For many bodybuilders and other strength athletes the weak spot in the shoulder joint is the external rotator cuff: small muscles to the rear of the shoulder joint which stabilise the joint during intensive exercises. If you want to strengthen these muscle groups and keep your shoulder joint free of injury, it’s worth taking a look at the interesting results of a study that sports scientists at the American Sports Medicine Institute published in 2004.
The researchers attached electrodes to the shoulder muscles of 10 subjects so they could measure how hard the muscles had to work. They then got the subjects to perform 7 exercises that strength athletes do to make their shoulder joint more stable.
The muscle groups that are most interesting are shown below: the teres minor, the infraspinatus and the supraspinatus. All three together make up the external rotator cuff.
The side-lying external rotation turned out to be the most effective exercise for the teres minor, as the figure below shows.
The side-lying external rotation exercise is shown in the photo below right.
On the left above you can see the prone horizontal abduction at 100 degrees with full external rotation. The name’s a bit of a mouthful, but in this case it’s justified. According to the figure below, it’s the most effective exercise for the supraspinatus.
Regular readers of this free webazine will already know that this exercise – aka prone full can – is a really good one for strengthening the supraspinatus. A study we wrote about a month ago came to the same conclusion.
For the infraspinatus, the side-lying external rotation turned out to be the most effective, as the figure below shows.
Electromyographic analysis of the rotator cuff and deltoid musculature during common shoulder external rotation exercises.
Prospective single-group repeated-measures design.
To quantify electromyographic (EMG) muscle activity of the infraspinatus, teres minor, supraspinatus, posterior deltoid, and middle deltoid during exercises commonly used to strengthen the shoulder external rotators.
Exercises to strengthen the external rotators are commonly prescribed in rehabilitation, but the amount of EMG activity of the infraspinatus, teres minor, supraspinatus, and deltoid during these exercises has not been thoroughly studied to determine which exercises would be most effective to achieve strength gains.
METHODS AND MEASURES:
EMG measured using intramuscular electrodes were analyzed in 10 healthy subjects during 7 shoulder exercises: prone horizontal abduction at 100 degrees of abduction and full external rotation (ER), prone ER at 90 degrees of abduction, standing ER at 90 degrees of abduction, standing ER in the scapular plane (45 degrees abduction, 30 degrees horizontal adduction), standing ER at 0 degrees of abduction, standing ER at 0 degrees of abduction with a towel roll, and sidelying ER at 0 degrees of abduction. The peak percentage of maximal voluntary isometric contraction (MVIC) for each muscle was compared among exercises using a 1-way repeated-measures analysis of variance (P< .05).
EMG activity varied significantly among the 7 exercises. Sidelying ER produced the greatest amount of EMG activity for the infraspinatus (62% MVIC) and teres minor (67% MVIC). The greatest amount of activity of the supraspinatus (82% MVIC), middle deltoid (87% MVIC), and posterior deltoid (88% MVIC) was observed during prone horizontal abduction at 100 degrees with full ER.
Results from this study provide initial information to develop rehabilitation programs. It also provides information helpful for the design and conduct of future studies.
PMID: 15296366 [PubMed - indexed for MEDLINE]