I’ve completed 963 races on Zwift, but the number of races I’ve DNF’d can, I think, be counted on one hand.
This isn’t because I’m some mental or endurance giant. It’s just because I hate getting geared up for a race, then pulling out before it’s done. So even if I get dropped, and even if it’s because of some strange mechanical or technical issue, I’ll almost always keep pedaling to the line.
But last Saturday’s race was a bit different. Here’s how it unfolded…
The Warmup
The race began at 9:30am, so I was planning to be on the bike by 9am to spin up the legs with Coco. I had chewed two pieces of caffeine gum and applied PR lotion to the legs… my typical race prep. But I got distracted processing Tiny Race results and ended up with only 15 minutes to warm up.
The shorter warmup wasn’t a big deal, but I did note that it felt harder than usual to produce high-end power, and my heart rate seemed a bit higher than normal. Typically I can chug along in the Coco group at ~125-130 bpm, but today it was more like 135-140.
This wasn’t altogether surprising, as I’d been a bit sick for a few days. It was one of those annoying cold/flu bugs where your nose is running just enough, you’re forced to cough just enough, and you’re feeling just tired enough to know you’re sick. I wouldn’t have called myself super sick. Generally, I try to pretend I’m not sick anyway, so I wouldn’t have even called myself sick. Just a “bit” sick.
I was hopping into this race, hoping the sickness was minor and wouldn’t affect my riding. But I was beginning to think that wouldn’t be the case…
The Plan
The race (part of the EVR Winter Series) was on 2 laps of London’s Greatest London Flat, a course that generally lives up to its name even though that longer, slack climb in the Richmond Park area always feels a bit too suffery:
This race used two settings I typically don’t see in the races I frequent. First, all categories began together. Secondly, double draft was enabled. So I joined, hoping I’d be able to ride smart and stay with the A’s in front for the duration of the mostly-flat race.
Lead-In and Lap 1
We began with 143 riders across all categories, but the first selection happened quickly, with a front group of 58 riders consolidating in less than 3 minutes. Then we hit the short Northumberland Avenue climb up to Trafalgar Square and the group was whittled down to 48. (Most of the front riders were A or B category, although a few cagey C riders had snuck in.)
As we finished the lead-in I saw a message from “Old Andy”, a rider I had raced recently in Makuri Islands where we found ourselves together, unsuccessfully chasing a breakaway. “I see you young Eric @ ZI”, he wrote. I had barely beaten him to the line in that last race, and he had later commented, “But there’s always next time. Keep up the good work Eric, and watch out for Old Andy trying to chase you down.” I figured Old Andy would be doing his best to beat me to the line this time!

Despite being mixed in with A riders, the pace for the lead-in and start of lap 1 wasn’t bad at all (thanks, double draft). I was averaging around 270W, but then one “L. Swatowski” (a rider using virtual power) attacked. I promptly messaged “zPower ranger attacks!” partly because it’s funny, but also in hopes of dissuading people from chasing.
But that didn’t work. The pack strung out, powerups flew, and the chase was on. And that’s when I began to feel the effects of being a bit sick.
As noted, I had already noticed that my HR was 5-10 bpm higher than it should have been for the given effort. But when the pace picked up for more than a few seconds, things just got suffery and miserable. My body didn’t want to perform.
At 14.6km I decided to pull the plug and drop from the front pack. I messaged the group to let them know I was dropping due to high HR/sickness. I also messaged “Good luck Old Andy! Stick it to the A’s!” He replied “Take care” and I dropped off the back and spun the pedals for a few minutes before signing off.
Old Andy: your 11th place finish in the Bs certainly beat my DNF. Chapeau!
Watch the Race
Takeaways
After the race I checked my numbers to make sure I wasn’t imagining things. Here’s my HR distribution for this race:

Here’s my HR distribution from a similar (but slightly harder) race effort one week later:

