Tuesday, July 15, 2008

The Painful Truth About Muscle Soreness

Nearly every athlete has experienced delayed onset muscle soreness (DOMS), the type of soreness that crops up 1-2 days after a training session or hard match. DOMS typically follows a bout of what might be called “unaccustomed” exercise. Soreness is first noticeable 12-24 hours after exercise, increases in intensity by 24-72 hours and then subsides within 5-7 days. After years of research, we now understand what causes DOMS and have some insight into effective treatments and prevention.

DOMS is distinct from soreness that occurs with muscle cramps, muscle strains, contusions and chronic leg pain. While these are often associated with exercise, DOMS is typically non-pathogenic. That is, if left untreated it will subside leaving no permanent damage to the tissue. During the 4-7 day soreness period, the effects of DOMS are both discomfort and loss of muscle performance. For example, force produced during a maximal contraction may be reduced by as much as 40%. Running speed can also be markedly diminished. This change can easily affect performance on the pitch by altering both technical ability and physical performance.

Through research involving both humans and animals, scientists now understand the DOMS process. We know that DOMS is not related to lactic acid or other waste product accumulation. Soreness often occurs following low intensity activities where there is little or no production of lactic acid. In fact, the presence of lactic acid within the muscle really has little or no direct effect on soreness or muscle performance. It is now clear that DOMS results from microdamage to the muscle fiber. This damage results in both pain and inflammation. In fact, many researchers now prefer the term “exercise-induced muscle damage” rather than DOMS because it more accurately describes the condition. The figure on the right is an electron micrograph of muscle fibers taken before and after exercise. It shows the extent of damage to various contractile and structural proteins.

The process begins with unaccustomed activity involving muscle contractions. Activities that lead to DOMS can range from a single muscle contraction to more prolonged exercise. The bottom line is that any time an athlete performs activities that he or she is not accustomed to, muscle soreness can develop. In particular eccentric or lengthening contractions seem to result in the most severe soreness. Another common trigger is a match or training session that is performed at intensities greater than the athlete is accustomed to. The key factor seems to be movements, activities, or intensity levels that the muscles are not accustomed to performing.

These novel contractions result in primary damage to both proteins and membranes within the muscle fiber. They also cause secondary damage by activating various enzymes and releasing calcium within the fiber that further degrade proteins and membrane structures. Within a few hours after the damage occurs, inflammatory cells and macrophages enter the damaged area. Their role is to stop further damage and begin the process of cleaning up the cellular debris - damaged proteins and membranes. Histamines, lymphocytes and prostaglandins also enter the damaged area. This results in an inflammatory response that is first noticeable by 12-24 hours after exercise and peaks between 24-72 hours. During this inflammatory response, the increased temperature and swelling triggers pain receptors which initiate the pain response. Finally, after 24 hours, the muscle begins to repair itself. Over the next few days, the pain slowly subsides as the damaged proteins and membranes are regenerated.

There are a number of theories as to how to prevent or treat DOMS. These include massage, cryotherapy (cold treatment), as well as various medications. Research into these various modalities show mixed results. A few studies show small, but positive effects on pain and muscle performance. Most of the investigations, however, show no positive effects of any of these treatment options.

The most effective treatment for alleviating DOMS and the decline in performance seems to be exercise. During the days where pain is most severe, exercising can lead to temporary relief. Stretching and low intensity exercise has been shown to reduce pain sensation and improve performance. This effect may be due to increased blood flow and elevated muscle temperature. Unfortunately, the analgesic effects are only temporary and the pain usually returns within hours after exercising. Despite this, exercise remains the most effective preventative treatment for DOMS is exercise. First, several studies show that a warm-up prior to activity can reduce the severity and duration of DOMS. It can also attenuate the loss of performance. Raising muscle temperature an increasing compliance of the muscle seems to result in less damage when unaccustomed activity is performed. A cool-down immediately after exercise does not seem to affect DOMS. This is probably due to the fact that the damage cascade has already been initiated and that performing additional, low-intensity is unlikely to halt this process.

Second, as stated earlier, DOMS is triggered by unaccustomed exercise or novel muscle contractions. Thus the most straight forward prevention is making the muscle accustomed to the types of contractions used in the activity. Research has shown that a pattern of slow progression in exercise intensity and duration will allow the muscle to adapt while experiencing only minimal damage. This concept is often referred to as the “repeated bout effect”. As the athlete repeats the bout of exercise, the protein structures and membranes within the muscle fiber adapt making itself less susceptible to injury from future bouts. In addition, the muscle adaptations lead to improved performance. Thus, it is clear that the simplest and most effective way to avoid DOMS is to train the muscle.

Unfortunately, DOMS is a common part of training and playing soccer. Hard workouts or tough matches will often result in muscle soreness the following day. Fortunately, the condition is temporary and the microdamage to the muscle fiber is not permanent. Through proper training, the muscles adapt to unaccustomed activities. This allows the athlete to avoid DOMS as well as improve performance.