Kinesiologic considerations for targeting activation of scapulothoracic muscles – part 2: trapezius

BackgroundThe trapezius is an extensive muscle subdivided into upper, middle, and lower parts. This muscle is a dominant stabilizer of the scapula, normally operating synergistically with other scapular muscles, most notably the serratus anterior. Altered activation, poor control, or reduced strength of the different parts of the trapezius have been linked with abnormal scapular movements, often associated with pain. Several exercises have been designed and studied that specifically target the different parts of the trapezius, with the goal of developing exercises that optimize scapular position and scapulohumeral rhythm that reduce pain and increase function.MethodsThis paper describes the anatomy, kinesiology, and pathokinesiology of the trapezius as well as exercises that selectively target the activation of the different parts of this complex muscle.ConclusionsThis review provides the anatomy and kinesiology of the trapezius muscle with the underlying intention of understanding how this muscle contributes to the normal mechanics of the scapula as well as the entire shoulder region. This paper can guide the clinician with planning exercises that specifically target the different parts of the trapezius. It is recommended that this paper be read as a companion to another paper: Kinesiologic considerations for targeting activation of scapulothoracic muscles – part 1: serratus anterior.     

Kinesiologic considerations for targeting activation of scapulothoracic muscles - part 1: serratus anterior

BackgroundThe serratus anterior (SA) is capable of a wide range of actions across the scapulothoracic joint. Furthermore, the lack of control, strength, or activation of this important muscle is believed to be associated with several painful conditions involving the shoulder complex. Studies and clinical intuition have therefore identified several exercises that selectively target the activation of the SA.MethodsThis paper reviews the anatomy, innervation, testing, and complex actions of the SA. In addition, this paper describes the classic signs and symptoms of weakness or reduced activation of the SA. Several exercises are described and illustrated that purportedly target the activation of the SA, with the intention of optimizing muscular control and encouraging pain free shoulder motion.ConclusionsThis review provides the theoretical background and literature-based evidence that can help explain the SA's complex pathokinesiology, as well as guide the clinician to further develop exercises that likely challenge the muscle. This paper is written along with a companion paper entitled: Kinesiologic considerations for targeting activation of scapulothoracic muscles: part 2: trapezius. Both papers prepare the reader to expand their pallet of exercises that target and challenge these two dominant muscles, with a goal of improving function of the shoulder for several painful conditions caused by their reduced or altered activation pattern.     

Use of unstable exercises in periscapular muscle activity: A systematic review and meta-analysis of electromyographic studies

BackgroundThe use of unstable surfaces has been proposed to increase the neuromuscular demand. This strategy has been adopted to generate an increase in the activity of periscapular muscles due to its role in the stabilization of the scapula. However, the influence of this instability on the EMG activity remains uncertain. The aim of this study was to analyze the effects of using unstable surfaces on the EMG activity of the periscapular muscles.MethodsA comprehensive search in the PubMed, EMBASE, SCIELO, Web of Science, SCOPUS, Cochrane and LILACS databases was undertaken from their year of inception up to December 2019. Studies which directly investigated the EMG activity of periscapular muscles in healthy individuals while performing exercises for the upper limbs in stable and unstable conditions.ResultsA total of 33 studies which evaluated a total of 678 healthy individuals were found according to the eligibility criteria. A meta-analysis identified that the EMG activity of the upper trapezius showed a trivial increase with the insertion of the unstable surface (P = 0.04; SMD = 0.14 [95%CI 0.00, 0.27]). No significant effects were observed on the middle trapezius (P = 0.10) and lower trapezius (P = 0.25). A decrease of the anterior serratus EMG activity with a small effect size was observed by implementing an unstable surface (P = 0.01; SMD = −0.21 [95%CI -0.36, −0.05]).ConclusionThe use of unstable surfaces generated a trivial increase in the upper trapezius activity, and a slight decrease in the anterior serratus activity. No effect was observed on the middle and lower trapezius.     