My weighted average power in the second race was 289W, while the race I quit due to sickness was only 273W. And yet, the sick race had me at threshold HR for 58.8% of the ride, while the race with higher power output only had me at threshold or above for 17.9%!
So I wasn’t imagining things.
I asked my cycling coach buddy Alan Dempsey for his thoughts on training while sick. He said:
There’s always a risk of myocarditis from doing that.
General rule of thumb is if it’s in your chest, don’t exercise.
If it’s not in your chest, max zone 1/2.
That’s pretty solid advice. He went on to say:
I look at it this way… you can’t work hard enough to gain fitness when you feel like shit. All you do is prolong the illness.
Adaptation from training is not dissimilar to an immune response. Damage >> repair.
So you’re not getting better. Riding easy might help maintain fitness while you’re sick, but still might extend the illness.
For me, recovering from sickness as quickly as possible is the best course for getting back to training healthy and staying fit. And when you’re sick that’s rest, fluids, and healthy eating.
Good stuff, Alan. It reminds me of this paper I read in the early days of the Covid lockdown when I was researching the links between our immune systems and exercise. The paper had a lot of good stuff, but two key takeaways were that “Acute exercise is an immune system adjuvant that improves defense activity and metabolic health” and “the best evidence supports that high exercise training workloads, competition events, and the associated physiological, metabolic, and psychological stress are linked to immune dysfunction, inflammation, oxidative stress, and muscle damage.”
Or to put it simply: low to mid-exertion exercise is an immune system booster, but high-exertion exercise stresses the immune system so it doesn’t function as well.
The common rule in cycling is, “If it’s above your neck, you can ride. If it’s below the neck, rest.” Not a bad rule, but I would expand that rule a bit and say if your heart rate is elevated, or you’re feeling sick at all, keep it at zone 1-2. Don’t stress the immune system that’s already working hard to make you whole again.
Your Thoughts
Have you ever ended a race or workout due to high HR from sickness? What are your personal practices when it comes to riding while you’re sick? Share below!
I’ve already been sick and I know my heart was going to come out of my mouth. I went to the doctor and did several tests but after recovering from covid and losing more than 10kg and a lot of watts I came back…
Great post. That’s one of the great things about Zwift: Alyou can just bail if you’re not feeling up to it. I have suffered through workouts IRL where I was coming down with something but was too stubborn to admit it. I think it always takes longer to heal when your body is trying to fight something off, and then you overload it by pushing a workout or a race. Much better to just take the rest.
Excellent post showing that we are all human after all, and subjected to the elements and environmental conditions. Being sick is also a natural response from the body alerting us of the need to slow down the – life pace. I too have had many instances where not feeling so good and pushing it through, to only later realized that it was a mistake and paid for it for longer recovery than necessary.
Very good post. I think this is all the more relevant as you age.
theres always a ZP who ruins a race thinking they are legit
Always! That’s why I’m a fan of Zwift’s hardware enforcement. Race organizers should require people to have a smart trainer or power meter in order to race, IMO.
Yeah for sure. Cheating is rampant on Zwift, always has been, and honestly the new “race” mode or whatever Wahoo calls it is honestly a client side cheat, because only a select few (pay to play) riders will have access to it. One thing I am sure of, is that ALL companies involved in Esports don’t care at all about cheating. I have been a server admin for AAA FPS games for over 20 years and what I have seen people do to win is disgusting And now, since games like COD have take over all the servers, they simply… Read more »
If I’m sick the only rides I do are easy spins just enough to get a sweat going. This body temperature elevation + sweat response is enough to maintain plasma volume (according to the science I’ve read…) so that when I’m better again I don’t have to get that memo to my body again. This is like a 5-10 minute thing, easy. Otherwise if you do not ride for 2-3 days your body ejects the “excess plasma” (no need to sweat, why not…) and the first 2 days back are all temp / HR dysregulated because you have to build… Read more »
I cut out most exercise when I’m ill, even if it’s just a cold. My problem is always when to get back to it: recommendations suggest no more than 10% increase in activity each week which is hard to follow when you’ve done none at all last week!
Also, I often get a mild cough for weeks after a mild cold, so is this a “chesty” issue which means I should stay off exercise? Your stay in zone 1-2 recommendation is a good compromise.
The pandemic has made me a bit more cautious about doing z3+ when I feel like I’m coming down with a lurgy, but sometimes heart rules head and I to to exercise anyway… Just like doing last week’s zone 2 Tiny Races! I was aware I was struggling a bit more than normal from around half way through race 1, race results and my more my own performance were a bit disappointing, but it was only in the pen for the final race I seriously considered calling it a day. Did it anyway, of course, to complete the quartet. But… Read more »
man i would kill to be at 135-140 bpm with Coco 😀
get well soon
highlights an interesting topic: typically athletes are taught or learn to “tune-out” what their body is telling them and just “crack on”. however outside of competitive sport, this behaviour can have disastorous consequences..! so instead we should be teaching people (especially athletes) that it is important to listen to what your body is trying to tell you and react to it accordingly.
me: “im feeling tired and sore, my knees are hurting – just plod and cruise with some slower guys”
actual: starts and gets triggered by the 1 guy who wants to keep riding hard off the front, thinking we all should die for 100th place… so i get into a pissing contest to teach him a lesson :/
I see you struggled again last night Eric. Take it easy fella.
We disregard heart rate data at our own peril. Really, what’s the point of “toughing it out” if we extend an illness or (worse) damage our cardiovascular system? Sometimes we don’t know what we had until it’s gone.
Just have to say it… If you are sick/injured REST. You aren’t impressing anyone 10 years down the road. So much wisdom behind that. Worst case I have ever had by pushing through was the criterium state championships (or something like that – 30 years ago) back in the 80’s when I raced. I pushed through a “sickness”, turned out to be influenza, the real deal, and I not only missed the finals, but I missed 2 weeks of classes in university which almost caused me to not make it through the semester. I almost died man. 2nd worst/stupid thing… Read more »