I am going to attempt to clarify things just a touch but will likely muddy things further so forgive me. Then, I'll answer the OP question... O- is the universal donor, period. Final.
But...
O+ is the universal donor for MEN. The reason for this is that O- is rarer than O+ and we can't risk sensitizing Rh- women with Rh+ blood.
So when a trauma patient comes in to my ED and we need blood right away we call the blood bank and ask for male or female blood. If it's a male we get the more available O+ blood because giving an O- man O+ is not dangerous and there are no downstream effects. But if a woman comes in we call for female blood and that is O- because sensitizing a woman to Rh can lead to significant complications of pregnancy and THAT my friends is the subject for a whole other lecture. I hope this makes sense?
OK, to the original question about donation and training...
I wrote about this for Triathlete Magazine many years ago. Here is an excerpt from that piece: "Donating a pint of blood, (450cc) results in a total body depletion of about 10% of your total blood volume. Of that, only about 160cc are red blood cells. The fluid component, 290cc, is replaced within hours but the red blood cell replacement takes about two months, (which is why you may not donate more often than every two months). What then are any lasting effects of this red blood cell loss? Oxygen delivery to the tissues is dependent on both your respiratory and circulatory systems. It can be calculated by determining the concentration of inspired oxygen, the hemoglobin concentration, the percentage of hemoglobin that is saturated with oxygen and the cardiac output, (the amount of blood pumped by the heart in 60 seconds). If the other factors remain unchanged, a drop in hemoglobin concentration associated with donating blood will drop your oxygen delivery by 10%. However, under resting conditions, the oxygen delivery at this decreased rate still far outpaces the demand. When exercising you increase your cardiac output in order to compensate for the higher demand that your muscles are making for oxygen. At moderate levels of exercise, the supply will still outpace the demand even with the loss of hemoglobin. At higher levels of exertion however, the demand will outpace the supply at a heart rate that is approximately 5-10% lower than your usual anaerobic threshold. For example, if your metabolism becomes anaerobic at a heart rate of 170, then after donating blood you will become anaerobic at a heart rate of somewhere between 157 and 164. This value will be in flux of course because your hemoglobin level will be rising slowly each day after your donation. So the most effect will be felt only in the first few days."
I hope this helps!
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