Scapular muscle imbalance: implications for shoulder pain and pathology

Abstract

Background: The scapula is important for normal shoulder function. The correct length, strength, and sequence of recruitment of the scapulothoracic muscles are important in controlling the movement of the scapula which must maintain an optimal position in relation to the elevating humerus. Changes in the action of scapulothoracic muscles may potentially affect alignment and forces and may contribute to glenohumeral joint pathology.

Objective: The purpose of this paper is to review the literature that associates abnormal scapulothoracic muscle function with shoulder joint pain and pathology.

Major findings: Shoulder impingement syndrome, superior labrum anterior to posterior (SLAP) lesions and multidirectional instability have all been associated with dysfunctional movement patterns of the scapula. It is not clear if the observed changes in scapular movements and muscular control are the result of or are the cause of these various pathologies at the shoulder joint. Alterations in the force production of the scapulothoracic musculature including all parts of the trapezius and serratus anterior muscles have been reported. Tightness in the pectoralis minor and/or in the posterior glenohumeral joint capsule may also affect movement due to a general anterior tilting of the scapula which impairs its ability to attain a normally upwardly rotated position.

Conclusions: The results of the investigations reviewed imply that appropriate assessment of the length, strength, and activation of all parts of the upper trapezius, serratus anterior, and pectoralis minor are important in the rehabilitation of patients with glenohumeral joint pathology.     

EMG activity of the serratus anterior and trapezius muscles during elevation and PUSH UP exercises

BackgroundElevation and push up (Pu) exercises are considered to be beneficial for the rehabilitation of shoulder complex pathology. Despite their clinical utility, there is a lack of evidence comparing scapulothoracic muscles recruitment during these exercises.ObjectiveTo evaluate the EMG activity of upper trapezius (UT), Lower Trapezius (LT), Upper Serratus anterior (USa) and Lower Serratus anterior (LSa) muscles during a variety of elevation and Pu exercises.MethodsThirteen healthy participants (non, athlete, male, mean ± standard deviation; age: 21.1 ± 1.8 years; height: 1.80 m ± 0.04; weight: 79 ± 12 kg) were assessed. EMG data was collected during Scaption, wall slide and elevation with external rotation (EleEr) with and without load. Pu classic, Pu plus (PuP) on stable/unstable surfaces and Pu with shoulder internal rotation were also assessed.ResultsUT had a significant higher activity during ‘Scaption load’ (p < .05) and LT in ‘EleEr load’ and ‘Scaption load’ (p < .05). USa and LSa had a significant higher activity on ‘PuP unstable surface’ and ‘PuP internal rotation’ compared to elevation exercises (p < .05). Scaption had greater activity ratio compared to the other exercises on UT/LT (p < .05). Pu variations had lower results in UT/USa and UT/LSa ratios compared to shoulder elevation exercises (p < .05).ConclusionsElevation exercises produce significant effects on upper and lower trapezius activation while Pu exercises on Sa muscles. Wall slide exercise notes the lowest activation in all muscles. A descending order of muscle activity during different variations of elevation and Pu exercises is provided in order to guide exercise selection in everyday clinical practice.     

Quantification of upper limb electromyographic measures and dysfunction of breast cancer survivors during performance of functional dynamic tasks

