The aim of this study was to use a surface electromyographic (sEMG) technique with a ballistic isotonic shoulder joint adduction movement to determine the function of the neuromuscular compartments (NMCs) within the Pectoralis Major, Deltoid and Latissimus Dorsi muscles. Sixteen male subjects (mean age 22 years), with no known history of shoulder pathologies, volunteered to participate in this study. The timing and intensity of muscle contraction, recorded with 15 pairs of bipolar sEMG electrodes, were compared during the performance of a 40' coronal-plane ballistic (movement time (MT) <400ms) shoulder joint adduction movements. The results of this investigation have suggested that heterogenous sEMG was present across the breadth of all three muscles indicating the presence of individual NMCs with significant (p<0.05) differences observed within the three muscles either in NMC onset (ON), duration (DUR), the timing of peak NMC intensity or the relative intensity of NMC activation. For example, within the Deltoid, NMC activation was closely related to MA (moment arm) length with the NMC with the largest antagonist moment arm (MA) Deltoid NMC3 (D3) having a late period of activation (Antagonist (Ant)) to slow glenohumeral joint (GHJ)rotation and maintain its final joint position (with Agonist 2 burst (Ag2)). The most obvious triphasic EMG patterns (e.g. Ag1-Ant-Ag2) were observed between the first NMCs activated in the two agonist muscles and the last NMC activated in the antagonist Deltoid muscle. In conclusion, our findings suggest the presence of in-parallel NMCs within the superficial muscles of the GHJ and show that biomechanical parameters, such as the MA at end-point movement position, influence the function of each NMC and its contribution to alternating patterns of agonist and antagonist muscle activity typical of ballistic movement. '