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In our laboratory for biomechanics, a new isolation amplifier was developed with which to record the electromyographic activity of muscles inaccessible to surface electrodes, in particular that of the rotator cuff. Our basic premisses were maximum safety for the patient or subject investigated, and optimal signal processing. These were achieved by a triple galvanic separation of the patient/subject from the battery power supply and the signal cables and by careful selection of the electronic components.

We have carried out an electromyographical examination of the activity of five different regions of the deltoid muscle during abduction/adduction in various body postures with different biomechanical actions of arm gravity. The results show that the deltoid action is highly differentiated in its different regions and is not restricted only to the generation of an abducting moment in the shoulder joint. There is obviously a biomechanical contribution, mainly by its spinal and clavicular regions, to the stabilization of the glenohumeral joint and to the control of the selected plane of abduction.