Going Deep and Catching a Cold

I’ll always take aggregated and/or randomized data over anecdotal, but I still question whether or not a particularly hard effort can put one at risk for a cold/flu.

I’ve been training for the IMAZ 70.3, increasing my long runs. Yesterday, I did a 56 mile bike, followed by a 10k run. The run was brutal, as my fitness is not where i want it to be, and it was already 95 degrees (Tucson, AZ). I ended up walk/jogging the second half of it, and would have called my wife to pick me up, except I was too far away. So I pushed through the “bonk”. I say bonk… i was hot, i hadn’t planned my electrolytes properly, didn’t fuel properly on the bike, and the water I was drinking from my camelback was basically at 95 degrees and messing with my gut, so I probably didn’t drink enough. Walking downhill, my HR didn’t get below high zone 3. My last mile and a half was just misery.

Anway, today I’m sick. I’ve got either a head cold, or an allergy flare-up, or both. (Probably not COVID, though that’s lower on the possibilities.)

Someone please talk me out of this anecdotal event and point me back to the research that shows these events are correlated by time, not cause/effect.

Let’s start at the beginning…a cold is caused by a virus. How would “going deep” expose you to a virus?

Also, the incubation period for a cold is 24-72 hours. So if you worked out in the afternoon and woke up feeling sick, that is only 12-15 hours.

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Well you indicate it’s either a head cold or an allergy flareup. Those are completely different things caused by completely different sources.

Certainly pushing yourself hard and to the point of dehydration could weaken your immune system and make it more likely to fight off a virus.

@Power13 mentions incubation period, but we have no idea when a virus may have entered your system. It is possible that you had already contracted the virus and then weakened your immune system with the ride, which allowed it to impact you more.

You could have stressed out your system and caused it to respond to an allergen more aggressively causing allergic symptoms.

You also might just be feeling weakness within your body from pushing it too hard and not hydrating properly and misconstruing your symptoms for one of the two suggestions you’ve made. It’s really hard for anyone on this board to speculate without much detail about your symptoms and even with those, a ton of stuff might have happened before or after your ride to lead you to where you’re at now.

In general I can’t imagine pushing yourself how you describe to the point of exhaustion in high heat without water is a good thing. Take care of yourself.


I’m pointing to the idea that a lot of exertion will or won’t weaken your immune system. It’s a controversial topic in sports medicine.

I was exposed to a virus on Saturday. I’m sick on Monday. So, it’s possible I’d be sick anyway. Alternatively, it’s also allergy season and I react similarly to mild viral illnesses as I do allergies.

Also, I did hydrate well on the bike. I just didn’t account for how long my day would be with regards to fuel and electrolytes. I did consume both, but not in a strategic way.

I don’t doubt that it could be connected to training. Whether you’re sick (virus/bacteria infection) could be up for debate. Over stressing the body, especially when compounded by inadequate nutrition lowers your bodies ability to fight infection making you more susceptible to catching something.

However, serious amounts of fatigue and especially dehydration can also present symptoms similar to an infection.

I have allergies that end up leading to sinus infections at least once a year. Whenever its an infection I tend to have symptoms for a week or so. I’ve also definitely had cold like symptoms from over exertion and dehydration. For me I will wake up the next day feeling like I’m coming down with something, but usually a relaxing day and rehydrating will have that feeling kicked by the end of the day.

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What you described in your first post is more than just exertion. It was exertion past the point of bonking, in extreme heat, without proper hydration or fueling.

Any one of those three latter factors could lead to a weakened immune system. I don’t think that is especially controversial.

If you don’t give your body enough water, fuel, and keep it at a sustained higher temperature, it has to work harder to compensate, and your immune system has a chance of suffering.

Sure, it could all be coincidence, but no one on this forum is going to be able to tell you for certain one way or the other.

Because a lot of stress on your body can lower your immune system’s defenses?


