Why can't a couch potato run a marathon?

Intuitively, it makes sense that a trained athlete can run a marathon easily, while a "couch potato" can barely run a mile. But what's the biology behind it? Find out how fit and unfit bodies respond to exercise in this episode.

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Episode Transcript

Speaker 1 (00:00):
Welcome to brain Stuff from house stuff marks dot com
where smart happens. Hi, I'm muscle brain with today's question
why can a trained athlete run a marathon but a
couch potato can't run half a mile? If you're out

(00:21):
of shape, you know it. Even climbing a flight of
stairs can leave you out of breath if you haven't
been exercising regularly. Even a little exercise like going up
the steps can put a strain on your body. Your
body responds to exercise with a coordinated effort that involves
many systems, including your muscles, your heart, your lungs, your

(00:43):
blood vessels, your skin, your brain, and several others. When
you do exercise, all those systems are working together. For example,
the muscles provide the strength, power and endurance to do
the exercise. Enzymes within those muscles mobile wise various fuels
to provide a t P to meet the energy demands

(01:04):
of the working muscle. The heart and blood vessels increase
the blood flow to deliver more oxygen to the working muscle.
The lungs increase the rate of breathing to deliver more
oxygen to the muscle. All of these systems can be
improved by training. Lack of training causes them to atrophy.
Let's compare the couch potato with the trained athlete. The

(01:27):
couch potato has several different problems. First, there are weakened
or atropheed muscles. Second, there's weakened or atropheed heart muscles. Third,
there's decreased metabolic enzymes in the muscles. Fourth, there's diminished
lung capacity, and fifth there are the wrong metabolic fuels.

(01:48):
If muscles aren't used regularly, their mass decreases, and so
does their ability to store energy. The muscle proteins and
fibers that develop the force diminished. Therefore, the couch potato
simply can't generate the force required for the physical activity
involved in running a marathon. The heart is a muscle,
just like skeletal muscle. It also adapts to a less

(02:11):
active state by losing muscle mass. While this doesn't affect
the couch potatoes ability to pump blood to his or
her tissues, it limits the ability to increase the blood
flow during exercise. The heart will not be able to
stretch as far or develop the pressure required to increase
the cardiac output. That's why doctors tell you that you

(02:33):
need to exercise regularly to keep your heart in shape.
The enzymes involved in anaerobic which means without oxygen, and aerobic,
which means with oxygen metabolism help provide the energy to
working muscle. In the couch potato, however, the level of
these enzymes goes down, so the inactive person's body can't

(02:55):
metabolize fuel as well as an athlete's body can. The
fuels used in the body during exercise mainly come from carbohydrates, glucose,
muscle glycogen, and some fat. However, the couch potato has
mostly fat and probably little glycogen available in the muscles.
It takes longer to metabolize fat as a fuel than

(03:17):
it takes to metabolize glycogen. That means that the breakdown
of fat can't keep pace with the energy demands of
working muscle. All of these different factors combined to limit
the ability of the couch potato to exercise. The good
news is that with a moderate exercise program, the couch
potato or anyone else, can improve their fitness and their

(03:40):
bodies response to exercise at least enough to do a
ten k run. Be sure to check out our new
video podcast Stuff from the future. Join House to Work
staff as we explore the most promising and perplexing possibilities
of tomorrow. The House to Works I Find app has
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