The change of season’s cold is here and I’m sure for many of you the office air conditioning has helped spread Joe Bloggs’ cold onto you – even though he’s on level two.  Regular cycling of light to moderate intensities can increase your immune systems fight against infections, while prolonged high intensity training, and racing can reduce it.  Elite cyclists tend to have higher incidences of infectious monocleosis (glandular fever), and upper respiratory infections than recreational cyclists and illness is common in those experiencing overtraining syndrome. 

Our immune system

Our cardiovascular and lymphatic systems comprise our immune system and function together in resisting infections.  Our cardiovascular system consists of our heart, lungs, and systemic circulation (veins and arteries around our body).  Our lymphatic system is a vascular network involved in fluid and molecule distribution therefore both systems are important in blood and fluid transport and therefore immune function.  Specialized filters spread throughout our lymphatic system, called lymph nodes are vital for the immune function (our body’s defense against a foreign material). 

Our immune system also consists of a number of blood and lymphatic cells, including phagocytes (granulocytes, monocytes, macrocytes, eosinophils, neutrophils, basophils), natural killer cells, lymphocytes (T and B cells), and proteins (antibodies Ig’s, complement and lymphokines).  Each of these cells and proteins has specific functions in our defense again foreign materials and maintenance of normal levels is essential.

When are you most at risk?

Homeostasis is the word used to describe maintenance of normal physiological function.  When we ride our bikes, we stress our bodies, and it responds by attempting to maintain homeostasis.  To re-establish homeostasis concentrations of circulating immune cells changes during cycling, immediate recovery after cycling and chronically in response to cycling.  The increase in these cells and proteins typically occurs in proportion to moderate and intense exercise.  The increase is greater for prolonged exercise (>2hrs), however during prolonged high intensity rides lymphocyte levels decrease, with circulating levels returning to normal within 2hrs of recovery (however these responses are specific to the individual).  Bacurau et al, (2002) tested the effect of carbohydrate supplementation on immune response to exercise in 12 cyclists performing repeated bouts of high intensity exercise (total 4hrs).  They found that immune response was positively enhanced in the cyclists that supplemented with carbohydrate throughout the session.

Long term, high intensity training has also been associated with decreased immune function, including decreasing lymphocyte concentration and natural killer cell activity.  Extended periods of training like this can lead to overreaching and overtraining.  Some overreaching is necessary to acquire a training effect, however extended periods induce overtraining (imbalance between training and recovery resulting from training and/or non-training stress resulting in a decrease in performance capacity).  Resting antibody concentrations have been shown to decrease 18-32% in athletes showing symptoms of overreaching, and with such large reductions in the body’s defense system incidence of infections increases. 

Practical pointers to help your immune system:

• Increased energy for to keep the body warm in winter requires increased caloric intake.
• Increase carbohydrate intake in training/racing where you think you are particularly prone to sickness.
• Avoid overreaching too much, increasing rest and recovery after completion of high volume training cycles or racing.
• Limit prolonged training blocks of high intensity training.
• Get into the habit of having regular blood tests to establish normative values for yourself to prevent overtraining, and make sure you get a copy for future comparisons.

References:

Bacurau, R.F.P., Bassit, R.A., Sawada, L., Navarro, F., Martins, E., & Costa Rosa, L.F.B.P.  (2002).  Carbohydrate supplementation during intense exercise and the immune response of cyclists.  Clinical Nutrition, 21(5); 423-429.

Halson, S.L., Lanchaster, G.I., Jeukendrup, A., & Gleeson, M.  (2003).  Immunological responses to overtraining in cyclists.  Medicine and Science in Sports and Exercise, 35(5), 854-861.

MacKinnon, L.T.  (1992).  Exercise Immunology.  Human Kinetics Publishers, Monograph 2, Current Issues in Exercise Science Series.

MacKinnon, L.T.  (2000).  Chronic exercise training effects on immune function.  Medicine and Science in Sports and Exercise, 32(7 Suppl.), July. S369-S376.

Robergs, R.A., & Roberts, S.O.  (1996).  Exercise Physiology.  Mosby Inc, St Louis.