You can cut the number of colds you get per year, as well as reduce the severity of symptoms and duration of a cold by nearly 50%.
A study published in the British Journal of Sports Medicine has shown that being fit and exercising 5 days per week can significantly reduce the duration of colds and the severity of cold symptoms by between 32 and 43%, compared to those who exercise one or fewer days per week.
Caution is headed though, as previous studies have shown an increase risk of colds if one exercises too hard too often, referred to as overtraining, as well as increasing risk of repetitive strain injury and injuries in general.
Damed if you do, damed if you don't?
Exercise frequently and within your means.. don't overdo it and you'll be healthier and more fit.