Phasic relations in 90 degree abduction-adduction of the arm: the ARIMA representation

Myoelectric signals (MES's) from the medial deltoid, posterior deltoid and medial trapezius were analyzed during 90 degree abduction-adduction cycles of arm movement. Two healthy males were utilized as subjects. The MES's records were divided into sub-sections of 50 ms of duration, and each segment was described by a suitable model. The models were based on autoregressive integrated moving average (ARIMA) processes. Several distinct phases were discerned within a given movement cycle, each phase being associated with a distinct type of ARIMA process. Phasic relations among the three muscles were then revealed. A simple test was suggested to detect the onset of muscle activity in real-time situations.