Scare Tactics to Prevent You From Exercising While Sick
Your training has gone well. You have built up your base and gradually added intensity to your training regimen. You have completed key workouts in record times.
But with only a couple of hard workouts to go before the big race of your season, you notice a tickle in the back of your throat. The next morning you have a sore throat, headache, and cough and think that you might have a fever. A tempo run is on your agenda. What should you do?
Take Care of Yourself
If you think that you have a simple cold without systemic symptoms, exercise at a low heart rate and easy level of perceived exertion (long-slow-distance pace or easier) for a short period of time. If you are any sicker than stuffy-nose-sick, you should skip the run altogether.
Adhering to the following recommendations may help you recover faster and could even save your life.
1. Never exercise with a fever, lower respiratory tract infection, or symptoms of systemic illness (muscle aches, chills, malaise, etc.).
2. Do not ignore symptoms that could be attributable to the heart, including shortness of breath, irregular heartbeat, fainting, chest pain or lightheadedness. See a doctor immediately if you have any question about the health of your heart.
3. Remember to have reasonable and lowered performance expectations after you‘ve been ill.
4. Listen to your body and practice restraint. Wait to resume training until your motivation and health have completely returned. You have only one body, take care of it.
Now lets look at the “whys” behind exercising caution in training when you‘re ill.
Metabolic Response to Infection
Acute infection results in a biological response that could be equated with calling out the National Guard. This acute phase response involves chemicals being produced throughout the body (white blood cells, the cells lining blood vessels and the airways, etc.). Evolutionarily, this process increases a sick person’s chances of survival.
Nutrients are mobilized (e.g., amino acids, the building blocks of protein), which the sick person uses to make infection-fighting substances. The acute phase response is stereotypical, or essentially the same regardless of the cause of the infection. Like any good military operation, the magnitude of the response is generally well-regulated and determined by the intensity and duration of the threat.
Protein Catabolism
During an infection, the body becomes catabolic (the opposite of anabolic) and breaks down muscle protein. The degree of muscle catabolism and protein loss is related to the height and duration of the fever caused by the infection.
Unfortunately, there is no evidence that controlling a fever with acetaminophen or ibuprofen decreases this loss of hard-earned muscle.
The amino acids that are liberated from muscle are scavenged by the liver and used as an emergency energy source (glucose production via gluconeogenesis) and as the building blocks for acute phase proteins, which the body employs to fight infection.
Your muscles have many good reasons to ache when you have an infection. Skeletal muscle is the main source of catabolized protein, but heart muscle contributes as well. Skeletal muscle biopsies done in feverish people and laboratory animals during acute infections demonstrate microscopic evidence of muscle damage.
The same chemicals that initiate muscle breakdown during infection also inhibit effective muscle building and repair, making it virtually impossible to build muscle during any infection more serious than a cold.
Unfortunately, you can’t even lose body fat while you are sick, as fat metabolism is impaired during infections. This causes the sick person to rely more heavily on muscle as an energy source than it normally would during times of physical stress (e.g., starvation or heavy training). So any weight loss during a febrile illness is generally lean muscle mass.
During a febrile or systemic illness, athletes should be wary of stressing muscles that are actively being broken down to fuel the body’s defenses. Normal recovery after a workout can be greatly prolonged and the risk of injury may be heightened.
Studies have shown a 25 percent decrease in isometric muscle strength after a simple febrile illness such as the flu. Replenishing muscle mass lost during a three-day febrile illness may take up to two weeks.
Aerobic Metabolism
The ability to perform aerobic metabolism, the primary energy source during long-distance training and racing, is impaired during infection. Studies on rats forced to exercise during an experimental infection show a substantial decrease in performance-related metabolic capacity.
Concentration of enzymes integral to aerobic metabolism are diminished in muscle biopsies of infected humans. Lactate threshold (anaerobic threshold) and maximal oxygen (VO2max) uptake are depressed during and following an infection. It can take one to three months for an athlete to fully recover pre-illness levels of aerobic enzymatic efficiency.
Myocarditis
Myocarditis, inflammation of the heart muscle, is one of the more common and most serious complications of an acute (usually febrile) infection. While many viruses and some bacteria can cause myocarditis, a family of viruses called the enteroviruses are the most common culprits.
Unfortunately, a good physical exam and history performed by your doctor is unlikely to determine the exact cause of your fever and muscle aches. Your doctor won’t be able to tell you whether your symptoms are caused by a rhinovirus (causes the common cold and is rarely associated with myocarditis) or an enterovirus (which carries a relatively high risk of myocarditis).
Myocarditis without obvious symptoms is relatively common. In a careful epidemiological study of Finnish military recruits performed during the 1980s, the annual incidence of unequivocal myocarditis was a modest 0.02 percent. However, during acute infections, 1.2 percent of sick recruits had evidence of myocarditis on electrocardiograms and blood tests. During an epidemic of influenza A, the incidences rose to 7.7 percent. The majority of affected recruits had no cardiac symptoms.
The relative frequency of myocarditis during the flu wouldn’t be a big deal except for an important fact: Vigorous exercise worsens this potentially life-threatening condition. Animal experiments demonstrate that exercise increases viral replication in heart muscle, resulting in more inflammation and destruction of heart muscle.
Sudden death during exercise is often caused by myocarditis. At autopsy, the hearts of athletes who suffered sudden, unexpected deaths often show microscopic signs of myocarditis, including inflammation and dying cells. Genetic material from a variety of viruses and bacteria has been isolated from these inflamed hearts. An arrhythmia (disturbance of heart rhythm) caused by myocarditis is the presumed mechanism of death in these otherwise young, healthy people.
Between 1979 and 1992, 16 elite Swedish orienteers suffered unexpected cardiac death. The majority of these athletes had blood tests consistent with a recent infection and autopsy evidence of myocarditis. Since instituting strict prohibitions against exercising while ill, no further Swedish orienteers have suffered sudden death.
Even after an episode of acute myocarditis is over, there can be long-term consequences. Inflammation can scar the heart muscle. These scars can be where potentially fatal arrhythmias start and these heart rhythm disturbances can change or even end your life. This process of inflammation and subsequent scarring of the heart muscle is one of the hypotheses for the origin of Greg Welch’s career-ending difficulties with ventricular tachycardia.
In summary, hard exercise when you have anything more serious than a cold is unlikely to result in significant physiological gains. Training under these circumstances will be of lesser quality, and may even lead to serious consequences.
You are more likely to perform well in your goal race–and in life–if you occasionally learn to kick back and rest, rather than trying to fit in one more hard workout.
Source: A. Marc Harrison, MD Triathlete magazine
