The force and energy used are related. The force, measured in pounds or Newton's, is how hard you push on the pedals. The energy is that number multiplied by the distance the pedal moves. For example if you press on the pedal with an average force of 20 pounds and the pedal moves in a circle 3 feet in circumference, you expend 60 foot pounds of energy with each complete revolution of the pedal.
A more customary measure of the effort involved is power. Power is the rate at which energy is expended. If you were pedaling at a rate of two revolutions of the pedal per second, using the numbers from the example above, you would be expending 120 foot pounds of energy per second. One ordinary unit of power is the horsepower, which is 550 foot pounds per second. The rider in our example would be producing 120/550 horsepower or about 0.22 horsepower.
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