Our exercise habits contribute more to our daily health than we might think.
According to University of Arizona nutritional scientist Richard Simpson, exercise and stress can both affect the human body's immune system. Simpson says hormones released when you exercise can be a threat to your immune system and a benefit as well.
"There are certain hormones that are released by the human body under stress and those same hormones are released by the body when we exercise," he said. "But sometimes they can have very different effects on the immune system."
Simpson is also researching the role exercise plays in long term spaceflight. He says dormant viruses could reactivate for astronauts do not follow a rigorous exercise regimen before and during a trip to the moon or Mars.