You can find many people that their body built is similar to the elite sprinters- athletic big muscles look low fat etc. however, they are not even close to the elite sprinter's speed. Instead of 10 sec/100m, they would do 15-14 sec 100m. So physically wise what differs them? Is it something internal? Organs ect..?
And same goes for the long distance runners- people with the same outside look, yet if trained they would not even be close to the elite times? So what differs them? Internal organs? Bigger heart/lungs?
And third question- both sprinters and long distance runners have speed- but why would someone be more suitable for long distance- just because he has slimmer built and he Hasn't got enough speed to be an elite sprinter so he goes for long distance, or again some internal differences?