Your risk of catching a cold or the flu or developing an infection goes down if you exercise the right way. But if you exercise for too long a period of time, your risk goes right back up. In fact, your risk shoots up higher than if you did nothing at all.
One group rested in their cages. The other ran on little treadmills until they were exhausted. After three days, all the mice were exposed to the flu virus. The mice that ran until they were exhausted came down with the flu more often and had worse symptoms than the couch potato mice.
In an experiment, mice were infected with the flu virus and then divided into three groups. The first group did no exercise. The second got a moderate amount of exercise each day. The third ran all out for two and a half hours a day. After a few days, 50% of the couch potatoes had died of the flu. Only 12% of the moderate exercisers died. An astounding 70% of the mice that ran for hours died of the flu!