I intend to give blood at some point this week at my local community centre.

  • How much of a difference is this going to make to the effort required to keep up my usual pace? Or will the difference be negligible?

  • How long will any potential effects take to wear off?

I know professional cyclists have in the past (of course this is completely eradicated nowadays...) increased their blood volume to give them an advantage over the rest of the peloton. Can I infer that a lower amount of blood will have the opposite effect?

I commute ~16km most days and usually go out for a longer ride at the weekend so I'm fairly used to cycling intermediate distances.

  • 4
    I recall 20-30 years ago cycling to work, giving blood, then cycling home that evening (12 miles one way over "gently rolling" terrain). I got light-headed and had to stop and rest, then take it easy the rest of the way home. Was fine the next day. (Drinking plenty of extra fluid will probably help.) May 27, 2015 at 10:55
  • I'd ask a medical doctor as this can have important impact on your personal health.
    – Max
    May 27, 2015 at 13:44
  • @Max I've given blood many times before so I'm not worried about the health consequences
    – kaybee99
    May 27, 2015 at 14:36
  • 1
    Anecdotally, I've only done this once, and it really wore me out and made me light-headed for a few-mile long ride home.
    – Milo P
    May 27, 2015 at 15:30
  • Another anecdote to contribute - one morning, I noticed I was really struggling to get up my normal 11-flight stair climb to the office. I was confused... until I realized I'd donated blood the previous day.
    – mskfisher
    May 27, 2015 at 21:04

5 Answers 5


Depends on exercise intensity. In a day or two you can return to your normal/moderate exercise. A complete recovery of oxygen delivery can take as much as 3/4 weeks.

This means a professional athlete should be careful because he will loose performance, but us normal human beings can carry our normal daily lives.

You can read more complete answerers given by pro-triathletes and physicians, here. You can also find scientific references to support their claims, if you really want to get deep into the subject (I didn't).

Curiously, they state there isn't much research in the topic. I assume pro athletes just don't take the chances, and to normal people giving blood has a neglectable impact in our daily life. If you helped another human being, who cares if you take more 5 seconds to do the 10 miles from your house to your local pub, right? :)

  • Excellent link. Seems to suggest more studies are required to fully ascertain the true effects. Whatever the effects, as you say, its certainly worth it!
    – kaybee99
    May 28, 2015 at 8:13
  • Pro athletes obviously go the other direction -- they ADD blood (blood doping) before a competition. May 28, 2015 at 11:01
  • Yes, as I mentioned in my question. I've marked this as correct as I feel it answers my question most comprehensively (with fantastic references!). Thanks to all contributors.
    – kaybee99
    May 28, 2015 at 13:46
  • 1
    Personally I found that it was closer to an extra 5 minutes (again not a life changing amount of time). But the corollary to that, is that I found when I then replaced the fluids lost at the pub, my performace drpped mcuh moa!
    – Aron
    May 28, 2015 at 16:47

If you are riding near your aerobic limit you'll definitely discover that you've lost aerobic capacity during the next 12-24 hours. It can take that long to replace the red blood cells you've lost.

Since a blood donation is about 10% of your blood capacity, your aerobic capacity will be down by 10%

I wrote the rest of this before I saw your comment that you've given blood many times. I'll leave it in the post for future readers.

Initially, the main issue is blood pressure. Plenty of fluids are recommended as soon as you finish giving blood. It only takes an hour or two to overcome this.

The conservative advice would be to avoid cycling for the next 24 hours. Until you know how you react to giving blood this is what I recommend. After giving blood a few times you could try riding gently and see what happens. I would still avoid riding on roads in traffic.

Edit: see also the link provided in the answer by @super.

