Influence of different ranges of motion on selective recruitment of shoulder muscles in the sitting military press: an electromyographic study

Popular fitness literature suggests that varying the elbow range of motion (ROM) during the Military press can lead up to specific muscle isolation especially for deltoid and trapezius muscles. The purpose of the study was to examine the effect of ROM at different loads on the electromyographic (EMG) activity of 8 preselected muscles. Six experienced lifters performed 3 sets of 10 repetitions, each one with a different ROM: the first one with a final elbow angle of 90[degrees] (R1); the second with 135[degrees] (R2), and the last one with a final elbow angle of 180[degrees] (R3). Three resistances were chosen (no load, 30% of one repetition maximum [1-RM], and 70% of 1-RM), and sets were separated by 5 minutes rest. Electromyographic surface electrodes were placed on the clavicular head of pectoralis major, anterior deltoid, medial deltoid (MD), posterior deltoid (PD), upper trapezius, middle trapezius (MT), long head of triceps, and teres minor (TM). Analysis of variance showed a significant increase of rmsEMG activation with the widest ROM for each muscle and for each load condition except in MT and TM and PD with no load. The results showed that the use of the widest ROM increased the EMG activity of all the muscles selected with respect to the closest one, whereas this effect is not totally confirmed with the employment of R2. In addition, the use of intermediate ROMs was able to isolate the activity of the MD with respect to the trapezius only in the condition of the heaviest load. This suggests to coaches that in strength development programs the employment of an incomplete ROM can reduce the involvement of the trapezius without decreasing medium deltoid activation only with heavy loads. KEY WORDS muscle activity, muscle isolation, resistance training