new swimming

techniques, the

democratization of sport, the

to new bodies and to new

populations around the world, and imagination in sport, an

of what the human

body is truly

of, have conspired to make athletes stronger,

faster,

.

acts as a limiter, preventing us from accessing

all of our

or

. But the more we learn about how that limiter functions, the

more we learn how we can push it back just a bit, in some cases by

convincing the

that the body won't be in mortal danger by pushing harder.

Endurance and ultra-endurance sports serve as a great example.

Ultra-endurance was once

thought to be harmful to human health, but now we realize that we have

all these

that are perfect for ultra-endurance: no body fur and a

glut of

and long

legs compared to our

for shock

absorption. We

have an

that are

better for pushing

than for grasping tree limbs, and when we run, we

can turn our

straight. Our

primate cousins can't do that. They have to run like this. And we have

big old butt

muscles that keep us upright while running. Have you ever looked at an

ape's butt? They have no

, whatever sport. And this showed in athletes' bodies.

In the 1920s, elite high-jumpers and elite shot-putters

were the same

into certain athletic

niches were a better idea. A form of

artificial selection took place, and athletes' bodies became more different

one

another.

elite shot-putter is

pounds

swim. The

record is always trending

.

Rather than stopping and turning around, athletes could somersault

under the water and get going right away in the

direction.

This second

cliff, the introduction of gutters on the side of the pool that

water to splash

, rather than becoming turbulence that impedes the

swimmers as

they race. This final cliff, the introduction of full-body and

low-