The present invention relates to a training apparatus comprising a training element (1) for a user performing exercises, an AC motor (3) and a frequency converter (5) being arranged to control the AC motor (3), wherein the frequency converter (5) comprises measuring means being arranged to measure a voltage and a current of the AC motor (3) and calculation means being arranged to calculate a magnetic state of the AC motor (3) using the measured voltage, the measured current, a reference torque and a reference flux in order to generate a torque of the AC motor (3). The training apparatus further comprises a control unit (6) having a machine control module (27) being arranged to calculate the reference flux and the reference torque using an intended overall torque, wherein the machine control module (27) is connected to the frequency converter (5) and arranged to transmit the reference flux and the reference torque to the frequency converter (5). Further, the present invention comprises a training arrangement comprising the training apparatus and a method for operating the training arrangement, This training apparatus is readily applicable to a training exercise for muscle of an exercising person.