However, those who ran less than 16 kilometres per week had had the lowest odds for becoming ill. At more than 27 kilometres per week the odds doubled, suggesting that as volume is increased so is the chance of infection. Surprisingly, there is also a link between psychological stress and the immune system. During episodes of psychological and emotional stress periods there is an increase in circulating adrenaline, cortisol, and neuropeptides, which will have a detrimental effect on the immune system. Furthermore, during racing there is often psychological stress, which might further affect the immune system.
Glutamine metabolism is of vital importance for lymphocytes.
A decreased amount of glutamine has a direct effect on lowering the proliferation of lymphocytes. Exercise can decrease the amount of glutamine. However, research has failed to completely satisfy whether exercise induced reductions in glutamine is correlated to decreased immunity. During exercise as CHO is oxidised and muscle glycogen is used and depleted, stress hormones are released that depress the immune system. By using a CHO drink during and post exercise, plasma glucose concentration is better maintained and changes in immunity are reduced.