Dear Dr. Roach: I am a fit 54-year-old male who bicycles a lot. I donate blood as often as I’m allowed. After donating, my legs feel more fatigued when I ride, and I’m not as strong. How long can I use my blood donation as an “excuse” for lacking strength?
Dear A.R.: What ultimately determines how much work your legs can do is the amount of oxygen the muscles are able to get, once you have achieved a high level of muscular fitness. The amount of red blood cells in your blood and the amount of blood your heart can pump are the limiting factors for oxygen delivery in a healthy person.
So, for a given degree of cardiovascular fitness, your ability to go fast and climb hills is directly influenced by how many red blood cells you have. That’s why elite cyclists sometimes used to get blood transfusions before a race.
An extra unit of blood might make only a 3-percent difference, but the difference between the winner of the Tour de France and the last-place finisher is right around 3 percent.
Unfortunately, too many red blood cells increases the risk for stroke and heart attack, and several amateur and professional cyclists have died as a complication of too much blood transfused or its more modern equivalent, the hormone erythropoietin, which causes the body to make more of its own blood. Losing blood, from bleeding or donation, consequently reduces performance.
The plasma (fluid and proteins) is made up within 24 hours after donating blood, but it takes four to six weeks to regain the blood cells. Donating a unit of blood can save up to three lives.
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