Reasons for a difficult run: As I think I may... - Bridge to 10K

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Reasons for a difficult run

โ€ข21 Replies

As I think I may already have mentioned (!!!), I did my first ever 10k run yesterday, and it was hard! I know there are many reasons some runs are like that, so wasn't too worried.

When I checked my stats afterwards I noticed that my heart rate was at least 15 bpm higher than it usually is, for the whole run (glad I didn't check whilst I was running - it might have put me off). But I'd made it home and was still alive, so again, not too worried.

Then just before I went to bed I remembered that I'd had a flu jab two days before my run. I've had no side effects from it so had forgotten all about it. But now I'm wondering if my body was so busy creating antibodies it had to work super hard to keep me running.

Any thoughts anyone?

And if that's the case, thought this might be useful for others to know ๐Ÿ˜Š

21 Replies

I do not think so Tartancat, I had my flu jag last Wednesday afternoon and on Thursday morning I ran a 5k, yes like you I was a bit tired bit I don't think that flu jag made any difference.

TartancatGraduate10 in reply to AlMorr

I know when you give blood they advise against strenuous exercise, but nothing was said when i had the injection, so I'm guessing it shouldn't usually be a problem. I just wondered .....


Well your immune system would certainly be kicking in & doing its job. Who knows! ๐Ÿ˜ƒ


Doesnโ€™t the jab give you a mild case of the virus? Or am I making that up? If it does, itโ€™s possible you could have been subconsciously under the weather. ๐Ÿคง๐Ÿคง๐Ÿคง

But hey, TC, only one way to find out .... run 10k again next week and compare your stats! ๐Ÿ‘๐Ÿ‘๐Ÿ˜€๐Ÿ˜€


I had a terrible feeling I might have to do that!

The virus isn't live so it can't give you any flu symptoms, it just gets your body ready to recognise the real thing if it comes along (not very scientifically put).

Like you say, I'll have to do it again to compare!

cheekychipmunksGraduate10 in reply to Tartancat

Well if you want some ๐ŸŒ๐ŸŒ you know who to ask! ๐Ÿ˜…


It may be coincidence but I had exactly the same experience after my flu jab recently and posted the same question. Average heart beat was way up on normal and I was shattered at the end of the run. So may be something in it, but different people may react in different ways. Congrats on the 10k!!!๐Ÿ‘๐Ÿ‘๐Ÿ‘

TartancatGraduate10 in reply to Beachcomber66

Thanks Beachcomber, you're right, it does affect us all differently.

If I have the jab again next year I'll plan a short run after, not the longest one of my life so far!

Beachcomber66Graduate10 in reply to Tartancat

It was a one of the shorter run on the plan, 5k from memory, that I had trouble with. I am going to leave three days or so before running after my next jab. Of course the vaccine is different from year to year too, so maybe after affects will be different too!

TartancatGraduate10 in reply to Beachcomber66

Good point!

Gran4zGraduate10 in reply to Tartancat

Iโ€™m getting my jab next Saturday, so will experiment. I was thinking of trying for the elusive 10k - mind you Iโ€™m just tired all the time anyway ๐Ÿ˜‰๐Ÿ˜ด๐Ÿ˜ƒ.

Actually strangely enough running does weaken the immune system, thatโ€™s why apparently itโ€™s better not to run hard when youโ€™re feeling under the weather. Mind you I can tell myself I feel rough, still go for a run, and feel so much better for it.

Anyway I digress, so maybe adding in an extra insult to the immune system might just be enough to skew our internal workings. Oops Iโ€™ve wittered on, apologies ๐Ÿ™ƒ๐ŸŒป

TartancatGraduate10 in reply to Gran4z

No apology needed! Can't wait to hear how you get on with your 10k. Best of luck ๐Ÿ˜


Maybe it was just hard because it was your first 10km?! Who cares if it was hard, you did it. And with more running at longer distances, it can only get less hard, right? ๐Ÿ˜˜

TartancatGraduate10 in reply to Sadie-runs

I'm sure it being my first 10k has a lot to do with it, and I look forward to it getting easier!

It was the raised heart rate that got me wondering really. I know fitbit isn't hugely accurate and I don't take a lot of notice of it in the main. It usually goes sky high at the beginning then settles down, but yesterday it stayed elevated beyond the norm.

The main thing is, I did it, and I'm still alive to tell the tale (and bask in the glory)!

Like I say, I'm not worried, just curious ๐Ÿ˜ฎ

ArthurJGGraduate10 in reply to Tartancat

Fitbit - and indeed ALL wrist worn heart rate monitors that use optical technology, regardless of brand, yes you too Garmin - are not only approximate, which would be fine as they are not medical devices, but also known to be particularly unreliable under conditions of strenuous exercise. A known issue is that when you are running, or indeed walking, they sometimes measure your cadence (strides per minute) instead of your heart rate. So if you know roughly how many strides per minute you typically run, and if the elevated reading was somewhere around that figure, it may be that the reading wasn't your heart rate at all.

I'm not qualified to comment on the flu virus but an online search suggests that if you feel OK then cardio exercise is actually beneficial. The NHS website has no warning against it and points out that it's not a live virus so can't itself give you flu: if people get flu like symptoms afterwards it's a coincidence: they've either got another virus that isn't the flu or they caught flu before being vaccinated. So if people feel unwell after the vaccine then they were likely going to be unwell anyway and no, they shouldn't run till they feel better. We never run when actually ill, if we have any sense. But you weren't ill so your run has done you no harm and from what I've read the cardio may even have increased the effectiveness of your flu jab.

TartancatGraduate10 in reply to ArthurJG

Thanks Arthur, really interesting about heart rate and cadence getting muddled up, that may be the issue here.

I know wrist hr monitors don't work well when you sweat (go figure!), so I'm always a bit dubious. To be honest, my performance really doesn't warrant needing to monitor my heart rate! But I do love stats (though what do they say about lies, damned lies and statistics?)!!

ArthurJGGraduate10 in reply to Tartancat

Like all stats they're useful if you understand them. I've had a couple of 20 minute walks that Strava said were far more strenuous than when I ran my PB at 5k. The same walk on other days hardly registers. Now I know it's because my Fitbit was sensor was oscillating in time to my feet and not my heart, I know I can disregard those two figures and look instead at the other times I've done the same walk.

ArthurJGGraduate10 in reply to Tartancat

I once heard one politician accuse another of 'using statistics like a drunk man uses a lamppost - for support, not illumination' :)

TartancatGraduate10 in reply to ArthurJG

Love it, and that probably sums up most politicians!


I used to exercise with a polar watch and chest strap, it had a warm up / assessment function at the start of each session where it would monitor how your heart rate responded to increasing exercise intensity and then set your heart rate zones for that session accordingly. I noticed that the limits for each zone would drop significantly when I had a cold and spookily, the watch seemed to know when I was coming down with a bug 24 hours before I did, dropping my upper limits as it would for a full-blown head cold, even though I felt fine.

Iโ€™m not a Dr but it seems plausible to me that your immune system could be ramping up to deal with what it perceives to be a virus so your body is trying to conserve as much energy as it can to deal with that threat.

Do you know if your resting heart rate increased after your flu jab too?

Fingers crossed ๐Ÿคž your next 10k will be a breeze ๐Ÿ˜

TartancatGraduate10 in reply to Teri73

Wow, spooky Polar watch! To be honest, according to Fitbit my resting heart rate hasn't increased. It did take longer to recover after the run, but as I'd run further than ever before I'd expect that. The word I'd use is "inconclusive"!

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