Following on from the shoulder evaluation:
If you really wanted to isolate the supraspinatus for testing or treatment, we can look at muscle activation studies. These aimed to find the best exercises to strengthen it.
Reinold et al (2004) found the greatest amount of activity of the SS was observed during prone horizontal abduction at 100 degrees with full ER (best for strengthening). His later study found that the full-can exercise may be best to maximize the amount of SS activity with the least amount of deltoid muscle activity (best for isolating) (Reinold 2007). This suggests prone horizontal abduction at 100 degrees with full ER may be the optimal position for specific rehabilitation (cue the functional rehabilitation debate), and the full-can exercise to recruit the SS muscle for testing. All pretty surprising when we thought the empty can isolated the supraspinatus!
Thinking about it a bit more, it makes sense that if you wanted to improve activation of a shoulder muscle (or any muscle), it would be best to move the arm in a plane in which the fibers are directed through. In Reinolds 2004 study (and Boettcher et al 2009) where the subject was prone, they found the greatest amount of activity (not isolation) in 100 degrees of abduction. This position would have lined the SS’ fiber direction with the humeral angle nicely.
This is also best done in external rotation and according to Huges et al 2013, the infraspinatus is best isolated in 90’ shoulder flexion (with neutral being a close alternative). An interesting find in this study was that regardless of shoulder position, the oblique head would always be working harder than the transverse head… clinical relevance? Well earlier in this series we spoke how this oblique head has the big responsibility of helping that inferior glide and migration of the humeral head in abduction… so a greater activity in these oblique heads is functionally desired.
Its fun to discuss which test is best/worst for whichever muscle, but with all this being said, it is important for us not forget what we want these tests to do… which is signal a problem by straining these tendinous insertions… to indicate a rotator cuff pathology.