Measuring the kinematics of human body movements is important for several biomedical and non-biomedical uses, such as rehabilitation, sports medicine, control of virtual reality systems, etc. This is typically performed employing accelerometers, electrogoniometers, electromagnetic sensors or cameras, which however are usually bulky, or can cause discomfort to the user, or are insufficiently accurate, or require expensive instrumentation. As an alternative to those state-of-the-art systems, stretchable piezocapacitive sensors based on dielectric elastomers (DE) represent a recently described competitive technology, which might enable wearable, lightweight and cost-effective devices. DE sensors consist of stretchable capacitors whose mechanical deformation causes a change of capacitance, which can be measured and related to linear or angular motions, depending on the sensors' arrangement. Here, we present a wearable wireless system able to monitor the flexion and torsion of the lumbar region of the back. The system consists of two DE sensors arranged on shoulder straps, and a custom-made wireless electronics designed to measure the capacitance of the sensors and calibrate them when the user wears them for the first time. We describe preliminary results related to the characterisation of the sensors and the electronics.