US Patent 10286978 Bicycle crank arm with strain gauge

A bicycle crank arm includes a crank body, a metal pad, and a strain gauge. The crank body includes an outer layer which is made from a fiber reinforced resin material, and which extends in a longitudinal direction to surround a body axis. The metal pad is made of a ductile metal, and has a first surface and a second surface which is opposite to the first surface, and which has a predetermined surface area that is disposed on and strained with the outer layer. The strain gauge is disposed on the first surface of the metal pad and is configured to detect mechanical deformation of the metal pad corresponding to a pedaling force applied to the crank body.