Rate of EMG Rise and Rate of Force Development of Scapular Muscles

Study Overview
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Brief Summary
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The investigators will clarify rate of electromyography (EMG) rise and rate of force development in overhead athletes on scapular muscles, including upper trapezius, lower trapezius and serratus anterior. The correlation between rate of EMG rise and rate of force development will also be examined.

Detailed Description
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The contributing factor of scapular dyskinesis can be bony and joint-related issues, neurologic problems, soft tissue problems. Patient with thoracic kyphosis, pectoralis minor stiffness, long thoracic nerve injury, and so on can lead to scapular dyskinesis and further shoulder dysfunction. During shoulder movement, the neuromuscular control of the scapular muscles also play an important role. Previous studies found that participants with pattern 1 and 2 scapular dyskinesis had lesser lower trapezius (5%, P =.025) and serratus anterior activity (10%, P =.004), and higher upper trapezius activity (14%, P =.01) in pattern 2 participants during arm lowering compared to normal participants. Furthermore, the intervention focus on neuromuscular control can change the recruitment pattern of participants with scapular dyskinesis. Significant increases in activation of the middle and lower trapezius (MT: 4.9 ± 2.4% of the maximal voluntary isometric contraction (MVIC); LT: 10.2 ± 6.8% MVIC, p < 0.0 25) were found with conscious control in 3 exercises among the 3 dyskinesis groups, and increased serratus anterior activation (11.2 ± 4.8% MVIC, p < 0.0 25) was found in the concentric phase of side-lying external rotation in the pattern 1 and 1 + 2 groups. The studies show that the muscle recruitment is highly related to the scapular dyskinesis. However, there are some limitation in the previous studies which presented the outcome by EMG amplitude. First, no matter with or without intervention, previous studies fail to show difference between groups in some condition. Although, there are some difference in lowering phase, the results fail to show difference in elevation phase and some degree of lowering phase. Second, substantial cancellation of the EMG interference signal can occur. The positive and negative signal will be offset. Last, not only neural effect but also contractile effect will be captured. Contraction type, including concentric, eccentric or isometric, will occur in a movement, so the signal will be affected. As the result, another method to represent neuromuscular effect should be considered. The rate of EMG rise (RER; Formula: ΔEMG/Δtime) has been used to evaluate the rate of muscle activation in order to account for the neural factors that contribute to rate of force development (RFD; Formula: Δforce/Δtime). The onset (<75 ms) of a rapid contraction indicates a role for neural factors. Previous studies with RER outcome have been conducted to see the effect of pain, aging or training. It has been reported that RER reduce with pain and aging while increase after training, and better sensitivity to distinguish difference than peak EMG amplitude (PEMG). The significant difference is found in both upper trapezius and deltoid for RER but only in upper trapezius for PEMG. However, most of the studies about RER are conducted on lower extremity or female worker and no study conducted on athletes, not to mention athletes with scapular dyskinesis. The overhead sports are characterized with forced and rapid movement. The more sensitive and functional measurement of RER may detect the difference of overhead athletes with different type scapular dyskinesis. Therefore, the purposes of this study are to compare the RER, PEMG, RFD and peak force on scapular muscles (UT, LT, SA) among different types of scapular dyskinesis at 2 arm elevation angles (30, 90 degree). Additionally, to investigate the correlation between RER and RFD. The investigators hypothesize that overhead athletes with scapular dyskinesis will demonstrate significant lower RER and RFD, and there will be significant positive correlation between RER and RFD.

Official Title
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Rate of EMG Rise and Rate of Force Development of Scapular Muscles in Overhead Athletes With Different Types of Scapular Dyskinesis

Conditions
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Scapular Dyskinesis

Intervention / Treatment
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* Behavioral: different type of scapular dyskinesis


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Playing overhead sports for at least 1 year. Still active in training or competition. The frequency of training or game should be at least 2 times per week, 1 hour per time. Exclusion Criteria: Subjects with shoulder pain onset due to trauma, a history of shoulder fractures or dislocation, cervical radiculopathy, degenerative joint disease of the shoulder, surgical interventions on the shoulder, or inflammatory arthropathy. Visual analog scale (VAS) > 5 during movement in the experiment.

Ages Eligible for Study
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Minimum Age: 20 Years
Maximum Age: 40 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| type 1 scapular dyskinesis<br>type 1 scapular dyskinesis classified by dyskinesis classification test | Behavioral: different type of scapular dyskinesis<br>* rapid arm elevation to see the different of EMG rise and force development<br>|
| type 2 scapular dyskinesis<br>type 2 scapular dyskinesis classified by dyskinesis classification test | Behavioral: different type of scapular dyskinesis<br>* rapid arm elevation to see the different of EMG rise and force development<br>|
| type 3 scapular dyskinesis<br>type 3 scapular dyskinesis classified by dyskinesis classification test | Behavioral: different type of scapular dyskinesis<br>* rapid arm elevation to see the different of EMG rise and force development<br>|
| type 4 scapular dyskinesis<br>type 4 scapular dyskinesis classified by dyskinesis classification test | Behavioral: different type of scapular dyskinesis<br>* rapid arm elevation to see the different of EMG rise and force development<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Rate of EMG rise | Surface EMG electrodes (The Ludlow Company LP, Chocopee, MA) were placed after shaving and preparation with alcohol to decrease skin impedance (typically 10 kΩ or less). An impedance meter (Model F-EZM5, Astro-Med Inc., Ri, USA) will be used to measure impedance between the electrodes and skin over the muscle. Bipolar surface EMG electrodes with an interelectrode (center-to-center) distance of 20 mm will be placed upper trapezius, lower trapezius and serratus anterior of the dominant shoulder. Electrodes for upper trapezius were placed midway between acromion and the seventh spinous process of cervical vertebrae. The lower trapezius was palpated obliquely upward and laterally along the line between intersection of the spine of scapula and the seventh spinous process of thoracic vertebrae. Electrodes for serratus anterior was placed anterior to the latissimus dorsi and posterior to pectoralis major. The reference electrode was placed on the ipsilateral clavicle | Baseline | 
| rate of force development | The force-sensitive measurement system (FlexiForce ELFTM, New Taipei City, Taiwan, R.O.C.) will be used for force detection. It combines three single-point FlexiForce B201 sensors, one handle containing USB-interface electronics, and Windows-compatible software (Figure 2). Three circle sensors (diameter 9.53 mm; thickness 0.203 mm) are able to detect therange of force as low (4.4-111N), medium (111-667N) and, high level (667-4448N), respectively. This ensures that the various force during measurement can be measured by the appropriate sensor. When the sensor detects the force, the software will display the histogram, curve graph, or number of the force detected as the real-time bio-feedback. The sampling rate of the data collection is set at 200Hz. | Baseline | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Posterior displacement of the scapula | The modified scapulometer will be stationed at one side to measure the distance from the root of the spine (ROS) and the inferior angle (INF) of the scapula to the thoracic wall, respectively. Before conducting the test, two anatomic landmarks, ROS and INF, will be identified and marked. Then two parallel landmarks on the same level of the ROS and INF, approximately 1 cm medial to the scapular medial border, will be marked. The first rater slides the digital caliper anteriorly toward the parallel landmark until firm contact. Posterior displacement of the scapula will be recorded by the second rater based on the digital caliper. | Baseline | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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overhead athletes, electromyography