If you're standing up.. (on one leg), then you're putting the full 292 pounds of weight into downward force at the cranks (mid crank revolution). Some people can pull up a bit. I don't know how much, but say you pull up with 10 pounds while standing, then you add essentially double that (upward plus downward force), to get over 310 lbs force into the cranks.

I suppose since the cranks are essentially falling away from you, you're not quite getting that full force, but it is pretty close depending on the cadence.

And, your legs support your body so they're used to lifting that 292 lbs (plus some if you lift weights), although full 1 legged squats can be difficult, but certainly not impossible.

Anyway, the forces you can put into the cranks might make a 100 pound rider cringe. Some of it will be taken up by it requiring more power to make the bike move, but some might also be appropriate to do more power at at slower cadence.