A computer program product comprising instructions which, when executed by at least one processor of an electronic control unit for a drive system of an electric bicycle, cause the at least one processor to carry out a method for controlling a drive system of the electric bicycle, in which a drive power can be applied by muscle power via a bottom bracket shaft for moving the electric bicycle forward, and an assistance power can be applied in addition to the drive power, by external power, via at least one drive motor operated in a travel mode, wherein a torque applied to the bottom bracket shaft by muscle power is calculated using an acceleration signal representative of the acceleration of the electric bicycle and a rotational speed signal representative of a rotational speed of the bottom bracket shaft, and the assistance power is controlled on the basis of the calculated torque.