In engineering, specific power, also known as power per unit mass or power density, refers to the amount of power delivered by an energy source, divided by some measure of the source's size or mass. It is used to compare various power sources by a common figure representing their suitability for a particular role, such as watts/kg for a cyclist. This determines the acceleration the rider will experience for a given power, since weight is relativatly constant during the duraton of the race.
When the denomenator is close to 0, as in Janez's case, the accelerations can be impressive.
"I love fools’ experiments. I am always making them." - Darwin