Note that Riis's results were before the 50% hematocrit limit (he was nicknamed "Mr 60%'). Hematocrit is a measure of the hemoglobin content, or oxygen carrying

Note that Riis's results were before the 50% hematocrit limit (he was nicknamed "Mr 60%'). Hematocrit is a measure of the hemoglobin content, or oxygen carrying capacity, of the blood. So, even though later cyclists were also blood doping or using EPO, they have been limited to a 50% hematocrit, and that may explain why Riis's power output has not been matched.