Effects of Fatigue on Rotator Cuff and Scapulothoracic Muscle Performance
Authors: Hagan, K, May, A, Bringman, D, Davies, GJ
Institution: Biodynamics and Human Performance Center. Armstrong Atlantic State University. Savannah, GA.
Davies, GJ, Hagan, K, May, A, Bringman, D. Effects of Fatigue on Rotator Cuff and Scapulothoracic Muscle Performance. Research Platform Presentation. 4th International Congress of Shoulder and Elbow Therapists. Nogoya, Japan, April 11-13, 2013
Purpose: Research demonstrates fatigue of the rotator cuff (RTC) muscles causes altered glenohumeral kinematics, leading to shoulder pathologies. The purpose of this study was to evaluate the effects of fatigue on bilateral: RTC and scapulothoracic (ST) muscles using handheld dynamometry (HHD), proprioception, and isokinetic testing for total work (TW). We hypothesized fatigue of the dominant (D) RTC muscles would lead to bilateral weakness of RTC, ST muscles, and decreased proprioception.
Subjects: 31 college subjects (8 men and 23 women with a mean age of 21.87) without shoulder pathologies.
Methods: Tester and outcome measures were randomized along with examiners being blinded to test results. Subjects performed strength testing of 7 ST muscles in randomized order for D or non-dominant (ND) arm using HHD, proprioception testing, and isokinetic muscle performance testing for TW followed by the contralateral arm in same order for pre-fatigue testing. Subjects lay prone on a plinth with 5% of their body weight in the dominant hand and performed the fatiguing intervention. They moved the arm in horizontal abduction and external rotation at 90 degrees with the elbow at 0 degrees. A string at a 45 degree angle was premeasured and taped to the end of the plinth and used as the target ROM for the movement. The subjects completed as many repetitions as possible until they could no longer perform the motion to a 45 degree angle 3 consecutive times, which demonstrated at least a 40% reduction in abduction strength. Post testing was performed using D arm followed by ND arm starting with HHD, proprioception testing, and then isokinetic testing due to rapid muscle recovery.
Results: Paired T-tests demonstrated that the ER of ND arm had significant decreases in TW at all isokinetic speeds after the fatigue protocol (p <0.01). The D arm also had decreases in TW at 60?/sec (p <0.02) and 120?/sec (<0.01).For HHD, a significant difference was seen in D ST muscles (p<0.01-0.04) and ER with values ranging from (p<0.01-0.02). Proprioception and ND ST showed no significant effects.
Conclusion: Fatigue of D arm RTC lead to impaired bilateral ER isokinetic testing of TW. HHD also demonstrated weaknesses of the D ER RTC and ST muscles. Fatigue leads to weak ER and ST which may contribute to shoulder pathologies.