The exoskeleton is characterized by four degrees of freedom (DOFs): three of them, e.g. shoulder elevation, shoulder rotation in the transversal plane and elbow flex-extension, are equipped with angle sensors (Vert-X 13 E, ConTelec AG) to measure the position and electromagnetic brakes to avoid the fatiguing and unnecessary use of FES to hold a target position once reached. The additional DOF is provided by an inclination module, which enables the patient to move the trunk 20° forward without constriction. In addition to the 4 DOFs, the humeral rotation, the prono-supination as well as the length of the forearm and the upper arm can be adjusted at the beginning of the training session at subject-specific positions. The gravity compensation modules for upper arm and forearm consist of a carbon fiber-tube with springs inside whose pre-tension can be adjusted at the beginning of the training session in order to change the level of compensation. Thanks to the adjustability of the lengths and the level of compensation, the exoskeleton can fit and support patients within 5th and 95th female/male percentile. The exoskeleton can be mounted on the user's wheelchair or on a normal chair by means of a universal clamping mechanism which assures easy and stable mounting. The exoskeleton weights about 4kg plus 2kg for the clamping mechanism.