A power measurement apparatus for an exercise machine may include an optical sensing component and a pair of code wheels supported by the frame of the exercise machine. The pair of code wheels may include a first code wheel having a plurality of first windows and a second code wheel having a plurality of second windows that individually at least partially overlap respective ones of the first windows to define respective effective window, the width of which may vary responsive to the application of power via at least one moment-producing assembly. The optical sensing component is operatively associated with the pair of code wheels to detect variations in the width of the effective window and thus measure the power applied via the moment-producing assembly.