Forget carbon-fibre plates in your shoes. Imagine how many miles per week you could train if you had carbon-fibre LEGS. You'd never be injured and the blood required in the fleshy part of your body would be less than before so the heart would not have to work as hard. Once we have the technology and approval by the governing bodies of the sport it will become a reality! Imagine a 60 year old over-the-hill Kipchoge sawing off his legs in pursuit of the 1:50 barrier!
you have never heard of the paralympics? carbon legs have been a thing for a long time.
I listened to a podcast about Oscar Pistorius, some scientists had determined that without losing his legs and running on those carbon blades, he would be at best an averagely fast runner i.e. nowhere near national or world class standard. They said that at the time he was competing there were people questioning whether the blades' bounce provided a competitive advantage against athletes with both legs or 1 leg. In the end they said the bounce of the blade made little difference and it was the fact that his legs were significantly lighter that gave him an unfair advantage - his leg turnover was able to be much faster than a typical world class runner because he had to move much less mass forward each stride.
"One of the biggest points of contention is limb-repositioning time. The average elite male sprinter moves his leg from back to front in 0.37 second. The five most recent world record holders in the 100-meter dash averaged 0.34 second. Pistorius swings his leg in 0.28 second, largely because his Cheetah's are lighter than a regular human leg. Pistorius's rivals are swinging a lower leg that weighs about 5.7 kilograms, whereas his lower leg only weighs 2.4 kilograms."