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Sports and Exercise During Acute Illness: Recommending the Right Course for Patients

William A. Primos, Jr, MD


In Brief: Active people who suffer acute infectious illness may have questions concerning participation in exercise or sports during their illness. Many patients are reluctant to "get behind" on their training or "let down the team." Physical activity, however, may worsen the condition, result in impaired performance, or infect others. On the other hand, some contagious diseases are relatively benign, and some activities don't affect others. Therefore, clinicians need to understand both the sport and the illness to know what level of activity to recommend. For example, solo exercise at a reduced intensity is generally safe for patients whose symptoms are above the neck.

Although regular exercise can help improve health, even well-trained athletes develop acute infectious diseases. Most physicians advise patients to rest during an acute illness. However, highly motivated athletes and exercisers often have a variety of reasons to continue athletic activities during an illness:

  • Marcia is a 30-year-old runner training for a marathon. She develops infectious gastroenteritis. She does not want to miss a day of running and fall behind in her training schedule. Despite several episodes of diarrhea the night before, she decides to accompany her friends on their usual Saturday morning 20-mile run. The weather that day is unusually warm and humid. During the run she collapses and suffers heatstroke.
  • Mark, a 16-year-old wrestler, has influenza. Tomorrow the conference tournament will be held, which he must win to qualify for the state championships. His symptoms include headaches, chills, and myalgia. His temperature is 103° (39.4°C). Mark decides to enter the tournament. In his first-round match he loses to an opponent he had easily defeated 2 weeks before. Mark's team receives no points in his weight class and is narrowly defeated for the team championship.
  • Michelle is a 32-year-old aerobics instructor who has an upper-respiratory tract infection with rhinorrhea and a sore throat. She is scheduled to teach two classes tonight and one tomorrow morning and cannot find a substitute instructor. She slightly alters the routine for her classes, decreasing the number of high-intensity steps and increasing the time spent stretching. She is able to complete her classes, has no worsening of symptoms, and is asymptomatic 2 days later.

Patients with acute infectious diseases often have questions about participation in athletic activities. What effect does exercise have on an infection? Can physical exertion worsen the problem?

Physicians should be able to determine what level of activity is safe for their patients with infectious diseases and to explain to the patients who need restrictions why they should avoid sports. An understanding of athletes' susceptibility to infection, effects of illness on physical performance, risks of exercising during an illness, and general guidelines about determining playability will guide the physician's recommendations.

How Susceptible to Infection?

Does regular exercise and physical conditioning affect susceptibility to infection? Do athletes have altered immunity? A number of factors can affect a physically active person's risk of acquiring an infection.

Active people may be placed at increased risk of contracting infectious diseases because of increased exposure. Athletes are often in close contact with other participants who may carry pathogens. Transmission may occur through a number of different mechanisms. Training and competition often involve heavy respiration, coughing, and spitting. These acts may transmit nasopharyngeal secretions containing infectious organisms. Direct transmission may occur by bodies touching in some contact sports. Infection may also be transmitted by contact with contaminated objects such as mats, towels, and water bottles.

Some studies (1,2) have shown that intense physical training may lead to a suppressed immune system and an increased susceptibility to infection. A recent study (3) showed that natural killer cell activity increased immediately after high-intensity exercise, but decreased 1 hour and 2 hours after both moderate- and high-intensity exercise. These changes may have been due to a shift of the natural killer cells from the blood to peripheral tissues.

Eichner (4) reviewed several studies dealing with exercise and the immune system. Some showed alterations in the immune system by exercise. Most of the data, however, were inconclusive about whether the changes that occurred in the immune system were clinically important. Also, some changes in immunity in athletes may be attributable to emotional stress.

Even if exercise does not increase susceptibility to illness, physical activity may make people more sensitive to symptoms. Minor symptoms such as nasal congestion or a cough are likely to be noticed by a runner during a training session but may be overlooked by a sedentary person.

Harmful Effects

In making a decision about whether an individual should participate in athletics, a number of different factors should be considered. The primary area of concern is how exercise would affect the health of the patient. Could exercise worsen symptoms, cause complications, or delay recovery?

