I have not heard of many complaints from bodybuilders but I have heard many runners say it lowers their energy levels. When you give blood, you lose the oxygen-carrying hemoglobin in those red blood cells, and as a result you run slower. It takes about 5 weeks to fully restore the hemoglobin. But for bodybuilders on anabolics its another story. Anabolics usually thicken the blood or increase hemoglobin levels so giving blood is a way to thin the blood so it can pump thru the body better and reduce the chance of blood clots.