A torque and power measuring device corresponding to the non-drive side cyclist leg, comprising a hollow shaft connecting the two bicycle crank arms with strain sensors arranged in the shaft surface. These sensors are connected to an electronic control unit housed inside the shaft, to which are also connected other different sensors to measure a plurality of interesting quantities (pedaling cadence, crank arm angular position . . . ). This electronic control unit picks the sensor signals up, stores them and performs pre-programmed software operations to later wirelessly output the result signals towards a receiving device for analysis and/or storage them, by means of an antenna located outside the shaft and anchored to the outer surface of the jointed crank arm with the shaft.