Abstract: A bicycle crank assembly comprises pedals, crank arms, an axle and a chainring assembly. The pedals, crank arms, and axle are coupled to the chainring assembly through an elastic element in the form of a U-shaped spring. This elastic coupling allows relative angular rotation between pedals and chainring proportional to the force exerted on the pedals by a bicycle rider. The proportionality constant, or elasticity, is adjustable by repositioning the spring within its supporting structure. The elasticity may be thus adjusted to enable accurate calibration of measurement instrumentation associated with the crank assembly, or for any purpose for which an adjustable elastic coupling is desirable.