[KennyBlanken]

Leg muscles are the largest and most powerful in the human body and it's pretty easy for them to exhaust the body's aerobic capacity.

The number of muscles involved is not a limitation for longer duration power generation. There's aerobic capacity, but also glycogen and oxidative (fat) energy pathway efficiency. Experienced endurance athletes usually have quite high oxidative energy capacity/efficiency.

These sorts of projects are silly because even a decent average adult male will struggle to make 100-150W for an hour.

[mcronce]

You're absolutely right that projects like these are silly as anything more than a fun tinkering exercise, but that 100-150W number is a low estimate. I'm fairly small and out of shape and can produce 180W for an hour. In-shape amateurs can do better than that.

Still not enough to be even remotely practical as a generation method, but substantially more than 100-150W

[kitd]

Leg muscles are the most powerful in he body, but they are not used to the extent on a bike as they are on a rowing machine. Additionally, they extend the work done by the arms and back, ie the work is not just the sum of the individual muscle movements, but the combined action.

Yes, it is silly and the author intimates that in the OP and the article I linked too, but I don't think meaningful power generation is the point of the exercise.

BTW a decent average male should be able to do 100W easily for an hour. I'm a (not particularly powerful) rower in my 50s and can easily sustain 150W for an hour, ie circa 120W accounting for generator inefficiencies.