There Could Be A Hidden Downside To Intense Exercise

There's some evidence to suggest that prolonged, intense exercise - like the type that's necessary in the weeks and months before a marathon and the time of the race itself - can reduce your body's ability to fend off colds and the flu.

During intense training sessions and after a big event, several key parts of the immune system - including special types of white blood cells called neutrophils and the body's natural killer cells, the target-and-destroy agents of the immune response - appear to grind to a slow halt.

A hushed immune system would allow viruses to creep in and establish a foothold. That could explain why cold and flu symptoms are often higher for athletes during periods of endurance training, although scientists still aren't quite sure about the reasons behind this link.

Depending on the length and intensity of the workout, this period of heightened vulnerability can last anywhere from several hours to a few days.

Exercise And The Immune System

When we work our bodies to their maximum, we divert all of our resources to powering our muscles and making each breath as efficient as possible. It's an intense, taxing process.

Scientists still aren't sure why overdoing it seems to make us more vulnerable to colds and the flu, but it's not hard to imagine that hours upon hours of pushing our bodies to the limit could leave us a bit more fragile than when we started.

By comparison, moderate, regular exercise appears to have the opposite effect: people who work out at least a few times a week not only have less of a chance of catching a cold or the flu but also show symptoms for a shorter time.