All athletes are faced at some point with a familiar dilemma: they've got some kind of bug – a cold, sore throat, or just feeling under the weather. So what should they do? Keep on training? Or rest until their immune system has got rid of the virus? In 1998 sports scientists at Ball State University in the US provided the answer to this question.
The researchers did an experiment with 50 reasonably fit subjects aged between 19 and 29. The subjects were divided into two groups. One group trained every other day for 40 minutes at 70 percent of their maximal heart rate [EX], moderately intensive training. The subjects could choose between sessions on the stair climber, the treadmill and the bike. The other group took no physical exercise [NEX].
At the start of the experiment the researchers infected [inoculation] the subjects with rhinovirus-16 [shown below], a common cold virus. Then they monitored the development of the cold in both groups of subjects.
The cold symptoms lasted for the same amount of time in both groups, but during the first six days of the experiment the training group had fewer symptoms than the inactive group. Both groups produced similar amounts of catarrh. The subjects had to hand in their snot-sodden handkerchiefs, which the researchers then weighed to calculate the amount of catarrh produced.
The graphs below show Z scores, which indicate the amount a measurement at a particular moment deviates from the average of all measurements taken.
"Results from this investigation suggest that moderate exercise training during a rhinovirus-caused upper respiratory illness under the conditions of this study design do not appear to affect illness symptom severity or duration", the researchers conclude. "This finding is important for athletes and fitness enthusiasts alike who are interested in maintenance of their fitness levels during a rhinovirus-caused upper respiratory illness."
Athletes with a cold who train more intensively or for longer than the subjects in this study will probably delay their recovery. The same researchers came to this conclusion in a review article that they published in the nineties. [Int J Sports Med. 1994 Jan; 15(1):1-9.] Intensive exertion inhibits – partly through a rise in cortisol and testosterone levels – the immune system.
Med Sci Sports Exerc. 1998 Nov;30(11):1578-83.