A Sore Subject - muscle soreness

American Fitness, March, 1999 by Deborah Riebe

Understanding the causes of muscle soreness and taking steps to prevent it.

Muscle soreness is common following unaccustomed exercise. It often occurs in sedentary people who begin a fitness program, but also among well-trained athletes who try a new workout routine. Although low levels of soreness are acceptable, extreme levels are counterproductive to the normal progression of an exercise program.

Types of Muscle Soreness

Muscle soreness present during a workout or the subsequent recovery period is referred to as acute. It is caused by a reduction in blood flow to the muscle (Wilmore and Costill, 1994). This leads to an accumulation of the metabolic by-products of exercise (hydrogen ions from lactic acid) within the muscle tissue. These by-products stimulate pain receptors, but the pain and soreness usually disappear when you stop exercising or shortly thereafter.

Muscle soreness felt a day or two after a heavy bout of exercise is called delayed onset muscle soreness (DOMS). Following a mild to moderately intense new exercise routine, some muscle soreness may be present for 24 hours. Priscilla Clarkson, M.D., an expert in the area of muscle soreness, has found a very intense regimen may result in soreness that lasts up to a week. Severe soreness can limit the activities of daily living, resulting in difficulty performing simple tasks such as walking up stairs or sitting down in a chair.

What Causes DOMS?

Experts generally agree soreness felt one to two days after a workout is partially caused by structural damage to muscle fibers. W. Stauber, M.D., and colleagues used a high-powered microscope to analyze muscle fibers after an intense workout. It was clear that cell membranes ruptured and other structural components were disrupted. However, Clarkson reports the damage to muscle fibers is relatively small, with less than 5% of the tissue affected. Damage is not limited to one area, but occurs throughout the muscle fiber.

Microscopic muscle damage causes an inflammatory response. This process contributes to muscle soreness in two ways. The accumulation of fluid (swelling) causes pressure. Also, white blood cells, which serve as a defense system in the body, enter muscle fibers and secrete chemicals that activate pain receptors (Byrnes and Clarkson, 1986; Smith, 1991).

Although the causes of DOMS are not fully understood, scientists have eliminated some factors once thought to cause muscle soreness. It was long believed lactic acid and muscle spasms caused DOMS. They do not. Lactic acid dissipates from muscle shortly after exercise and is not present when muscle soreness develops. Electromyography (EMG) has shown muscles are not in spasm when they are sore.

The Eccentric Connection

Eccentric muscle actions (those in which tension is produced while the muscle is lengthening, such as the lowering phase of a bicep curl) cause the greatest muscle soreness. Gravity pulls the barbell down, and your bicep opposes this gravitational pull to lower it slowly. Eccentric contractions are commonly referred to as negatives.

Studies demonstrate eccentric contractions cause more muscle soreness than concentric contractions in which tension is produced while the muscle is shortening. In one study, subjects were asked to run on a treadmill on two separate days, one day with a level grade and the other with a 10% downhill grade. No muscle soreness was associated with level running. However, downhill running required extensive eccentric action, which resulted in considerable soreness.

Priscilla Clarkson, M.D., and colleagues found eccentric contractions not only result in muscle soreness, but a significant decrease in muscle strength. In their laboratory at the University of Massachusetts, they used bicep curls consisting of repeated eccentric contractions (two sets of 35 maximal eccentric actions) to induce severe muscle soreness. This resulted in a 50% loss of strength, which did not return to normal for at least a week. Furthermore, the study subjects reported muscle stiffness following this bout of exercise and were unable to fully straighten their arms without pain.

Although eccentric actions are more damaging to the muscle than concentric actions, they should not be eliminated from an exercise routine. Complete repetitions involving both the positive and negative components are essential for maximum strength gains.

Is Fatiguing Muscle Necessary for Improvement?

William Kraemer, Ph.D., and Steven Fleck, Ph.D., suggest fatiguing muscle tissue can be beneficial. An overload on a muscle resulting in slight tearing of its fibers may be accompanied by some soreness. During the repair process, muscle tissue rebuilds, remodels and is ultimately strengthened.

Through muscle adaptation, an individual can continue to train with less damage occurring (Clarkson, 1997; McCardle, Katch and Katch, 1996). This phenomenon is familiar to most individuals who weight train. The first few weeks of training results in soreness after the workout, but this eventually stops (even with more weight added, unless an extreme jump in intensity is made). This is called the repeated bout effect. Performance of one exercise bout makes the muscle less susceptible to damage.