Dusty, I’ve looked into that. James Watt intended horsepower to be the amount of work a horse could do continuously, not as a matter or brief or peak power. A horse can produce about 15 horsepower for brief periods.
Humans are good for about 1.2 horsepower peak and 0.1 horsepower indefinitely.
Watt was too modest to call those units Watts, but he’d dead now and so we now say 1 horsepower is 745 watts.
Of course, what most people really want to know is how horsepower relates to the power output of ducks. It turns out that you need about 42 ducks to create 1 horsepower. Here’s a very helpful horse-to-duck horsepower calculator (German).
https://feinmechanik-rosenheim.de/horsepower-to-duckpower-calculator/
