Never mind elite marathon runners, cardio exercise will NOT make you too thin.

The question has come up by fitness enthusiasts if a lot of cardio exercise can make a person too thin. I’m a personal trainer, and what makes a person too thin is that of taking in fewer calories per day than what one can burn.

Doing a ton of cardio, such as running 10 miles every day, will burn a lot of calories. A person who does this needs to eat enough to subsidize this kind of training.

If they appear gaunt and too thin, the cardio isn’t to blame; it’s that of not eating enough.

However, if a person who does a lot of cardio appears to be too thin, this doesn’t always mean he or she isn’t eating “enough.”

Winners of the Boston and New York Marathon always look “too thin,” especially the men.

In order to be this skilled at such a strenuous event, these athletes need to be well-fed.

Pounding out 26 miles is extremely grueling on the body; an underfed body won’t last long in a marathon.

In fact, people have been known to drop out early in marathons simply due to dehydration.

A serious long-distance runner consumes quite a bit of food in order to sustain many hours of training week after week. Long-distance events require well-trained slow-twitch muscle fiber.

People who excel in long-distance running are born with a high amount of slow twitch fiber relative to fast twitch fiber.

Slow twitch fiber is designed for endurance, while fast twitch is designed for short bursts of power, strength or speed.

Because slow twitch fiber does not grow in size, the most prolific marathoner will still appear too thin; their muscle mass is small; the slow twitch fiber is highly efficient at duration, not speed or power.

Speed and power athletes do not appear “thin” because their sports require well-trained fast twitch fiber, which does grow in size.

So here’s something that will shock you: The body percentage of an elite sprinter is actually lower than that of an elite marathon runner!

The sprinter, however, is not “thin” because he or she has significantly more muscle development (fast twitch fiber).

As long as one eats appropriately, a lot of cardio will not make him or her too thin.

Lorra Garrick is a former personal trainer certified through the American Council on Exercise. At Bally Total Fitness she trained women and men of all ages for fat loss, muscle building, fitness and improved health. 



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