BackgroundUpper limb morbidities within the breast cancer population can interfere with completing daily life activities. Current knowledge of upper limb capabilities is limited; previous increases in muscle activation on the affected cancer side suggest this population works at a higher fraction of their capability. The purposes of this study were to describe upper limb capabilities and dysfunction of breast cancer survivors through muscle activation monitoring via surface electromyography and muscle-specific strength tests during functional tasks.MethodsFifty survivors performed 88 dynamic tasks (divided into range of motion-reach or rotate, activities of daily life and work tasks). Muscle activation was examined for functional and strength testing tasks.FindingsTotal muscle effort (summation of integrated electromyography across measured muscles) was up to 5.1% greater on the affected side during work tasks (p = 0.0258). Increased activations existed in posterior deltoid, supraspinatus, upper trapezius and serratus anterior (p < 0.05) for several tasks, including daily living tasks. Reduced activation occurred in affected pectoralis major sternal during all tasks (p < 0.0001–0.0032), and affected infraspinatus in all but daily living tasks (p = 0.0002–0.0328). The affected side infraspinatus, supraspinatus and upper trapezius muscles demonstrated significant reductions in targeted strength testing (p = 0.0001–0.0057).InterpretationBoth primary and secondary muscles (outside surgery and radiation fields) were affected. In general, this population works at higher levels of muscle effort for the affected side yet demonstrates weakness in strength testing, which may reflect tissue damage. Strengthening exercises for the posterior rotator cuff and upper trapezius may be the most beneficial.     

Analysis of the kinetic chain in asymptomatic individuals with and without scapular dyskinesis

BackgroundThis study measured strength of the trunk and hip, and compared Y Balance Test and Upper Quarter Y Balance Test in individuals without and with scapular dyskinesis. Strength and endurance of the scapulothoracic muscles were also assessed.MethodsForty-four individuals without shoulder pain were divided in 2 groups: without scapular dyskinesis (age 26.00, SD 4.10 years) and scapular dyskinesis (age 23.68, SD 4.20 years). Scapular dyskinesis was assessed by clinical observation of the scapular motion during arm elevation, and was classified as present or absent. A handheld dynamometer was used to measure the isometric strength of the trunk flexors and lateral flexors, hip extensors and abductors, lower trapezius, serratus anterior, and latissimus dorsi. Y and Upper Quarter Y Balance Tests were performed with the individual in single-limb and 3-point plank position, respectively. Endurance of the scapulothoracic muscles was assessed with the individuals in prone with the arm at 135° abduction. Independent t-test and Mann-Witney test were used for comparison between groups. A P < 0.05 was considered significant. Effect sizes between groups were also calculated.FindingsNo differences (P > 0.05) were demonstrated between groups for all variables. Moderate effect size (d ~ 0.40) was found for the trunk flexors and hip extensors, and endurance of the scapulothoracic muscles, whereas the scapular dyskinesis group showed less strength and endurance in relation to the group without dyskinesis.InterpretationStrength of the trunk flexors and hip extensors, and endurance of the scapulothoracic muscles seem to have influence in scapular dyskinesis in non-athletes without shoulder pain.     

Three-dimensional scapulothoracic motion during active and passive arm elevation

BACKGROUND: Scapulothoracic muscle activity is believed to be important for normal scapulothoracic motion. In particular, the trapezius and serratus anterior muscles are believed to play an important role in the production and control of scapulothoracic motion. The aim of this study was to determine the effects of different levels of muscle activity (active versus passive arm elevation) on three-dimensional scapulothoracic motion. METHODS: Twenty subjects without a history of shoulder pathology participated in this study. Three-dimensional scapulothoracic motion was determined from electromagnetic sensors attached to the scapula, thorax and humerus during active and passive arm elevation. Muscle activity was recorded from surface electrodes over the upper and lower trapezius, serratus anterior, anterior and posterior deltoid, and infraspinatus muscles. Differences in scapulothoracic motion were calculated between active and passive arm elevation conditions. FINDINGS: Scapular motion was observed during the trials of passive arm elevation; however, there was more upward rotation of the scapula, external rotation of the scapula, clavicular retraction, and clavicular elevation under the condition of active arm elevation. This was most pronounced for scapular upward rotation through the mid-range (90-120 degrees) of arm elevation. INTERPRETATION: The upper and lower trapezius and serratus anterior muscles have an important role in producing upward rotation of the scapula especially throughout the mid-range of arm elevation. Additionally, it appears that capsuloligamentous and passive muscle tension contribute to scapulothoracic motion during arm elevation. Assessment of the upper and lower trapezius and serratus anterior muscles and upward rotation of the scapula should be part of any shoulder examination.     

