It's common knowledge that sports, in general, make for increased metabolic rates and better overall fitness of the human body. Regular exercises, done daily, or at least 3 or 4 times per week, can help people's bodies become more efficient in the way they burn fats. This process, the human metabolism, is what extracts everything people need from the food they eat and converts it into energy.

Professional athletes have far better metabolic rates than regular people, simply because years and years of training have modified their bodies in a way that allows it to rapidly digest and convert a large quantity of nutrients, for the maximum output of energy, at any given time. A long-distance runner, for example, has the whole body perfectly adapted for this type of course.

His muscular fibers are used to rarer contractions, over long periods of time, and generate just about the same amount of energy at all time, for a sustained effort. On the other hand, short-distance runners, who rely on speed, have a body that is used to having everything drained out of it in a very short burst, as in a 100 meter (330 feet) sprint.

Yale University scientists, led by professor Douglas Befroy, say that responsible for the performances athletes are capable of is the very high number of muscular mitochondria, which are cell components very similar to energy converters – they burn fats and sugars inside the cell and create energy-carrying ATP molecules, which provide the muscles with increased oxygen-processing capabilities. Ultimately, the result of many mitochondria is the ability the muscles have, of working better for longer.

The researchers also discovered that professional athletes also burn more energy even when they're resting or sleeping, not only during busy periods. This means that the excess energy that is generated by mitochondria is transformed into heat and is lost.

Discoveries such as this one are very important for the field of medicine, because they can lead the way to better understanding how very dangerous diseases, such as diabetes, work and maybe even discover some potential cures.