Miguel Indurain--"Big Mig"--the Basque Spaniard who won five consecutive Tours de France in the early '90s, is by the standard of physical prowess one of the top few athletes in history. This I judge solely by his victories and an analysis of his capacities (the following is a quote from Wikipedia):
According to the University of Ferrara, who conducted tests on Indurain, his strength came from his body's superior physiology. His blood took 7 litres of oxygen around his body per minute, compared to 3–4 litres for an ordinary person and 5–6 litres for fellow riders. His cardiac output was 50 litres a minute; a fit amateur cyclist's is about 25 litres. Indurain's lung capacity was 7.8 litres, compared to an average of 6 litres. His resting pulse was as low as 28 BPM, compared to an average 60–72 bpm, which meant his heart would be less strained in the tough mountain stages.