Harness-seat beefy leg bike

I am reading the Amber books. The protagonist is really strong. He rides a horse, as fantasy heroes do. I was thinking he might be better served by a mountain bike.

But can one apply fearsome strength on a bike? Real life bike people have big legs, but it seems to me they still stand up when pedaling. I am aware that there exist puny toe clips which allow for a modicum of upward pull. But downward force would seem to me limited to a force equal to the gravitational pull on the bikers body. If the biker pushes harder that that (as is obviously possible) part of the force is wasted in lifting his body above the seat.

The beefy leg bike really is just a bike in which the biker is harnessed onto the seat. Now downward push of the pedal pushes the pedal instead of lifting the biker's body. Those beefy legs can really get into the action.

BUNGCO recommends that superhumans and cyborgs interested in this line of bikes notify us in advance. For a nominal upcharge and advertising rights we will upgrade the load bearing capacity of other components on your bike. Truly powerful legs may cause failure of components which under normal circumstances do not experience such forces. For example the seat might tear loose from the frame while remaining attached to your backside by the harness, which is undignified and difficult to repair at speed.