Ah, frustratingly enough, it all depends on who you ask.
Some fitness gurus, like Dr. Joshua S. Fink, who is both a physician and a personal trainer who runs training centers called Prescriptions for Fitness, Inc. in Ridgefield, CT and Chappaqua, N.Y. said the simple answer is that if you’re sick, don’t exercise.
“You can use four letters, S-T-O-P,” he said. If you exercise while your viral infection is at its worst, which is from the 24 hours before onset of symptoms until three days later, “you decrease your immunity to fight a cold.” Immune cells called natural killer cells “decline if you exercise while you’re ill with a cold,” he said. Don’t go back to training until you truly feel better. “What we’re looking at here is being out of commission for five to seven days. There are 365 days in the year….Learn when to chill out rather than thinking, ‘No guts, no glory.’ ”
Once you resume training, he said, follow the “50 percent rule.” Do half your usual exercise for half the usual time – in other words, if you usually do 30 minutes of exercise at a heart rate of 130 beats per minute, work out for 15 minutes at 75 beats per minute. Then gradually build up to normal.
Exercise physiologist Roger Fielding of the Sargent College of Health and Rehabilitative Sciences at Boston University took a slightly different view. You have to use your own judgment, he said, although you definitely should not exercise if you have a fever. If your cold symptoms are localized to your upper respiratory tract and you have no body aches, exercise if you feel like it. “I am nursing a cold right now,” he said. “I ran yesterday outside and I am going to run today.”
In a study several years ago published by the American College of Sports Medicine, researchers gathered 50 college students, divided them into two groups – one that did supervised exercise and one that did not – and then intentionally gave them all colds. There were no significant differences on a number of measures, including “mucous weight measurement” and symptom severity scores, the study found.