Muscle activation patterns in the scapular positioning muscles during loaded scapular plane elevation: The effects of Latent Myofascial Trigger Points

BackgroundLatent Myofascial Trigger Points are pain-free neuromuscular lesions that have been found to affect muscle activation patterns in the unloaded state. The aim was to extend these observations to loaded motion by investigating muscle activation patterns in upward scapular rotator muscles (upper and lower trapezius and serratus anterior) hosting Latent Myofascial Trigger Points simultaneously with lesion-free synergists for shoulder abduction (infraspinatus and middle deltoid). This approach allowed examination of the effects of these lesions on both their hosts and their lesion-free synergists in order to understand their effects on the performance of shoulder abduction.MethodsSurface electromyography was employed to measure the timing of onset of muscle activation of the upper and lower trapezius and serratus anterior (upward scapular rotators), infraspinatus (rotator cuff) and middle deltoid (abductor of the arm) initially without load and then with light (1–4 kg) dumbbells. Comparisons were made between control (no Latent Trigger Points; n = 14) and Latent Trigger Point (n = 28) groups.FindingsThe control group displayed a relatively stable sequence of muscle activation that was significantly different in timing and variability to that of the Latent Trigger Point group in all muscles except middle deltoid (all P < 0.05). The Latent Trigger Point group muscle activation pattern under load was inconsistent, with the only common feature being the early activation of the infraspinatus.InterpretationThe presence of Latent Trigger Points in upward scapular rotators alters the muscle activation pattern during scapular plane elevation, potentially predisposing to overuse conditions including impingement syndrome, rotator cuff pathology and myofascial pain.     

The effects of shoulder joint abduction angles on the muscle activity of the serratus anterior muscle and the upper trapezius muscle while vibrations are applied

[Purpose] The purpose of this study was to examine the ratio between the upper trapezius and the serratus anterior muscles during diverse shoulder abduction exercises applied with vibrations in order to determine the appropriate exercise methods for recovery of scapular muscle balance. [Subjects and Methods] Twenty-four subjects voluntarily participated in this study. The subjects performed shoulder abduction at various shoulder joint abduction angles (90°, 120°, 150°, 180°) with oscillation movements. [Results] At 120°, all the subjects showed significant increases in the muscle activity of the serratus anterior muscle in comparison with the upper trapezius muscle. However, no significant difference was found at angles other than 120°. [Conclusion] To selectively strengthen the serratus anterior, applying vibration stimuli at the 120° shoulder abduction position is considered to be appropriate.Key words: Serratus anterior, Upper trapezius, Vibration     

Modifying a shrug exercise can facilitate the upward rotator muscles of the scapula

Background

Scapular dyskinesis, characterised by drooping scapulae and reduced upward rotation, has been implicated in the presentation of a number of shoulder disorders. Traditionally, in shoulder rehabilitation programmes, the shrug exercise has been prescribed to facilitate upward rotation of the scapula by strengthening the upper trapezius muscle. The aim of this research was to compare muscle activation levels during the standard shrug and the upward rotation shrug in a normal and pathological population.

Methods

Surface electrodes recorded electromyographical activity from upper trapezius, middle trapezius, lower trapezius and serratus anterior muscles in 23 normal participants and 14 participants with multi-directional shoulder instability. Participants completed 10 trials of the standard shrug exercise at 0° of shoulder abduction and the upward rotation shrug exercise at 30° of shoulder abduction in the coronal plane. Muscle activity was expressed as a percentage of maximum voluntary isometric contraction.

Findings

The four muscles tested performed at a higher intensity during the modified shrug than the standard shrug. Upper trapezius and lower trapezius activity was significantly greater (P < 0.05) in both populations. Though for middle trapezius and serratus anterior muscles, the modified shrug was statistically significant only in the normal population, P = 0.031 and P = < 0.001 respectively.

Interpretation

The upward rotation shrug is a more effective exercise for eliciting muscle activity of the upper and lower trapezius than the standard shrug in a normal and multi-directional instability population. Clinically, the upward rotation shrug might be useful to address scapular dyskinesis involving drooping shoulders and reduced scapula upward rotation.     

