Is it OK to exer­cise when you have a cold? I have been feel­ing under the weather recently with a chesty cough and runny nose, but I’m des­per­ate to leave the con­fines of my sofa. Will work­ing out make me feel worse?

There’s a rule of thumb that says, if you must exer­cise dur­ing a cold, it is OK if your symp­toms are above the neck, but not if they’re below. Personally, if I have a badly bunged-​up nose and crash­ing head­ache, the last thing I feel like doing is pound­ing a tread­mill. In fact on the rare occa­sion I get a cold, I’m secretly pleased to have the per­fect excuse to swap the gym for n extra hour in bed.

It is the second part of the rule of thumb that really mat­ters: your chesty cough sug­gests you should wait until your symp­toms have cleared up plus a couple of days, before you resume your workouts.

Exercise is in its own right a stress on the body’s immune sys­tem. During a strenu­ous phys­ical workout your body accu­mu­lates toxic waste as a nat­ural con­sequence of the extra energy it is cre­at­ing, and your immune sys­tem has to get to work on clear­ing up the res­ult­ing debris. We know that, all things being equal, this pro­cess is harm­less. Indeed, over time, reg­u­lar mod­er­ate car­di­ovas­cu­lar exer­cise helps to strengthen the body’s immune sys­tem, so you are less likely than the aver­age per­son to get ill (this is espe­cially true the older you get).

When you have an infec­tion, how­ever, all is not equal: your immune sys­tem is already busy fight­ing off the ill­ness, so it’s really not help­ful to put it under fur­ther strain with a tough workout. If you do, your cough will prob­ably take sev­eral days longer to clear up than if you res­ted up.

There’s another more ser­i­ous danger, too. If your cold is viral, or is more like flu, or you have a fever (raised body tem­per­at­ure), there’s a slight chance that the infec­tion will affect the muscle wall of your heart. Exercise in such cir­cum­stances can be extremely dan­ger­ous, and because there is no obvi­ous way of know­ing whether this is the case, the only sens­ible option is to lay off until you are recovered.

You may have been told it’s OK to do “gentle” exer­cise, and that may be true. But what is “gentle”? The people most likely to want to exer­cise dur­ing ill­ness tend to be the keen­est among us. If your idea of gentle is a steady 10km jog, you are best off lan­guish­ing on your sofa for a while longer.

Regular exer­cisers often get anxious that they will lose fit­ness dur­ing a lay­off for ill­ness. This will not hap­pen over the short-​term. Upon your return you should always go easy for the first couple of workouts, build­ing up gradu­ally over two to three weeks until you are back to your pre-​illness level of workout and feel­ing great.