I’ve been rather irritated this week. I’m so used to having such good health, that it’s really noticeable when I’m not well. I can’t recall a day off with a common cold in 25 years (although was incredibly sick with covid on a couple of occasions unable to leave the bed for days on end with high fevers and even mental confusion which was rather frightening). There have been a great many viruses doing the rounds though recently and both children, my wife and I all succumbed, We are all back to normal with respect to respiratory symptoms (although my wife has tell-tale red scabs under her nose from all the tissues!) but the post viral fatigue is, as I said as the outset, irritating.
I slept for 12 hours straight on Friday night, and topped that up with another 11 hours last night! Finally now I feel more myself. One of the most irritating aspects is knowing I should not exercise. I’m so used to training every day, I feel that I’m letting myself down, and losing fitness, very quickly. I know I should give myself a break, but I find that hard. For today’s blog, I thought I would write therefore about the question:
“Is it safe to exercise when I’ve got a cold?”
And closely followed by:
“When can I get back to training after a viral infection — and how careful do I need to be with my heart?”
The honest answer is that this sits in an area where we have some evidence, a lot of clinical experience, and a need for common sense rather than bravado. Let’s start with exercising while you’re unwell.
If symptoms are very mild and limited to the nose or throat — things like a runny nose, sneezing, or a mild sore throat and you feel otherwise okay, then very light exercise is usually fine. Think walking, gentle cycling, mobility work. Nothing hard, nothing competitive, and certainly nothing where you’re trying to hit personal bests.
Where doctors start to worry is when symptoms go below the neck. Fever, chest tightness, a chesty cough, marked fatigue, body aches, dizziness, or palpitations — those are all signs that exercise should stop. And the reason for that is largely the heart.
Viral infections don’t just affect the lungs and airways — in a small number of people, they can involve the heart muscle itself, causing myocarditis or inflammation around the heart. That’s rare, but when it happens, exercise can make it worse, and that’s why we’re cautious.
This is also why the popular “neck check rule” — above the neck you’re fine, below the neck you rest — is useful as a rough guide, but it isn’t scientifically robust. It’s a rule of thumb, not a safety guarantee. So my advice is simple:
If you have fever, feel systemically unwell, or have any chest symptoms, don’t exercise. Full stop.
Now, what about getting back to exercise after a viral illness? This is where people often go wrong — not by exercising too early, but by going straight back to their previous intensity. The key principle is this: don’t restart where you left off.
Wait until your symptoms are clearly improving, you’re fever-free, and you can get through normal daily activities without feeling wiped out the next day. Then start with easy effort only — the kind of pace where you can comfortably hold a conversation.
For most people with an uncomplicated cold or flu-like illness, a gradual return over about 7 to 10 days works well. Start with short, easy sessions. Build duration first. Only reintroduce harder efforts once you’ve had several symptom-free easy workouts. If, during that return, you notice chest pain, unusual breathlessness, palpitations, dizziness, or a sudden drop in exercise tolerance, that’s your cue to stop and get checked. Those are the red flags we take seriously in cardiology.
It’s also worth saying that feeling “a bit flat” for a week or two after a virus is common. That doesn’t automatically mean heart damage — but persistent or worsening symptoms shouldn’t be ignored.
In the rare situation where myocarditis is diagnosed, guidance is clear: no strenuous exercise for several months, followed by careful heart reassessment before returning to higher-intensity sport. That sounds dramatic, but it’s about preventing serious complications, not being overcautious.
So what’s the take-home message?
Light exercise with very mild symptoms is usually fine.
Hard exercise when unwell is a bad idea.
Returning gradually is far safer than rushing back.
And chest symptoms after a viral illness should always be respected.
Listen to your body. Be patient. Your heart will thank you for it. I’ve taken my own medicine, and prioritised stretching this last week, some very light weights mid-week (and interestingly even that shot my heart rate up way higher than normal so I backed off) and a very gentle indoor cycle yesterday wearing a heart rate monitor and keeping it very low. I’m hoping if the rain holds off I’ll get a few holes of golf in later with my son too. I desperately want to do a high intensity workout, but If there’s one thing I’d emphasise, it’s this:
Fitness isn’t lost in a few extra rest days — but pushing through illness can cost you weeks or months.