"I personally have experienced it several times after several races...a little more fatigue a fever runny nose," said Michael Conlon.
Part of it is the body reacting to the inflammation. But research has shown that 72 hours after the race, marathon runners are also more likely to get a cold.
The high intensity exercise increases production of a hormone called Cortisol which weakens the immune system.
Cortisol is a stressed response hormone and when it's elevated it works directly on certain cells that help fight bacteria or viral illness.
But a moderate amount of exercise has the opposite affect it's been found to boost the immune system and increase the number of macrophages the immune cells that kill the bacteria
So how much exercise is too much? Dr. Christopher Ahmad who's a marathon runner himself and also a sports medicine specialist and head physician for the Yankees says less than an hour is ideal for most people
"Things that go beyond 60-90 minutes of endurance exercise that's been shown to be near the threshold of overexertion...So for example, if you're a female getting into an exercise program you do a brisk walk several times a week your chances of getting the common cold are less then let's say someone who doesn't exercise," he says.
For those who insist on intense, Jeff Dengate from Runners World Magazine says he starts his recovery right after the race.
"Get off your feet take the next 72 hours easy kick your feet up take time off work if you can rest up and recharge," he said.
LINK: RUNNERS WORLD