Surface EMG during the Push-up plus Exercise on a Stable Support or Swiss Ball: Scapular Stabilizer Muscle Exercise

[Purpose] Scapular stabilizer strengthening exercise is crucial for shoulder rehabilitation. The purpose of this study was to compare two types of push-up plus exercises, on a stable and unstable bases of support, using surface electromyography (EMG), to suggest an effective shoulder rehabilitation program. [Subjects and Methods] Ten healthy men volunteered for this study. All volunteers performed two sets of push-up plus exercise (standard push up and knee push up) on stable and unstable bases of support. The muscle activities of five important scapular stabilizer muscles (upper trapezius, middle trapezius, lower trapezius, serratus anterior, latissimus dorsi) were recorded during the exercise. [Results] The upper trapezius showed greater mean electric activation amplitude in the scapular retraction posture than in the scapular protraction posture, and the serratus anterior showed greater mean electric activation amplitude in the scapular protraction posture than in the scapular retraction posture. The root-mean-square normalized EMG values of the muscles were greater during the exercise performed on the unstable support than those on the stable support. [Conclusion] The standard push-up plus exercise on an unstable base of support helps to increase muscle activity, especially those of the upper/middle trapezius and serratus anterior.Key words: Scapular stabilizer, Push-up plus, Surface EMG     

The Effects of Vibration Stimuli Applied to the Shoulder Joint on the Activity of the Muscles Around the Shoulder Joint

[Purpose] The present study compared the muscle activity of the upper trapezius with those of the serratus anterior and the lower trapezius when slings, unstable surfaces, were laterally vibrated, to examine the effects of vibration during sling exercises on shoulder stabilization muscles. [Methods] The subjects performed push-up exercises on a sling and maintained isometric contraction in the final stage, while vibration was manually administered to the rope of the sling during the isometric-contraction stage. Vibration within a range of 10 cm was delivered for five seconds at a frequency of 1 Hz in time with a metronome. Vibrations were applied for five seconds at 3 Hz and 3.5 Hz, respectively. [Results] The serratus anterior showed a significant differences between isometric contraction with vibration of 3 Hz and isometric contraction with vibration of 3.5 Hz. [Conclusion] The upper trapezius and the lower trapezius showed prominent changes in muscle activity at 3.5 Hz, and the serratus anterior showed prominent changes in muscle activity at 3 Hz and 3.5 Hz. Therefore, as vibration frequency increased, making the load-bearing surface more unstable, the recruitment of the upper trapezius, the lower trapezius, and the serratus anterior increased. To perform exercises that selectively strengthen the serratus anterior, the exercises should be performed at a vibration frequency of 3 Hz.Key words: Vibration, Shoulder joint, Muscle activity     

Evidence for increased neuromuscular drive following spinal manipulation in individuals with subacromial pain syndrome

BackgroundThoracic spinal manipulation can improve pain and function in individuals with shoulder pain; however, the mechanisms underlying these benefits remain unclear. Here, we evaluated the effects of thoracic spinal manipulation on muscle activity, as alteration in muscle activity is a key impairment for those with shoulder pain. We also evaluated the relationship between changes in muscle activity and clinical outcomes, to characterize the meaningful context of a change in neuromuscular drive.MethodsParticipants with shoulder pain related to subacromial pain syndrome (n = 28) received thoracic manipulation of low amplitude high velocity thrusts to the lower, middle and upper thoracic spine. Electromyographic muscle activity (trapezius-upper, middle, lower; serratus anterior; deltoid; infraspinatus) and shoulder pain (11-point scale) was collected pre and post-manipulation during arm elevation, and normalized to a reference contraction. Clinical benefits were assessed using the Pennsylvania Shoulder Score (Penn) at baseline and 2–3 days post-intervention.FindingsA significant increase in muscle activity was observed during arm ascent (p = 0.002). Using backward stepwise regression analysis, a specific increase in the serratus anterior muscle activity during arm elevation explained improved Penn scores following post-manipulation (p < 0.05).InterpretationThoracic spinal manipulation immediately increases neuromuscular drive. In addition, increased serratus anterior muscle activity, a key muscle for scapular motion, is associated with short-term improvements in shoulder clinical outcomes.     