Strenuous exercise may result in more severe symptoms. Studies have shown that intense exercise during the incubation phase of an infection can increase the severity of the illness (1). This may be related to suppression of the immune system during exercise.

Exercising with an infection also carries some disease-specific health risks. Symptoms of a respiratory tract infection, for example, may worsen with exercise. These infections are often associated with inflammation of the airways and increased bronchial secretions. In individuals with asthma or reactive airways caused by a respiratory tract infection, strenuous exercise may cause bronchospasm, with increased cough, wheezing, and dyspnea.

Splenic rupture is a potentially fatal complication of infectious mononucleosis. Physicians restrict patients who have infectious mononucleosis from strenuous athletic activities for extended periods because of the perceived risk of splenic rupture from direct trauma or exertion (5). The decision on the proper time for resuming athletic activity is controversial, ranging from 1 to 6 months after the onset of the illness (5-8). Since only enlarged spleens rupture, and because almost all splenic ruptures occur in the first 3 weeks of illness, (6) the following criteria may be used for determining the proper time for return to athletic activity, assuming the patient is also asymptomatic:

  • For light, nonstrenuous exercise, patients can resume activity 3 weeks after the onset of the illness as long as the spleen is not markedly enlarged on physical examination.
  • For strenuous and contact sports, patients can resume activity approximately 1 month after the onset of the illness if the spleen is not enlarged on palpation. (Physical examination may not be reliable for determining spleen size. Therefore, ultrasonography should be considered for assessing spleen size in a patient who wishes to return to strenuous or contact sports before 1 month.)

Another group of diseases that might be worsened or complicated by exercise is infection with enteroviruses such as coxsackieviruses. Enteroviruses usually cause respiratory or gastrointestinal symptoms, but they may also cause myocarditis (9). (See "Viral Myocarditis: Detection and Management, July 1995, page 63.) Studies on viral myocarditis in mice found that strenuous exercise can result in myocardial necrosis and cardiac dilation, which often led to death from pulmonary edema (10). Myocarditis has also been implicated as a cause of sudden death during exercise in humans (11) and has been reported as the most frequent cause of sudden death in military recruits (12). Because of the potential for myocarditis, it has been recommended that people who have systemic symptoms such as fever and myalgia avoid strenuous exercise (11).

Impaired Performance

A different factor to consider in determining playability is impaired performance. Acute illness can hinder athletic performance by influencing several different body systems.

Cardiac function may be altered during acute infections, especially those accompanied by fever. Cardiac output and cardiac stroke volume may decrease during systemic febrile viral infections. These effects were found in subjects who were inoculated with sandfly fever virus (13). In another study (14), individuals with febrile illness showed higher oxygen uptake and higher maximal heart rate during exercise. Still another study (15) found acute disturbance of myocardial electrical and mechanical function in subjects who had viral infections.

Acute viral respiratory tract infections can affect pulmonary function. For example, research studies have shown respiratory infections to impair pulmonary gas exchange, though the impairment is not serious. A possible explanation for this effect could be mild bronchiolitis that results in mild ventilation-perfusion abnormalities (16). Additionally, rhinovirus infection may produce transient peripheral airway abnormalities, which are detected by measuring the dynamic compliance of the lungs and also are not serious. In a study by Blair et al, (17) five of eight individuals with rhinovirus infection developed increased lung compliance with higher respiration rates. These changes were transient, usually resolving in 2 weeks.

Viral infections can also affect the muscular system. Studies (9,13,18) have shown impaired skeletal muscle performance and strength during acute viral infections. One study (13) found that all subjects had decreased muscle strength and function, and another (18) showed that 9 of 10 subjects had statistically significant loss of isometric and dynamic strength and muscle endurance.

Some infectious diseases may alter an active person's fluid status. Acute infectious diseases, especially those with gastroenteritis and fever, often result in reduced fluid intake and increased fluid losses. A fluid deficit of as little as 2% to 3% of body weight stresses the circulatory system and can impair endurance (19,20).

