This guy named Bob had a cold, a bad one. It started in his nose and throat, and migrated to his chest, making him sound first like Barry White and then, worse, Tom Waits.

Strep throat and bronchitis were ruled out. Bob just had a garden-variety cold. But it was enough to disrupt his nightly lap swimming, leaving Bob one grumpy guy. After a few days of hacking and wheezing, Bob went swimming anyway. Voilà. His cold symptoms steadily dissipated.

So did Bob help himself by resuming his exercise regimen while still sick? Or did his early days of rest, sans swimming, make him strong enough to eventually come back strong in the pool?

The answers may be "yes" to both questions.

No definitive studies have been published on the effects of aerobic exercise in hastening recovery from viruses. But many physicians say that, at the very least, it can do no harm. Then again, they also say a few days without that swim or run or Bikram yoga class might help, too.

Dr. Arfan Din, a Sutter West family medicine specialist and avid runner, says that, if someone used to vigorous exercise gets a cold, a workout might be a good way to fight it.

"Exercise boosts your immune system," Din says. "And boosting the immune system is a key to fighting a cold. Exercise increases circulation and gets better (air flow) into the lungs.

"The lymphatic system is where these viral particles are gathered and killed, essentially, by white blood cells. So if you're exercising, you're increasing lymphatic flow. Deep breathing by, like, running helps a lot to kill the virus in that system."

But surely someone should lie low and rest if they have a fever (101.5 or above), right? Not necessarily.

"The fever is fighting the infection, and most times you're probably not going to feel well enough" to exercise vigorously, Din says. "But you don't want to tap into the energy so much that you are fatigued. Maybe go running, but not at the same level – 20 to 30 minutes might do it."

Strength training, such as weightlifting, is discouraged for the first few days because, as Din says, "You don't want to do activities that will exacerbate that muscle achiness. Do stretches instead."

Din hastens to add that patients react differently to viruses, so there's no hard and fast rule.

"Some of it is based on a person's lifestyle," he says. "Someone who's overweight and sedentary, do we tell them to go out and run? Probably not."

Several studies have shown that endorphins released during exercise provide a psychological boost that can also aid in recovery.

Sacramento marathoner Jenny Hitchings, who recently finished fourth in her age group (40-45) in the Twin Cities Marathon in Minneapolis, has a simple rule about training when sick.

"I will run through a cold if it is above the neck," she says. "I load up on Tylenol and run easy on the treadmill or outside if it's not too cold."

However, "Once my chest gets congested or I'm coughing and wheezing, I don't exercise, as it always gets worse," she adds. "If I have a pounding headache, I can't do anything. But maybe running keeps me healthy. I really don't get that many colds."

And, to avoid spreading a virus to fellow exercisers, stay away from gyms, advises Dr. Richard Stack, a pulmonologist and infectious disease specialist with the Mercy health system in Sacramento.

"If you have a cold and go into a public facility like a health club, you're spreading around the virus," Stack says. "Just back off a few days until the virus shedding is down. The first three to five days you are going to shed the most. Then go back and work out."

Call The Bee's Sam McManis, (916) 321-1145.