A circuit for tuning a transconductance amplifier includes a first transconductance amplifier outputting a first current from its output, a second transconductance amplifier outputting a second current from an output that is coupled to the output of the first transconductance amplifier, and a feedback loop. The flow aid and the head part, which may be designed with a screw thread, are connected to form an insert, which by insertion in the housing can be connected thereto, a flap comprising a grounding lug being connectable to the head part. A contact sensor is provided at the end of the footrest, wherein when the contact sensor detects contact with an obstacle, downward rotation of the leg rest is stopped and the footrest is moved backward. In one aspect of the invention, a content bearing medium is provided.