Giving blood is a great way to help others, but what happens when you show up to your next workout low on blood? Some aspects of fitness bounce back quickly, but you might want to put off any races or competitions for a few weeks.
Photo by Tom
Blood donation groups advise against heavy exercise the same day you donate, to avoid reopening the needle wound and because you may feel dizzy or faint from low blood pressure.
Plasma, the watery part of your blood, will return to normal levels within a few days. (You can help this happen faster by drinking lots of fluids, not just at the blood drive but for the next day or two). A study of cyclists who donated only the plasma portion of their blood showed that they didn't last as long on an endurance ride the same day they donated, but were back to normal two days later.
Red blood cells take longer to regenerate. These cells carry oxygen from your lungs to your muscles, so when you're low on red cells, aerobic performance suffers. The same study of cyclists also looked at the effects of donating whole blood on VO2max, a measure of how much oxygen their body could use at one time. It's one measure of aerobic fitness. They found that the cyclists' VO2max dropped by 15% on the day of donation, but by a week later was only 7% below normal.
How long does the effect last? One study that used recreational athletes found that they were exercising at normal levels three weeks after donation. Another, done more recently, showed that the men in the study (who all donated blood on a regular basis) were back to their pre-donation fitness level by two weeks, even though tests showed that their red cells were still a little low. That result led the authors to recommend waiting two weeks or more before you expect your best performance. The exact amount of time will probably vary from person to person.
If you race or compete regularly, your best bet may be to donate blood after a race, when you're taking a few days or weeks of recovery, and when you know your next competition is several weeks away.