Is there a way to compare a human being to an engine?

Human muscles are essentially biological engines. In terms of efficiency, biological engines are amazing. Listen in as Marshall Brain calculates human efficiency in this episode.

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Episode Transcript

Speaker 1 (00:00):
Welcome to Brainstuff from house stuff Works dot com where
smart happens. I am Marshall Brain with today's question, is
there a way to compare a human being to an
engine in terms of efficiency? It turns out that biological engines,

(00:22):
which is what the muscles in your body are, are
pretty amazing in terms of efficiency. To find out how efficient,
let's look at how many calories a person burns while
riding a bicycle. If you look on the web, you'll
find that a person riding a bicycle at fifteen miles
per hour or twenty four kilometers per hour burns about
point o four nine calories per pound per minute. So

(00:45):
a hundred and seventy five pound person burns five fifteen
calories in an hour, or about thirty four calories per mile.
That works out to twenty one calories per kilometer. A
gallon of gasoline about four eaters, contains about thirty one
thousand calories. If a person could drink gasoline, then a

(01:07):
person could ride about nine hundred and twelve miles on
a gallon of gas, or about three hundred sixty per leader.
Considering that a normal car gets about thirty miles to
a gallon that's pretty impressive. A human being on a
bicycle is about thirty times more efficient than a car
going down the road. To be fair, to keep in

(01:28):
mind that a car generally weighs a ton or more,
while a bicycle weighs only thirty pounds. Cars also travel
a lot faster than fifteen miles per hour, but it's
still an interest in comparison. Note also that people can't
drink gasoline. However, people can drink vegetable oil, which contains
nearly the same number of calories per gallon. The people

(01:49):
riding in a race like the Tour de France are
riding more like twenty five miles per hour. Because air
resistance rises very quickly with speed, they're burning about three
times more calories, something like a hundred calories per mile
in a hundred miles stage of the tour. A racer
might burn something like eight thousand to ten thousand calories

(02:10):
in one day, so they're getting only about three hundred
miles per gallon. The only way to replace those calories
is to eat a lot of food. For more on
this and thousands of other topics, is that how stuff
works dot com, and don't forget to check out the
brain Stuff blog on the house stuff works dot Com
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(02:31):
or Twitter at brain stuff hs W