I remember my coach always recommending to cover my head and wear my coat tight when getting off the changing rooms on frosty, wintery evenings. After practice you feel so hot you could run naked on a January night. But there’s a warning in the air, you don’t want to catch a flu do you?
Jordan scored 38 with a 38 °C fever in the ’97 finals, maybe flu is not so bad.
Look again, even minor infections were linked to a drop in performance and training capacity, unless you are Michael but maybe he would have scored 58 he wasn’t sick…Let’s assume human beings want to stay healthy to perform at their best, as research kindly suggests.
Core topic: does exercise play a role on your immune system? The answer is not straightforward.
There seems to be an agreement in the field distinguishing the effect of moderate from heavy exercise on immune function. Moderate activity boosts your defences and when compared to sedentary individuals the incidence of upper respiratory tract infections (URTI) is decreased by 25-50%. On the other hand, heavy exercisers report an increased chance of contracting URTI, with their immunity temporarily depressed.
On prolonged exhausting efforts the body is under stressful conditions that may create an open window for infections to thrive and cautious behaviour is advised to reduce this risk (I’m not saying you shouldn’t have a dip in the icy ocean after a marathon, you deserve that).
Getting into the subtleties, I find interesting what causes these fluctuations in your own protective field. This is to be sought in the effects that exercise has in the production of hormones, substances released by specific tissues which act to bring an effect on targeted tissues, such as cells with immune function.
Exercise was found to affect the inflammatory state of the body, this through the effect of hormones released during exercise by tissues like muscles. Particularly, interleukin-6 (IL-6) has is one of the main determinant of the anti-inflammatory effect that makes exercise the best cure against chronic diseases in which there is a persistent inflammatory state, such as atherosclerosis.
Moderate exercise is also acutely increasing the recirculation of immunoglobulins, neutrophils and natural killer cells for a period of 3 hours post exercise and URTI symptoms decrease when training regularly for 12-15 weeks. This are the possible mechanisms that may account for an enhanced immune function of regular exercisers.
When training hard things are different. A great effort produces a much larger release of cytokines IL-6, IL-1ra and IL-10, to the extent that these substances affect the balance of the immune cells by inhibiting type 1 T-cells cytokine production. The latter represent the cell-mediated response of the immune system and are the main defence from infections and viruses. Overall, strenuous exercise decreases pathogens protection and inflammatory state acutely for a period of 3-24 hours post exercise, after which immune function is restored.
We might want to restrain IL-6 release to avoid this post-exercise black hole and keep infections out of the body. This is possible with vitamin C supplementation or other nutritional strategies. Indeed ultramarathon runners had lower URTI incidence with vitamin C long term intake and this may account for the reduced production of IL-6, but there’s a catch.
IL-6 plays a key role in exercise adaptation to training and limiting its production may affect performance by impairing recovery. Even worse, IL-6 is probably the crucial anti-inflammatory substance that promotes the optimal health of a regular exerciser and altering its concentration might prevent one of exercise greatest benefits.
This is indeed a double-edged sword where on one hand you might improve your protection from infections while on the other you might impair body healing, training improvements and increase your whole-body inflammation state.
Think about it.
Nieman 2011 Clinical implications of exercise immunology
Gleeson 2011 Influence of training load on upper respiratory tract infection incidence and antigen-stimulated cytokine production
Gleeson 2007 Immune function in sports and exercise