Blood Test has wiped me out!

Hi Brains Trust, this morning I had a fasted blood test as part of a regular checkup.
All went fine, ate a normal breakfast albeit 2 hours later than normal. Normal lunch, and nothing out of the ordinary

4.5hours post test, I did a 1 hour endurance ride on the trainer to avoid any intensity. 45 minutes in and I was on struggle street. HR through the roof and struggling to hold any power, so dropped the effort to zone 1 and finished the hour

Now, post ride, I’m ruined… feel like I did a 6 hour+ ride, light headed, hot/cold flushes, dizzy when I stand and my legs are toast

Tell me this is just a case of over doing it. I thought leaving the intensity aside would be enough, but is it?
Anyone been through this?

Blood test wouldn’t have done that. The amount of blood taken is minimal. Even the fasted bit ahead of the blood test should not have done much unless your glycogen stores were already depleted.


Sounds to me like you may have a bug…

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I’m leaning that way as well… :face_with_symbols_over_mouth:

Tbh, this is a bit familiar. I failed a hard interval session on Wednesday, and on Thursday started feeling below par. By Friday, I had mild flu symptoms with RHR +20 bpm.

By Monday, RHR was down to +10 and I felt 80% better, so I tried an easy ride: HR was 10-15 beats elevated for Z2 power, and I started feeling a bit crappy after 25 minutes so I ended the session after half an hour. Yesterday, felt 90%, and RHR +5-8, so I did an hour on Zwift; HR was 5-10 bpm elevated for Z2, and heavy legs after an hour. I’m taking today off and will try another Z2 hour-75 minutes tomorrow.

I suspect it’ll be next week before I’m firing on all cylinders, and you may be the same…

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Throwing in another opinion that you might have a bug. Weirdly similar, I had a fasted morning/blood test last week, ate about 2 hours later than usual, and hit a hard running workout 5 hours later. Felt totally normal during and after, and managed some big bike volume the following days, all normal.

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I’ve been tracking my HRV for about 6 months and my lowest score so far by a long shot was after a stressful doctor’s appointment. I always get a little stressed going to the doctor even when everything is fine but this time no invasive tests but for the first time in my life had to discuss something potentially serious.

Maybe it was not the blood test but stress?

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That’s not from a simple blood test.

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I had a blood test yesterday (6ml blood taken I think. No more than 10ml anyway) and 9 hours later I attempted Goode outside. I powered through but the threshold efforts felt like Vo2 and the Vo2 efforts i couldn’t hit at the target power…

Today I tried Truuli-1 and couldn’t hold 3min threshold! I could only find research on red blood cell recovery from a full blood donation. I have an A stage race staring in 6 days. Has anyone raced a week after a blood test?

I’m hoping my performance will recover in a few days because it wasn’t that much blood but it’d be great if someone could put my mind at ease if you’ve been through it :sweat_smile:

10ml of blood would be approx 0.2% of your total blood volume (assuming 5l blood volume, per Blood volume - Wikipedia ).

It’s unlikely that the loss of blood itself has anything to do with how your workout felt. How were you feeling otherwise? Were you worried about the test, or the results you will get from it? That’s more likely to account for your performance on the bike than the purely physiological effect.


Thanks. Yeah there’s other factors I should probably consider like only 4 hours of sleep the night before and fasting prior to the blood test and not eating for a few hours after. Also the stress of getting a PCR test, waiting for the results, and everything else ahead of traveling to my home country ahead of nationals.

Lots of thoughts here and I’ve had similar issues. They lasted about two weeks+.

At the time I had to take some strong painkiller for a neck spasm injury, that elevated my resting HR, then I went into abit of man-flu symptoms (not covid) which also elevated my HR further, it never really had chance to come down. That was followed up by my second COVID jab and finally some pretty stressful anxious moment at work and home. All in all I got into a pretty vicious and deep mind bog over it all and the whole thing was a terrible experience. Thankfully now I feel it was just quite a few body blows over an unlucky period of weeks. All in all my RHR was about 20bpm higher which meant I hit my ‘ceiling’ a lot earlier than I normally would. I’d try my best not to worry about it. I think that was the worst thing I did. Some of us are just born fretters.