Abstract
BackgroundWhile cortical representations of intrinsic hand muscles have been extensively studied in healthy individuals, little is known about the representation of proximal upper limb muscles. Improving our understanding of normal shoulder function is important, given that shoulder musculoskeletal disorders affect approximately 20% of the population and are suspected to involve changes in central motor representations. The purpose of the study is to describe the motor representation (motor evoked potentials (MEP) amplitude at the hotspot, map area, normalized map volume and center of gravity) of the infraspinatus muscle in healthy individuals, and to explore the potential influence of hand dominance on this representation (i.e. symmetry of the excitability and of the location of motor map between sides), as well as the effect of age and gender on motor excitability.ResultsFifteen healthy participants took part in this study. No significant asymmetry between sides was observed for motor excitability (p = 0.14), map area (p = 0.73) and normalized map volume (p = 0.34). Moreover, no side x intensity interaction was found (p = 0.54), indicating similar stimulus response properties. No difference between sides was found in the location of infraspinatus motor representation, either in the mediolateral or anteroposterior axis (p > 0.10). Neither age nor gender influenced aMT (p > 0.58) or MEP size (p > 0.61).ConclusionsAs the cortical representation of infraspinatus muscles was found to be symmetric between sides, both in terms of excitability and location, comparisons between the intact and affected side could be performed in clinical studies, regardless of whether the dominant or non-dominant side is affected. The next step will be to characterize corticospinal excitability and map parameters in populations with shoulder disorders.
Highlights
While cortical representations of intrinsic hand muscles have been extensively studied in healthy individuals, little is known about the representation of proximal upper limb muscles
The purpose of the current study is to describe the motor representation of the infraspinatus muscle in healthy individuals, and to explore the potential influence of hand dominance on this representation, as well as the effect of age and gender on motor excitability
No significant asymmetry in motor excitability was observed between sides
Summary
While cortical representations of intrinsic hand muscles have been extensively studied in healthy individuals, little is known about the representation of proximal upper limb muscles. The rotator cuff (RC) is one of the most important muscle groups for shoulder function as it provides dynamic stability at the glenohumeral joint [1]. It is made of four muscles, the supraspinatus, infraspinatus, teres minor and subscapularis. The infraspinatus is a critical muscle for shoulder stability It is one of the primary agonists of glenohumeral lateral rotation. Individuals with shoulder disorders have been known to present alterations in the infraspinatus EMG activity during arm elevation [3,4]. The infraspinatus is an essential muscle to assess in populations with impaired shoulder function
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