Abstract: A rotor for rotating an electric machine having permanent magnets and flux concentration, including a shaft extending along the rotational axis of the rotor, a rotor body placed on the shaft, the rotor body having a central opening for the mounting thereof on the shaft; radially oriented recesses wherein the permanent magnets are placed; and in at least one angular space separating two consecutive recesses, at least one cavity leading neither to the central opening nor to the two consecutive recesses, the cavity or cavities located in the space occupying an angular area around the rotational axis of the rotor greater than or equal to half of the angular area of the space.