Ultrasound imaging with speckle tracking of cervical muscle deformation and deformation rate: Isometric contraction of patients after anterior cervical decompression and fusion for cervical disc disease and controls

There is currently a lack of information regarding neck muscle activity during specific exercises. The purpose of the present study was to investigate deformation and deformation rate in different layers of dorsal and ventral neck muscles during isometric neck muscle contraction in individuals after anterior cervical decompression and fusion and in healthy controls. This study included 10 individuals (mean age 60 years; SD 7.1) with a verified, long-standing neck disorder and 10 healthy, age- and sex-matched controls. Ultrasonography and post-process speckle tracking analysis was used to investigate the degree and the rate of neck muscles motions at the C4 segmental level during sub-maximal, isometric resistance of the head in a seated position. None of the analyses performed showed significant differences between groups (p > 0.05). In the dorsal muscles, both groups exhibited a higher deformation rate in the multifidus than in the trapezius, splenius, and semispinalis capitis (p ≤ 0.01). In the neck disorder group, the multifidus also showed a higher deformation rate compared to the semispinalis cervicis (p = 0.02). In the ventral muscles of patients with neck disorders, the longus colli had a higher deformation rate than the sternocleidomastoid (p = 0.02). Among the healthy controls, the multifidus showed a higher degree of deformation (p = 0.02) than the trapezius. In conclusion, our results showed no significant differences between the two groups in mechanical neck muscle activation. Larger studies with different exercises, preferably with a standardized measure of resistance, are needed to investigate whether patients and controls show differences in deformation and deformation rates in neck muscles.     

Influence of reducing anterior pelvic tilt on shoulder posture and the electromyographic activity of scapular upward rotators

BackgroundModifications of posture in a segment may influence the posture of adjacent and nonadjacent segments and muscular activity. The spine–shoulder and spine–pelvis relationships suggest that the pelvis may influence shoulder posture.ObjectiveTo investigate the effect of the active reduction of the anterior pelvic tilt on shoulder and trunk posture during static standing posture and on the electromyographic activity of the scapular upward rotators during elevation and lowering of the arm.MethodsThirty-one young adults were assessed in a relaxed standing position and a standing position with 30% active reduction of the anterior pelvic tilt. The pelvic tilt, trunk posture, and forward shoulder posture during the static standing posture and the electromyographic activity during elevation and lowering of the arm were assessed.ResultsPaired t-tests indicated that the active reduction of the anterior pelvic tilt reduced the trunk extension (MD = 1.09; 95%CI = −2.79 to −1.03). There were no effects on the forward shoulder posture (MD = 0.09; 95%CI = −0.92 to 1.09). Repeated measures of analyses of variance indicated an increase in lower trapezius electromyographic activity (MD = 3.6; 95%CI = 1.28 to 5.92). There was a greater reduction in upper trapezius activity after pelvic tilt reduction during arm elevation (MD = 1.52%; 95%CI = −2.79 to −0.25) compared to that during the lowering phase. There were no effects of pelvic tilt reduction on the electromyographic activity of the serratus anterior (MD = 3.26; 95%CI = −3.36 to 9.87).ConclusionThe influence of pelvic posture on the trunk posture and lower trapezius activation should be considered when assessing or planning exercise for individuals with shoulder or trunk conditions.     

Scapular Muscle Activity in Overhead Athletes With Symptoms of Secondary Shoulder Impingement During Closed Chain Exercises

Tucker WS, Armstrong CW, Gribble PA, Timmons MK, Yeasting RA. Scapular muscle activity in overhead athletes with symptoms of secondary shoulder impingement during closed chain exercises.

