Mononukleose (kyssesyke) smitter via direkte kontakt mellom slimhinner som ved kyssing. Imidlertid er det også vanlig at viruset overføres via dråper i lufta fra hosting og nysing og via hånd til munn kontakt.

Det overordnede målet med arbeidene bak denne avhandlingen var å beskrive immunologiske, hormonelle og metabolske endringer hos toppidrettsutøvere i forbindelse med en utholdenhetskonkurranse, gjennom en sesong med ulik belastning fra harde treninger og konkurranser, og i forbindelse med repeterte treningsøkter hvor restitusjonstiden mellom øktene ble variert.

The overall aim of the work behind this thesis was to describe the immune, endocrine and metabolic changes occurring in elite athletes during an exhaustive endurance race, during periods with different training and competition load, and during repeated bouts of exercise intercepted by different recovery regimes.

Exercise elicits a multitude of changes in biological functions in the body and could thus be regarded as a stressful stimulus that may disrupt a well-regulated state of homeostasis. In a stress research model, a stressful stimulus is labeled the stressor and the following response is described as the stress reaction (160;193;194).

Exercise-induced suppression of certain immune functions during strenuous training periods, increased exposure to foreign pathogens while travelling, as well as sharing the same training- and living facilities within a team may put athletes at increased risk of infections.

Traditionally, cross-country skiing has been considered a relatively safe sport with few serious injuries compared to alpine skiing or other sports like soccer.