Roger Bannister achieved world fame in 1954 at the age of 25 by becoming the first person to break 4 minutes for the mile. What many people don't know about Bannister is that he was a medical student at the time and was already carrying out experiments, using himself and friends as subjects, to investigate the effects of inhaling oxygen enriched air on the physiological response to maximum exercise.
I read an interesting article describing the conditions of these experiments on inclined treadmills in the 1950's.
You had to breath from great gasbags and they had blood guns which sprang a blade into your finger to measure lactic acid levels as you labored on. You poured sweat, your spine turned to rubber, and driving up the incline there was the most extraordinary effect on your chin and knees meeting in front of you. Near the end, there was blood all over, and when you broke, you staggered and rolled off onto a mattress, trying to hit the off switch as you went down. Roger himself ran to breaking point on at least 11 occasions. Compared to that, the 4-minute mile was like a day off.
Sir Roger Bannister went on to become an eminent neurologist and retired in 2001. He will be 80 next year. The current mile record for men is 3:43 set by Hicham El Guerrouj of Morocco and it has stood since 1999.