A person has to exert pressure on the pedal in order to rotate the pedals and then to move the bicycle on the road. Usually, amount of work that the person must do is equal to the frictional force * distance traveled.
If he travels with a speed v then, the power he must exert on the pedals will be equal to Frictional force * speed. That is the minimum required.
If the tubes in the tires are not full with air and do not have sufficient pressure, then the force of friction is high. Also, the mechanical parts need good oiling to lubricate the motion. Perhaps ball bearings are worn out. If these are taken care of, then force required will be nearly equal to the minimum.