Objective

To determine the amount of muscle activation in 4 scapular muscles in overhead athletes with and without a history of secondary shoulder impingement, during 3 upper extremity closed chain exercises.

Design

One-between (group), one-within (exercise) repeated measures.

Setting

Controlled laboratory study.

Participants

Overhead athletes (n=15; mean age ± SD, 21.0±2.5y; mean height ± SD, 176.0±7.8cm; mean weight ± SD, 76.1±13.4kg) demonstrating with symptoms of shoulder impingement and overhead athletes (n=15; mean age ± SD, 20.4±3.8y; mean height ± SD, 174.1±9.7cm; mean weight ± SD, 73.3±11.7kg) with no shoulder pathologies.

Interventions

Subjects completed 5 individual trials of a standard push-up, a push-up on an unstable surface, and a revolution on a shoulder rehabilitation device while electromyography (EMG) recorded muscle activity of the serratus anterior, upper trapezius, middle trapezius, and lower trapezius.

Main Outcome Measures

The mean EMG data for the 4 muscles from the standard push-up, push-up on an unstable surface, and shoulder rehabilitation device trials were normalized as a percentage of a maximum voluntary isometric contraction for each muscle.

Results

There was a statistically significant interaction for the middle trapezius (F_2,56=3.856; P=.027). The shoulder impingement push-up on an unstable surface (33.76%±26.45%) had significantly greater activation compared with the shoulder impingement standard push-up (25.88%±13.76%), the shoulder impingement shoulder rehabilitation device (9.40%±5.86%), and the nonpathology push-up on an unstable surface (19.49%±7.73%). The shoulder impingement standard push-up had significantly greater activation compared with the shoulder impingement shoulder rehabilitation device and nonpathology standard push-up (17.99%±7.31%). The nonpathology standard push-up and nonpathology push-up on an unstable surface had significantly greater activation compared with the nonpathology shoulder rehabilitation device (7.95%±4.30%).

Conclusions

These results suggest that the muscle activation of the middle trapezius differs in overhead athletes with a history of secondary shoulder impingement compared with those who lack this history during closed chain exercise, as well as within the 3 closed chain exercises. The levels of muscle activation of the serratus anterior and upper trapezius during these closed chain exercises were similar between the 2 groups. These results support the use of closed chain exercises in the rehabilitation process of overhead athletes with secondary shoulder impingement. However, clinicians should consider the muscle(s) of interest when selecting an exercise.     

Determining safe teaching board heights through electromyographic analysis of the shoulder muscles

BackgroundAdjustable teaching boards have been recommended as an ergonomic practice geared at reducing the incidences of teaching-related shoulder musculoskeletal disorders among teachers. However, there are no standards guiding choice of appropriate teaching board heights. This study was aimed at evaluating shoulder muscle activities in response to five teaching board heights.MethodsThirty participants performed writing activities on five different board heights (Diff10 = standing height minus 10% of standing height; NormH = participant's standing height; Sum10 = standing height plus 10% of standing height; Sum20 = standing height plus 20% of standing height; Sum25 = standing height plus 25% of standing height). Electromyographic analysis of the anterior deltoid (AD), upper trapezius (UT), serratus anterior (SA) and pectoralis major (PM) muscles were performed simultaneously during each task. Data were analyzed with one-way ANOVA and independent T-test at p < 0.05.ResultsSum20 board height significantly (p < 0.001) elicited the highest activities in the AD (19.35 ± 11.26%) and UT (29.06 ± 29.53%) muscles while SA (20.37 ± 10.87%) and PM (20.86 ± 12.17%) muscles were most active at Sum25 board height. SA and PM muscles progressively increased with increasing board heights while AD and UT muscles showed alternating patterns of activation at increasing board heights. For safe ergonomic practices, recommended teaching board heights should be within the range of NormH and Sum10.ConclusionExtremely high or low teaching boards have tendencies of inducing musculoskeletal shoulder discomforts.