While the U.S. brings home more Olympic gold than any other country, many, if not most, American school kids wouldn’t even bring home a tin, if there were such a low-ranking medal.

Recently, colleagues and I set out to see how the fitness of American kids stacked up relative to other countries. Our findings were surprising. Not only did the U.S. finish at the back of the pack, but U.S. kids ranked behind much smaller and some poorer countries, such as Iceland, Chile and Suriname.

Fitness level is an important indicator of sporting success, but it’s also important for your health. You can be fit in different ways – you can be strong like a weightlifter, run fast like a sprinter, be flexible like a gymnast or be skillful like a tennis player.

However, not all of these types of fitness relate well to your health. The most important type of fitness for good health is “aerobic” fitness, which is your ability to exercise vigorously for a long time, like running laps around an oval or biking around the neighborhood.

If you are generally unfit now, you are more likely to develop or die from conditions like heart disease, diabetes and some cancers later in life.

One study, using data from Aerobics Center Longitudinal Study which followed over 53,000 men and women, showed that low aerobic fitness was the strongest predictor of death. It was far greater than any other risk factor – with the exception of hypertension in men – and was greater than the combined deaths due to obesity, smoking and diabetes.

Recent evidence also shows that your fitness level as a child is strongly linked to your future health. Two studies, one that followed 1.3 million 18-year-old Swedish boys for 29 years, and another that followed 510 16-year-old Japanese girls for 64 years, found that children with low fitness levels were more likely to die prematurely from any cause later in life.

This highlights the importance of measuring aerobic fitness when trying to understand the health and well-being of children and youth.