Low levels of body fluid could also affect temperature regulation since less perspiration results in dissipation of less body heat. Although body temperature normally rises during exercise, exercisers who have a fever experience an even greater rise (21). Impaired fluid status and thermoregulation caused by febrile illness could put an active person in danger of developing heat exhaustion, heatstroke, and circulatory collapse.

Because of these effects on the various body systems, acute infectious illness may result in decreased endurance, strength, speed, concentration, or any combination of these factors. If an athlete is unable to perform adequately, the goals of the team would probably be better served by using another team member who is able to perform at a higher level.

Because of the previously discussed physiologic effects of acute febrile viral infections, it is logical to assume that working out during a viral illness would impart fewer fitness gains than would working out while healthy. Patients who are concerned about losing training time can be reminded of this supposition.

Risk of Infecting Others

Playability decisions are also affected by whether other people would be put at risk by the infected person's participation. To determine the risk of transmission, one must consider the period of contagiousness, the mode of transmission, and the type of contact. If the illness is potentially severe and is in the contagious period-and the type of contact would put others at risk of infection-participation should be avoided. Athletes should be encouraged to consider the health and welfare of others more important than their participation in sports.

Measles is an infection that can be transmitted to others through sports participation. Measles is a highly contagious illness for those who are not immune and is transmitted person to person via aerosol droplets. Measles transmission during athletic events such as the 1991 International Special Olympics and the Maryland high school state wrestling tournament has been documented (22). The period of contagiousness for measles lasts until 4 days after the appearance of the rash; people with measles should be disqualified from sports participation during this period.

Epidemic pleurodynia, or epidemic myalgia, is characterized by abrupt onset of chest or abdominal pain and fever. The usual pathogen is coxsackievirus B. Outbreaks of this disease have been reported on football and soccer teams. In an outbreak on a New York high school football team, a possible mode of transmission was shared water containers (23).

In a recent review of infectious diseases in sports in the United States, the most common disease spread by person-to-person contact was herpes simplex (24), with 12 documented reports among wrestlers and rugby players. Close contact is required for transmission. The disease can be spread either via body fluids or by direct contact of the lesions with uninfected skin or mucous membranes. The risk of transmission is increased if the uninfected skin is abraded or otherwise damaged. To prevent spread of herpes simplex, infected athletes should be disqualified from contact sports until all lesions are crusted over or healed.

Practical Advice

Physicians need to educate patients about exercising during an acute illness, limiting spread of the disease, and preventing infection in the first place (see the patient handout "Exercising—or Not—When You Are Sick"). As pointed out by Goodman et al (24), athletes should be reminded that by their participation in sports, others may be put at risk of acquiring infection. If infection could be transmitted during the sport, participation should be avoided.

In addition, athletes should be immunized against preventable diseases such as measles, mumps, tetanus, rubella, and, possibly, hepatitis B. Diseases such as enteroviral infections can be prevented by avoiding shared water bottles and towels. Also, healthcare providers need to report outbreaks of infectious diseases to public health officials to allow control measures.

Active people who do develop acute infectious illnesses should be advised that the benefits of exercise are decreased during illness and that they might as well wait until they have recovered. Patients should also be informed that participation in strenuous exercise may be dangerous to their health.

To help prevent serious complications such as myocarditis, patients can use a "neck check" of symptoms (4). If the person has only "above the neck" symptoms, such as nasal congestion, rhinorrhea, and sore throat, then he or she can probably safely try participation. However, if the patient has "below the neck" symptoms, such as myalgia, hacking cough, fever, or chills, it would be wise to refrain from intense physical activity. By following these recommendations, patients who have acute illnesses may avoid complications and make a safe return to full activity.


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Dr Primos practices primary care sports medicine in Charlotte, North Carolina, and is a charter member of the American Medical Society for Sports Medicine. Address correspondence to William A. Primos, Jr, MD, SportsMedicine Charlotte/Metrolina Orthopaedic, Sports Science Centre, 335 Billingsley Rd, Charlotte, NC 28211.