A feedback loop system for monitoring rehabilitation of a muscle, the system comprising: a user interface (14, 14')configured to receive a first input from a user defining a stimulation protocol comprising a plurality of parameters for generation of an electric current; a transcranial magnetic stimulation device communicatively coupled to the user interface (14, 14') to receive the stimulation protocol, the transcranial magnetic stimulation device comprising an inductive coil positionable over a patient's skull and configured to generate an electromagnetic field in accordance with the stimulation protocol to cause contraction of the skeletal target muscle associated with control of the lumbar spine; an implantable device configured to be implanted in or adjacent to tissue associated with control of the lumbar spine, the implantable device comprising a recording electrode (12, 12') and a processor (13, 13') configured to receive, detect, and record a response signal generated by the body in response to the electromagnetic field; characterised in that the system further comprises: a trigger detector (16, 16') communicatively coupled to the transcranial magnetic stimulation device and configured to transmit a wireless signal to the implantable device upon application of the stimulation protocol, the wireless signal configured to initiate signal processing of the response signal by the implantable device; an external receiver comprising an electromagnetic or radiofrequency telemetry unit wirelessly coupled to the implantable device and configured to receive the response signal from the implantable device; and an output display (17, 17') having a screen configured to display data representative of the response signal. a user interface (14, 14')configured to receive a first input from a user defining a stimulation protocol comprising a plurality of parameters for generation of an electric current; a transcranial magnetic stimulation device communicatively coupled to the user interface (14, 14') to receive the stimulation protocol, the transcranial magnetic stimulation device comprising an inductive coil positionable over a patient's skull and configured to generate an electromagnetic field in accordance with the stimulation protocol to cause contraction of the skeletal target muscle associated with control of the lumbar spine; an implantable device configured to be implanted in or adjacent to tissue associated with control of the lumbar spine, the implantable device comprising a recording electrode (12, 12') and a processor (13, 13') configured to receive, detect, and record a response signal generated by the body in response to the electromagnetic field; characterised in that the system further comprises: a trigger detector (16, 16') communicatively coupled to the transcranial magnetic stimulation device and configured to transmit a wireless signal to the implantable device upon application of the stimulation protocol, the wireless signal configured to initiate signal processing of the response signal by the implantable device; an external receiver comprising an electromagnetic or radiofrequency telemetry unit wirelessly coupled to the implantable device and configured to receive the response signal from the implantable device; and an output display (17, 17') having a screen configured to display data representative of the response signal. a trigger detector (16, 16') communicatively coupled to the transcranial magnetic stimulation device and configured to transmit a wireless signal to the implantable device upon application of the stimulation protocol, the wireless signal configured to initiate signal processing of the response signal by the implantable device; an external receiver comprising an electromagnetic or radiofrequency telemetry unit wirelessly coupled to the implantable device and configured to receive the response signal from the implantable device; and an output display (17, 17') having a screen configured to display data representative of the response signal.