If its got a gasoline motor, and you want to use the public highways , and streets .
You have a Motor Vehicle, you will be cited if the constabulary sees you ..

[ if you keep it on the farm and off the roads you don't. then its like a farm tractor.. ].

for clarification contact the DMV in the state where you live.

Pedal Electric Bicycles Fall in a different category,
because when you stop pedaling the motor assist quits.

standing ,there are weird exercise things, like the Horse on a treadmill Bus..

thing about a Bicycle is by not standing, but seated,
the muscles can turn the pedals more easily, than walking, and supporting your weight.