  • 1
    I don't think the drop in aerobic capacity will be that much for 2 reasons: personal experience as measured by gym equipment and the fact that you in practice have a reserve of blood in the spleen of ~1/2 the donated amount. However I find that I get thirsty during even mild exercise even the day after giving blood, despite drinking a lot immediately -- so carry (extra) drinks in case you get the same.
    – Chris H
    May 27, 2015 at 12:17
  • 4
    @ChrisH Certainly YMMV. When I used to donate I was playing competitive squash. I soon learned that I could play or donate, not both on the same day.
    – andy256
    May 27, 2015 at 12:19
  • This is incorrect. RBCs take longer to replace than 12-24 hours. A clue to how long it would take to replace the RBCs is how long health officials recommend/mandate between donations. Finally, it's more complex than your answer states, as your spleen (assuming you still have one) will partially replace part of the RBCs lost.
    – Aron
    May 28, 2015 at 3:56
  • @Aron The link provided by super's answer supports your point on the RBC replacement time, but then says not much research has been done. In my experience 24 hours had me back to full performance. But I think the main point is that a rider should take extra care for the first 24 hours.
    – andy256
    May 28, 2015 at 4:03
  • Your general point about the 24h bit is not in contention (at least from me). The cause is (IMO) more likely to be extended dehydration. Given the lack of research on more fundamental related questions I wouldn't expect there to be anything significant on how efficiently the lost blood volume can be made up by drinking. Someone should compare the effect of giving a unit of saline via a drip immediately after donating. (also @Aron)
    – Chris H
    May 28, 2015 at 12:43

I used to cycle 8 miles each way on my way into central London, before I moved. I also used to give blood before moving to a country where they prefer not to accept mad cow blood. So there you go.

I found that on a good day I used to be able to cycle into work in about 40-45min.

I also found that the days immediately after a donation I would take 45-50minutes approximately to make the same trip.

I also found that it would take approximately a month for me to recover my pb speed, which matched quite well worth when I would be due to donate again.

Overall I found it definitely does make a huge impact on performance. On the other hand that same performance change actually made very little difference to my commute.


It's harder to cycle for about a month, or how long the vampires wait before bleeding you again.

It's also very manageable for commutes, but you will definitely not be hitting your pb.

  • 1
    I suspect there's a connection between your recovery time and how often you're allowed to donate :)
    – Móż
    Oct 31, 2016 at 0:55
  • @Móż I've found that the in between donation periods tend to be the between "half life" and the "mean lifetime" for erythrocytes depending on the location. Since erythrocytes will be the main determining factor for medium term performance loss, policy is consistent with biology.
    – Aron
    Oct 31, 2016 at 2:03

I cycled up Box Hill today in 8.30 minutes after giving blood last Friday. My fastest time this year was 6.40 and my slowest time when trying was 7.26 at the beginning of the year when I wasn't fit. I would never have believed it would make that much difference but I felt light head headed and if I had tried any harder I think I might have fainted. I just didn't seem to be able to get any air in and I was breathing really hard for the effort. I have low blood pressure anyway so I wonder if that made any difference too. As soon as I stopped cycling I felt fine and going along on the flat didn't feel too bad. It wouldn't put me off giving blood but if I was planning to race I think I would give it about 6 weeks. The same thing happened a few years ago when I gave blood and did a 10km about 2 weeks later. I thought maybe I was a bit under the weather but I had the same feeling as today and was about 2 minutes slower than I would usually be.

  • Was it Box Hill in Surrey, or Australia, or Scotland, or Montana?
    – Criggie
    Oct 30, 2016 at 23:26

Yes, it will affect you, but I doubt you'll notice the difference.

Some people do feel fait afterwards, but I believe this is related to blood pressure rather than red blood cell count and your body can replace the fluid relatively quickly, so have a cup of tea and a chat before you leave and you should be ok.

When I was giving regularly, they asked if you were going to be operating heavy machinery later that day. If you tick that they'll ask you about it and give you better advice than someone anonymous on the internet...

  • I am aware of the list of questions asking whether you will be operating heavy machinery, flying planes etc. My question wasn't about safety, rather about the difference in performance. I've given blood enough times and been riding for long enough to know I'm not going to fall of my bike!
    – kaybee99
    May 27, 2015 at 10:28
  • For me, I cannot say that I have actually noticed any significant difference. I am in average good shape and I do not stop going to the gym or go out dancing just because I have been giving blood the same day.
    – hlovdal
    May 28, 2015 at 7:37

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.