**2. History of BSA formulas**

In the late 19th century, Max Rubner introduced the 'surface' hypothesis that the metabolic rate of any animal is closely related to BSA. (Rubner, 1883) Although we know today that this assertion is not correct, the surface hypothesis was well embraced at that time and considered as a law. Since measuring heat production with direct calorimety is rather complex, BSA was seen as an alternative for reflecting the metabolic rate. The question then became how to measure BSA?
