A lot of athletes will not give blood because they fear it will affect their performance. I found a good article in Triathlete Magazine about blood donations. The doctor notes that it can take anywhere from two days to a month to get back to optimal performance after a blood donation. The first time that I gave blood (in July), I did experience some sluggishness on long bike rides (over three hours) in the intense Alabama heat. However, while I suspect that the blood donation may have been the cause, it could have been a number of other factors such as diet, stress or being at a certain point in my menstrual cycle.

Since I haven't planned to race in the next month or so, I gave blood again today. I didn't eat much for breakfast this morning and that didn't cross my mind as I sat down in the chair. After they finished sealing up the baggie, I started feeling dizzy. Next thing I know, they have me reclined in the chair, placed ice packs on my stomach, chest, neck and head, and they are trying to force feed me grape juice. My blood sugar had tanked. I couldn't breathe deeply and I was burning up. After a few minutes, I started to feel better again. I drank juice, ate cookies, and then went back to work.

If that is what 'bonking' at a race feels like, count me out. It is very unpleasant.