Definition: "An ergogenic aid is any substance or phenomenon that enhances performance "

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Cardio works better the thinner you are

If you're overweight and combating this with more exercise, then a 2006 study published by physiologists at Washington University in AJP – Endocrinology and Metabolism contains interesting news. Whether the news is good or bad depends on your character. If you're an optimist by nature, then the article's good news. If you're a pessimist, well then it's not.

The researchers did an experiment with 15 men, all of whom were untrained and equally fit. Five of them were thin, with a body composition of 16 percent fat. Five of them were overweight, with a body composition of 26 percent fat. Another five were obese, with 30 percent fat.

The researchers got the subjects to cycle for 90 minutes at 50 percent of their VO2max. That's a level of exertion that you can keep up for a long time. While the men cycled, the researchers measured the amount of fatty acids that accumulated in their blood. To keep things simple, they just measured palmitate. They noticed that physical exercise led to a rise in the palmitate concentration. But the extent to which this happened was higher the less body fat the subjects had.

Cardio works better the thinner you are

By introducing labelled palmitate into the subjects' bodies, the researchers could see how quickly the palmitate left the blood vessels on its way to being burned by the muscles. Once again, there were differences between the groups. The thinner the subjects, the more fatty acids their muscles extracted from the bloodstream. The muscles of the thin men absorbed twice as much fatty acid than the muscles of the obese men.

Cardio works better the thinner you are

The thin men burned 24 percent more fatty acids than the overweight men did, and 11 percent more than the obese men. These differences were not statistically significant. The researchers did not look at the EPOC.

There was, however, a significant difference in the kind of fat that the subjects burned. The thin men burned relatively more fat from their fat reserves [plasma fatty acids]; the overweight and obese men burned more fat already stored in the muscles [non-plasma fatty acids]. That's to be expected. Fat people have more fat in their muscle tissue. The figure below gives measurements from the last half hour that the men cycled.

Cardio works better the thinner you are

Part of the reason for the differences can be put down to hormones. The fatter the men, the more insulin there was in their blood and the less adrenalin.

There’s a double message for fat people who want to reduce their fat reserves by exercising more. On the one hand, the slimming effect of exercise has less effect on their fat reserves than in thin people. But on the other hand, with every kilogram of fat they lose, they can expect their fat reserves to react better to exercise.

J Physiol Endocrinol Metab. 2004 Mar;286(3):E354-62.

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