As others have said, I don’t think it’s a cold, but when I go extremely hard or if I ramp up volume over an extended period, I definitely get the sniffles, scratchy throat, poor sleep, morning headache, general fatigue kind of symptoms. I just assume it’s my body screaming “take a break”.

I’ve just started looking at breathing techniques to help with recovery …

My n=1 is that when I’ve gone very deep, and haven’t focussed on fuelling the work and/or recovery enough, I’m susceptible to picking up colds. And speaking of allergies, first sign I’m tired and/or have pushed through hard workout after a poor nights sleep, is my sinus’ playing up. Very minor, but noticeable.

When I first got active, I really used to over do it (because I wasn’t following a plan) and ended up sick quite often that first winter. Similarly, one of the factors (apart from swimming and running being stupid :wink:) in me focusing on the bike and giving up triathlon was I just couldn’t recover from the multiple sessions a day, particularly getting in the swims.

Anyway, never looked into the science, just made my own assumptions. I’m actually a bit surprised there’s scientific doubt based on my own experience. But I always bow to (proven, peer reviewed) science!

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Probably just a reaction to the severe stress of that training. And/or your body was already fighting off the early stages of a cold and you’ve flattened your immune system so have less ability to deal with it.

Either way the solution is simple - don’t train like that! Train closer to home so your wife can rescue you, or go lie down in the shade and call an Uber. There is absolutely no value to be gained from digging yourself into that much of a hole in training, other than learning not to do it again…

As I think people here have noted, I don’t think there is much doubt that prolonged over-exertion without adequate recovery (over-training, in common terms) can definitely lead to less robust immune responses. Whether the actual event described was enough on its own, or more like the straw that broke the camel’s back, no one here can say. It’s not that you are exposed to more pathogens by overtraining; rather that you are potentially less adept at fighting them off. This is fairly uncontroversial (unless scientific consensus in this area has changed - if so, I’d be glad to hear).

It is also worth looking at nutrition; repeated low grade infections are very common in athletes who are restricting calories to lose or maintain a certain weight. This was talked about on a recent TR podcast (forget which one). A lack of fresh fruit and veg can also have a detrimental effect.

I think the OP would do well to have a look (or someone else take a look) at the overall training, recovery and diet picture’; everything works (or not) together.

Sure…but I have never seen anything that said one, single hard workout will lower your immune system. It is a cumulative stress issue

No one is suggesting that it is a result of a single workout

Seems to me that the OP was specifically asking about going too deep in that particular workout and thus triggerring the symptoms the next day.

Singular tense - “a particualry hard effort”

Singular tense - this anecdotal event.

Hey, look, it’s up to you whether you want to be helpful or not. Plenty of other replies here have helped the OP by pointing out that accumulated extra stress can lower the immune system, which they recognised form the overall context of the original question.

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As you note, there was an “original question”, which is what my responses were geared toward. I never said that other responses re: cumulative stress were not accurate. OP was asking re: the impact of a singular workout causing a cold. I was providing reasonable logic to show that one workout likely doesn’t cause such a response. Others provided additional context…seems like a win-win for the OP, no?

Not certain why you have your back up against the wall here, but whatever…

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Thanks for the replies. Believe it or not, this has been helpful? And it confirms why an n of 1 isn’t reliable, especially when the n is you.

I didn’t even think to factor in the cumulative stress of the past several weeks of training, which have been particularly hard.

As for giving up on swim and run… 70.3 is likely the limit of what my life stressors allow for at this point. I’ll drop back to shorter distance tris. But I can’t give up the other two, especially swimming.

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That was purely my n=1, of getting myself in hole. I wasn’t suggesting that was your solution.

There were other factors at play as well in my decision. Swimming was my real limiter (top 1/4 bike and run splits, back of pack swim), and I decided the opportunity cost of properly addressing that was too high. I enjoyed cycling, and running, much more. Particularly in the context of limited time due to family and work.