Top athletes undergoing intensive training have depressed immune systems and are more liable to infection. After competition, triathletes immune system is 70% down. Training and competing produces higher levels of adrenaline and cortisone which depress the immune system.
Cyclist Chris Boardman used to train for 3 hours a day, then changed to a specific goal oriented 45 minute session per day instead. Doing this he had no infections, and beat the record for distance cycled within a certain time.
Important not to train through infections as this leads to more problems, especially if infection affects heart and can have fatal consequences or lead to permanent ill-health or disability.
Source not recorded, date not known
