2019-02-01_Popular_Science

22 SPRING 2019 • POPSCI.COM by Claire Maldarelli / illustrations by Moron Eel

THE HUMAN BODY EVOLVED EXPRESSLY TO MOVE. WE RUN, JUMP, AND CLIMB 

as soon as our tiny limbs allow it. But a select few thrill-seekers go much further, hungry to

push beyond our species’ more-mundane corporeal capabilities. The most extreme among

us fling, squeeze, and stretch their bodies in the name of guts, glory, and even entertain-

ment. Here’s what all that abuse does to their agile-but-fragile frames.

An elite endurance run-
ner can log hundreds
of miles on their feet.
While they pound the
pavement, their brain
diverts blood away
from the intestines to
give heart, lungs, and
muscles a boost. That
means the risk of
gastrointestinal
distress [1] increases.
Sleep deprivation—
especially combined
with lack of oxygen
and glucose—triggers
hallucinations [2] in
most racers. And all
the outdoor training
means greater expo-
sure to pollen, leading
to an above- average
incidence of allergies
and asthma [3].

Ultra running

Freediving

Many land-dwelling

species share a trick

called the diving

response: When we

stop inhaling and get

our nostrils wet (sure-

fire signs of aquatic

submersion), our

heart rates drop [1] by

up to 50 percent, and

peripheral blood ves-

sels constrict [2],

conserving oxygen for

tickers and brains. The

Bajau— an indigenous

population near Indo-

nesia who freedive for

fish—have spleens [3]

twice the typical size.

The organ regulates

red-blood-cell circula-

tion; a larger spleen

delivers more oxygen-

carrying cells.

Skydiving

Air pressure decreases

during the ascent but

shoots up during the

fall, a shift that can

cause vertigo and

ruptured eardrums [1].

A 10,000-foot drop

lasts a minute or less,

but fright can throw

off the brain’s [2]

stopwatch: Research

suggests that fearful

flyers will think they’ve

fallen for longer. All

divers see a spike in

hormones [3] such as

adrenaline, which

tenses muscles and

speeds up breathing

and heartbeat. The

rush is meant for

fight-or-flight, but

skydivers don’t have

much of a choice.

Racecar driving

Professional drivers
go beyond 200 mph,
and some races last
24 hours. Car interiors
can top 130 degrees,
which equals a lot of
sweat [1]; racers typi-
cally lose around 5
pounds during a three-
to four-hour event.
Stress and G-force
keep heart rates [2]
high— comparable to
a mara thon run—so
even though driving is
sedentary, pros stay in
shape with cardio
workouts. They also
strengthen their neck
muscles [3], which
support the equiva-
lent of an extra 60 to
90 pounds at peak
acceleration.

ANATOMY

ready, set, go!

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