ArticleEffects of muscle fatigue on 3-dimensional scapular kinematics1
Section snippets
Study design and participants
A 1-group pretest-posttest measurement design was used, with 1 investigator performing the entire testing procedure. Thirty subjects who indicated that they had no history of cervical or shoulder pain or pathology and who showed no range of motion restriction were recruited for this study. Based on previous kinematic data,29 the power to detect a difference of greater than 2° is better than 85%. There were 16 women and 14 men, with a mean age of 28±6 years, a mean height of 170±9cm, and a mean
Results
The ICC3,1 values for measurements of scapular motions were analyzed at the minimal, 30°, 60°, 90°, 120°, and maximal humeral elevations. All the ICC values were above 0.9, and the SE of measurement for each point ranged from 1.0° to 2.6°.
There was a significant effect of fatigue on the scapular resting position for all rotations. For posterior tilting, significant changes were found up to 90° of humeral elevation. The biggest mean difference was approximately 4° at the beginning of arm
Discussion
The results of this study indicate that scapular kinematics can be temporarily altered with fatigue of the external rotators. All 3 rotations were altered after the fatiguing exercise; however, the maximal increase was no more than 4°. However, for posterior tilting, this represented almost a 50% change in rotation after the fatiguing exercise. This is consistent with other studies showing small changes in scapular kinematics with fatigue,12, 13 resistance level,37, 38 passive positioning,37, 39
Conclusion
This study showed that small but potentially clinically significant changes in scapular kinematics were found after an external rotation fatigue protocol. The altered scapular 3-dimensional movements occurred in the first part of arm elevation in the scapular plane. The fair to good correlation (r range, .39–.60) between the changes in scapular posterior tilting and the reduction in muscle strength suggest that the larger the muscle imbalance between internal and external shoulder rotators due
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