How is mechanical energy produced in a moving bike?

Kinetic energy is exerted from the human's legs especially the thighs, through their feet onto the pedals. This moves the chain which acts on the axle to turn the back wheel. Continual pumping of kinetic energy through the striated leg muscles and through the the knee joint keeps the axle moving. When not receiving kinetic energy, such as during coasting, the axle continues to turn the wheel through its rotations. Theoretically, on a flat surface or uphill, all the kinetic energy would be "used up" if no more is applied. But on a downhill, gravity and slope accelerates the kinetic energy previously given, even if no more physical energy is applied. Here, brakes act against the wheels turning, so the bike slows then can be stopped.