For access to all of our training, gear, and race coverage, plus exclusive training plans, FinisherPix photos, event discounts, and GPS apps, sign up for Outside+.
Blood donation remains one of the most selfless and altruistic things that a person can do. Despite the myriad advances by drug companies over the years, no drugs have ever been developed that come close to accomplishing what our own blood can do. Consequently, we remain dependent on the generosity of donors who take a half-hour or so to give up a pint of this incredibly valuable, lifesaving fluid.
But that dependence makes the availability of this valuable resource very precarious. In January of 2022, in response to plummeting donations in the face of surging COVID infections as a result of the Omicron surge, the Red Cross issued its first-ever “Blood Crisis” in which the organization desperately appealed for donors to help shore up critically low supplies. Fortunately, the crisis was short-lived as donors responded and blood banks were able to achieve low but sustainable levels in short order.
However, the supply of blood is continuously under threat. Even today, multiple blood banks across the country are reporting shortages, from New Jersey to Kentucky and California. Because blood has a limited shelf life and the demand is unpredictable, any change in the number of donors can dramatically impact supply. At any given time in the United States, as many as one in five medical centers are operating with a one-day supply of blood products, putting patients at significant risk.
So why is blood such an important resource for medical care? Blood is made up of several components and serves many purposes. After donation, whole blood is separated into its component parts so that each can be used for recipients who have specific needs.
Blood donation, explained
Red blood cells containing the oxygen carrying molecule hemoglobin are separated and made into a unit of PRBC-packed red blood cells, so that they can be reconstituted with saline and infused into patients with anemia for any number of reasons. Trauma victims, cancer patients, and patients undergoing major operations are just some examples of the people who benefit from PRBC. Platelets are important for blood clotting and various conditions can drop patient platelet counts dangerously low in which case bleeding can become an issue. Platelet transfusions may be life saving for them. Finally, the protein-rich plasma has many possible roles and can be given to patients with various types of ailments including autoimmune processes like Guillain Barré syndrome or Myasthenia Gravis or more recently, for patients with severe COVID-19-related illness.
Each year, 45 million units of blood are donated at blood banks throughout the western world, according to the American Red Cross. However, these donations are made by 4% only of the population. There are myriad reasons for why more people don’t give blood, from fear of needles, to a lack of knowledge of the need and benefits of donating and for some, a perception that donating blood can have detrimental effects such as exposing the donor to the risk of infection (it does not).
But for endurance athletes training for a race, a common concern is how donating blood will affect their ability to train and race. When is is safe to exercise after giving blood and what should you expect as far as your performance?
How does donating blood affect athletic performance?
Endurance athletes have long known that receiving blood transfusions may enhance exercise performance by increasing hemoglobin concentration and allowing for improved oxygen delivery to the cells. So the logic stands that many athletes wonder if donating blood can have the opposite effect: Can lowering hemoglobin concentration by donating blood negatively impact exercise performance? Fortunately, there is a reasonable body of evidence on the subject that can help athletes make an educated decision on this important question.
After a typical blood donation, hemoglobin levels do indeed predictably decrease by an average of 7 percent and remain depressed for at least 14 days after donation. By then, they have recovered by about half, to a 4 percent decrease from pre-donation levels, according to a 2017 study in Transfusion. Hematocrit, or the measure of what percentage of blood volume is made up of red blood cells, also decreases for the first few days after a donation. Hematocrit also decreases by 5 percent 48 hours after donation, recovers within two weeks after the donation. This is because the new cells that have been synthesized in that two-week period contain less hemoglobin than more mature cells. As a result, the hematocrit recovers more quickly than the hemoglobin concentration.
Because hemoglobin is needed for carrying oxygen to tissues in the body, the decrease in hemoglobin seen with blood donation is associated with a decrease in oxygen-carrying capacity and delivery, accounting for a measurable 7 percent decrease in VO2 max in the 24-48 hours after donation. Interestingly, this decrease completely disappears by day three, suggesting that blood volume has re-expanded by that point and increases in heart rate likely compensate for the decreased hemoglobin to restore oxygen delivery to normal. Because VO2 max is a measure of oxygen utilization by peripheral tissues, if oxygen delivery is restored to near-normal levels by the third day after a donation, then it makes sense that VO2 max would recover, as cellular metabolism is unaffected by hemoglobin levels alone.
Along with the decrease in VO2 max, measured maximal exercise capacity as well as time to exhaustion when performing at threshold also decreases by about 10 percent after a blood donation, then fully recovers by one week. Submaximal efforts have never effectively been studied, so no clear conclusions can be made about efforts in that range after blood donation.
Taken together, these findings suggest that blood donation is indeed associated with a measurable decrease in exercise performance, principally at the highest levels of exertion. This effect is maximal for the first two days after a donation, and has disappeared by fourteen days after donation.
When can I exercise after donating blood?
Clearly, blood donation is compatible with endurance training. Athletes need only to incorporate such donations into their schedule so that they do not have high-intensity training for several days to a week after a donation, and certainly should not donate within two weeks of a race.
The satisfaction gained from the knowledge of having helped others in this way should be more than sufficient motivation to arrange one’s schedule to make this possible. Please donate and do your part to help save a life.