I found a couple of interesting studies done on the effect of fatigue on shoulder proprioception. The rotator cuff has essentially two functions: to stabilize and depress the head of the humerus in the glenoid fossa. The following studies show how fatigue can create dysfunction in the shoulder.
In the second study the authors demonstrated that fatigue in the rotator cuff caused superior head migration. In other words the ability of the rotator cuff to depress the humerus was compromised. Allowing the humerus to move upwards decreases the sub-acromial space which isn’t a good thing. This space was decreased by up to 40% which is hugely significant.
The most interesting thing in this study is the authors had subjects perform one set of prone T’s with the thumbs up to failure. Failure was noted after the subject couldn’t raise the weight past 45 deg. and at least 40% decrease in strength was noted. Overall, the average degree of fatigue was indicated by a 54% reduction in prone horizontal abduction. The average weight used for the protocol was 3.94 kg and the average time to fatigue was 84 seconds.
The second study should open eyes as after one set of 90 seconds, the cuff can be fatigued enough to create sub-acromial impingement. Now think of all the athletes with shoulder problems that get blasted with 40 sets of RTC exercises everyday in an effort to strengthen their shoulder.
The problems are not only in a single workout but can carry over to outside of the weight room. If the cuff is constantly fatigued stability fades and we don’t want to lose its strength and stability when a pitcher is throwing 94 mph off the mound in the 7th inning.
The problems with training the cuff to failure is that you create instability, which is something we’re trying to eliminate. Allowing the head of the humerus to move in a joint that is already having dysfunction may eliminate all the positives that are created with actually training the RTC.