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Exercise and Upper Respiratory Tract Infection – To rest or play?

“Doc, I’m not feeling well today, I’ve got a bit of cold. Should I go to training?”. This is a question I get asked commonly working with athletes at both the elite and sub-elite levels. To train and/or compete during an Upper Respiratory Tract Infection is one of the many challenges faced by both the sportsperson and sport and exercise physician. In this article, I will discuss what happens to our immune system during exercise, highlight some of the current literature surrounding this topic and share some practical tips I commonly use in my practice when faced with this dilemma.

What happens to our immune system during exercise?

During exercise, we switch from nose breathing to mouth breathing. This may result in increased deposition of harmful particles in the lower respiratory tract. It also causes the mucosa (lining of the respiratory tract) to dry out, which in turn slows down ciliary movement (a mechanism for clearing harmful bugs) and makes the lining more sticky (1). Immediately after moderate to high-intensity exercise lasting less than one hour, there is an increase in our virus-fighting cell count and cell activity (2,3). However, these fall below pre-exercise levels within the first two hours following high-intensity exercise (2,3). While there is also an increase in other immune cells during acute moderate physical activity, these too temporarily decrease following bouts of intense physical activity (3,4). This brief period of immunosuppression after acute intense physical activity results in an immunological “open window” whereby a sports person may be more susceptible to infection (1 -4).

What evidence is there on this topic?

While the results are conflicting, there is some evidence that intense training is associated with higher levels of infection (4,5). Nieman has proposed the J-curve, which hypothesises that regular moderate-intensity exercise decreases the risk of Upper Respiratory Tract Infection compared to sedentary individuals, while strenuous intense exercise increases the risk of Upper Respiratory Tract Infection (Fig 1) (6).

Several papers support the Nieman J-curve hypothesis that moderate, frequent aerobic exercise lowers one’s risk of developing an Upper Respiratory Tract Infection, while bouts of strenuous, high-intensity exercise may increase ones risk (7-11). Other studies looking at elite swimmers and long distance runners failed to show any clinically significant correlation between load, intensity and related illness (12,13). The exact frequency, duration, type and intensity of exercise required to optimally reduce or increase ones risk of infection is yet to be determined (5). Performing intense exercise during an infection has been associated with increased risk of heat exhaustion, post-viral fatigue syndrome and viral heart inflammation (14-17). There is no evidence that exercise will affect the duration or severity of an Upper Respiratory Tract Infection in fit and healthy people (18,7).

Will my performance be affected if I play/train/compete with an Upper Respiratory Tract Infection?

Infection is commonly used to explain poor athletic performance. Infection may compromise optimal muscle function. Exercising when ill also requires greater effort from our heart and lungs, which in theory may result in reduced performance or work capacity (5). In one study, elite long and middle distance runners reported a higher perceived training intensity while ill, however, there were no objective measurements to back this up. Another study in elite swimmers did not show any meaningful drop off in performance during competition in those with an Upper Respiratory Tract Infection in the month leading up to competition (19). Another study in elite swimmers reported that although, on average, the harmful effects of training while ill was trivial to small, the chances of harm to individuals was significant (20).

Practical Tips

  • Susceptibility to infection is multifactorial. Determinants such as genetics, nutritional status, rapid weight loss, overtraining, sleep quality, concurrent illness, certain medications, smoking, and alcohol consumption may all contribute to an individual’s susceptibility to infection.
  • Not all sore throats / runny noses are a simple, short-lived, self-limiting viral infection. There may be other causes of these symptoms that require assessment and treatment by a qualified medical practitioner.
  • Anyone with general malaise / fatigue, temperature >38C or resting heart rate >10 beats per minute above normal should avoid athletic activity until these parameters normalise.
  • In a diagnosed viral URTI, if symptoms are ONLY above the neck (runny nose, nasal congestion, sore throat), an athlete may commence training at half intensity for 10 minutes. If symptoms do not worsen, then training may continue as tolerated at mild-moderate intensity up to 80% intensity.
  • Modified training may involve more emphasis on skills rather than aerobic / endurance training.
  • If there are symptoms below the neck and/or systemic symptoms (fever, fatigue, muscle aches, severe cough, diarrhoea / vomiting) then an athlete is not recommended to train.
  • Always practice good hand hygiene before and after using communal exercise equipment and at meals. This may be either with soapy water or antiseptic hand gels. Athletes should avoid sharing drink bottles.
  • Regular, moderate intensity physical activity may not only be good for our immune system, but is also important in the prevention and management of many chronic diseases such as osteoarthritis, diabetes and cardiovascular disease. Always consult with a qualified physician before starting a new exercise program.

Happy exercising!

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