The horsepower made a great deal of sense in its time. It was defined by James Watt as 550 foot-pounds of energy per second, and it enabled him to go to prospective customers for his steam engines and say "Now if you buy one of my engines, this is how many horses you can get rid of"...

We know now that the horse or any other biological "machine" really sucks as a standard, because its power output depends a great deal on how it's coupled to the load. When Bryan Allen pedaled the Gossamer Albatross across the English Channel in 1979, he had to AVERAGE 1.3 hp for four hours.

rj