Abstract: An apparatus that preferably takes the form of a collar for exercising or assessing the upper cervical flexor muscles to assist with headaches. The apparatus includes a resiliently compressible cushion that fits under the mandible of the user but not extending as far as the chin. The user bends their head against the cushion to achieve an elevated pressure and preferably maintains the pressure for a period of time. The absence of sensory feedback of pressure against the chin inhibits the drive to use muscles ofther than the upper cervical flexor muscles. The cushion may be an inflatable bladder so that the pressure against which the head works can be varied. The cushion preferably includes pressure measuring means to measure changes in pressure within the cushion to monitor the performance of the upper cervical flexor muscles.

Abstract: An AC resonant charger for a capacitive load, such as a PFN, is provided with a variable repetition rate unrelated to the frequency of a multi-phase AC power source by using a control unit to select and couple the phase of the power source to the resonant charger in order to charge the capacitive load with a phase that is the next to begin a half cycle. For optimum range in repetition rate and increased charging voltage, the resonant charger includes a step-up transformer and full-wave rectifier. The next phase selected may then be of either polarity, but is always selected to be of a polarity opposite the polarity of the last phase selected so that the transformer core does not saturate. Thyristors are used to select and couple the correct phase just after its zero crossover in response to a sharp pulse generated by a zero-crossover detector. The thyristor that is turned on then automatically turns off after a full half cycle of its associated phase input.