Chris you ask a lot of broad questions when the answers are really multifaceted and complex. Are you asking which muscle is the most often injured out to the group of Supraspinatus, Infraspinatus, Teres Minor, and Subscapularis?
The weakest is totally dependent on the client’s history and activities. If I experienced a serious Teres Minor tear at some point and never had it evaluated or treated, that is most likely going to be the weakest of the group.
This is a good question. I recently became certified in NKT, Neurokinetic Therapy. This approach looks at facilitated muscles vs inhibited muscles and how to create balance between the two. I have my own view points here. I wanted to get feed back from my NKT colleagues and here is what we came up with.
The rotator cuff is more often ‘strong’ than ‘weak’. The muscles that tend to cause the rotator cuff muscles issues are often times inhibition in latissimus or deltoid. Usually the adducting fibers of the lat and medial deltoid. The supraspinatus often times time on an extra work load when these muscles are not firing correctly. and the other rotator cuff muscles is joint centration.
Posture, positioning, soft tissue quality all need to in good positioning for the rotators to fire correctly. The supraspinatus synergistically abducts the mid delt and usually overcompensates when timing and proprioception of other muscles are not firing correctly.
In shoulder issues, especially with abduction, check the relationship between the supraspinatus & middle deltoid. When a larger, global muscle such as the mid delt becomes inhibited, its synergist, the supraspinatus, a smaller, local muscle usually compensates.
For more information look into NKT or check out my website @ www.bodyarch.com.