of a calcium mass within the muscle over a period of three to four weeks. After six or seven weeks, the mass usually begins to dissolve and is resorbed by the body. In some cases, a bony lesion may remain in the muscle. Cramps Muscle cramps involve moderate to severe muscle spasms that cause pain. The cause of cramps is unknown in fact, there may be numerous causes. Some of the possible causes include an electrolyte imbalance deficiency in calcium, magnesium, or potassium and dehydration. Delayed-Onset Muscle Soreness Muscle soreness is common and typically arises shortly after unaccustomed activity. Delayed-onset muscle soreness (DOMS) follows participation in SECTION 6.5 Common Muscle Injuries and Disorders Objectives • Explain the causes of common muscular injuries. • Describe the causes and symptoms of major muscle disorders. Key Terms contusion delayed-onset muscle soreness (DOMS) hernia muscle cramps muscle strain muscular dystrophy (MD) myositis ossificans shin splint tendinitis tendinosis