In terms of physiology, it is clear that many of the factors that weigh heavily on exercise performance-particularly hydration levels, blood-sugar levels, and cardiopulmonary status-are the same ones chiefly affected by certain disease states. Mononucleosis is an illness that hits many younger runners, and can cause difficulty running for quite a while.

Mononucleosis, known by many as "Mono" (Mono) is a viral infection whose effects linger for months. Younger runners are especially vulnerable. Rare is the high-school track team that escapes this illness entirely in any given year.

Rupture of the spleen, which can be fatal, is the greatest risk during the convalescent, or recovery, phase. As a result, conservatism, in the form of complete rest, is the best option. Unfortunately, a patient recovering from Mono just really needs to be a couch potato for ten weeks from the time of diagnosis. After Mono the recovery is variable from person to person, but in any case it is important to return slowly.

Mono is a particularly difficult illness for runners to deal with because of the duration of the illness and the duration of the recovery, which for each patient may differ greatly. With injuries incurred by the act of running itself, the duration of the ensuing lay-off (if any) and the mode of treatment are often well established, minimizing the uncertainty, if not the frustration, of such a setback. With an illnesses like Mono, however, things are often "touch and go"-a runner needs to rely on subtler cues in order to determine training and racing readiness, and must be aware of a variety of factors.

Unlike running with a common cold or the flu (please see my HubPages article Running with Illness: The Common Cold), running with Mono can be much more dangerous. As mentioned above, the greatest danger is the possibility of rupturing of the spleen, which can be fatal. Mono relapsed can also occurring, and instead of spending an extra day or two in bed as with the flu, Mono patients may find themselves in bed for an extra 10 weeks!

It is best to set up a plan with your doctor and to be closely monitored before and after you begin to exercise again. If you do start to exercise again and feel weak or pain, stop immediately! Give your body the proper time to recover and you will be thankful in the long run. It is probably difficult for any runner to spend 10 weeks resting, but 10 weeks is better than 20, so give yourself the proper recovery time!