Well everyone it is that time of the week again, the time to nerd out and get our research review on! Today's study is especially helpful for those individuals who want better developed, more stable, and better looking shoulders. Hope you all find benefit from it. It is was a straight forward study with very conclusive results. Effect of hand position on EMG activity of the posterior shoulder during a horizontal abduction exercise by Schoenfeld, Sonmez, Kolber, Contreras, Harris, and Ozen published in the Journal of Strength and Conditioning Research.


The posterior deltoid has been credited as the prime mover in shoulder horizontal abduction as well as an external rotator of the shoulder complex. It's believed that the posterior deltoid is important for shoulder health and stability making it often a target area of strength and size development in most training programs. But it hasn't been established which exercise optimizes the development of this muscle though there are a few popular ones such as the band pull apart, reverse fly, and face pulls. Previous research has indicated that the effectiveness of an exercise to activate the posterior deltoid can be affected by how internally or externally rotated the shoulder is as abduction takes place. The researchers in this study wanted to investigate the effects of shoulder joint rotation on the activity of the posterior deltoid while performing the reverse fly exercises.


Researchers measured the activity of the posterior deltoid, external rotator, infraspinatus, and middle deltoid while performing the reverse fly with the shoulder in various degrees in rotation. 19 male subjects were recruited who had been performing resistance exercises for at least a year previous. Surface electrodes were placed on all the desired muscles to be measured.  Prior to measuring the activity in the reverse fly the researchers measured the maximal voluntary isometric contractions for the posterior deltoid with the shoulder flexed at 90 degrees and maximum abduction against manual resistance. 5 minutes following this measurements the subjects performed seated reverse fly with either a pronated or neutral hand position in a counter balanced order. Subjects performed as many repetitions as possible. 75% of body mass was used as the resistance.


Researchers found the EMG activity of the posterior deltoid was greater with a neutral grip than with a pronated grips. In addition they found that EMG activity of the infraspinatus was greater with a neutral grip. Researchers noted that there was a trend for EMG activity of middle deltoid to be greater with neutral grip, but not statistically greater.


Researchers concluded that the posterior shoulder was activated more when the reverse fly was performed with a neutral grip hand position. Researchers hypothesized this may have been do to the fact that the internally rotated position of the shoulder in a pronated grip prevents the posterior deltoid from acting as an external rotator. Or perhaps that the starting position in internal rotation alters muscle fibers length to tension relationship.

This study's implications for us people who want to develop bigger and stronger posterior musculature should be using a neutral to supinated hand position for greater activation of the posterior shoulder. The greater activation will result in more muscle fibers being recruited and fatigued leading to greater levels of hypertrophy.

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