In this thesis the design of a frictionless resistance system with a speed independent mechanical resistance is presented, this system is meant for the portable fitness device "DISQ". The goal of this device is to provide a mobile exercise similar to an exercise with weights but with more flexibility. The goal of the change from the current friction braking version to the one discussed in this thesis is to minimise wear on the device and to ease the user’s interaction with the device. This is accomplished by implementing the frictionless resistance with a rheostatic braking system which is controlled to provide the speed independent mechanical resistance. The control circuitry is fed by a battery system which is recharged through combining the rheostatic braking system with a small regenerative braking system. The system described in this document shows that the afriction less resistance for a portable fitness device can be obtained through rheostatic braking and that it’s also feasible to harvest energy from this process for powering the control system. The implementation discussed in this document is not yet sufficiently small and cheap for a commercially viable fitness device. It does however show that this method of implementing it can work and with further development a version can be made that is sufficiently small and cheap.