Shoulder Muscle Activity Research Articles

Interaction between hand span and different sizes of keyboards on EMG activity in pianists: An observational study

The availability of keyboards with reduced key width has been recently promoted as an ergonomic aid for small-handed pianists to overcome any potential physical disadvantages that may restrict their piano repertoire. However, a lack of biomechanical data exists to support whether reduced piano key size is effective in achieving this outcome. This research investigates the effect of playing on three different key width size pianos (5.5-inch octave, 6.0-inch octave and conventional size with 6.5-inch octave) on hand, arm and shoulder muscle activity levels according to the hand size of the pianists.Results indicate that piano key size affects the muscle activity levels of selected muscles. Furthermore, this effect of different key sizes changed according to the players’ hand spans. Small-handed pianists may benefit from using smaller-sized keyboards to reduce muscular exertion during performance. This investigation provides preliminary EMG data supporting the use of different size keyboards to improve the ergonomic fit according to the dimensions of individual pianists.

Delayed Anticipatory Muscle Activation in Rotator Cuff Tendinopathy.

Background:Previous research investigating rotator cuff (RC) tendinopathy has usually focused on pathoanatomy. The pathologic response to anticipatory postural adjustments (APAs) has not yet been investigated.Purpose/Hypothesis:To explore changes in APAs as detected by pre-emptive activation of shoulder muscles during ball catching. It was hypothesized that anticipatory muscle activation (AMA) would be present in the unaffected shoulder but delayed or absent in the affected shoulder in patients with RC tendinopathy.Study Design:Controlled laboratory study.Methods:This study included 21 RC tendinopathy patients with a mean age of 49.5 years. Patients were required to grab a ball embedded with an electromyography sensor when it dropped on their hand, and surface electromyography signals were recorded from the infraspinatus, upper trapezius, anterior deltoid, and biceps. The trials utilized 2 balls, weighing 200 g and 500 g. Each ball was used in 2 trials, 1 involving a number count preceding the ball drop (predictable) and the other involving a sudden drop (unpredictable). The onsets of AMA between the affected and unaffected limbs were compared.Results:Regardless of the experimental condition, significantly delayed AMA onsets were identified in all investigated muscles of the affected side compared with those of the unaffected side, except for the biceps muscle in the 500-g predictable trial. For the infraspinatus, the mean onset time in the 200-g predictable trial was –141.0 ± 60.2 ms on the affected side and –211.9 ± 67.1 ms on the unaffected side (P < .001); in the 200-g unpredictable trial this value was –139.5 ± 54.9 ms on the affected side and –199.5 ± 56.2 ms on the unaffected side (P < .001).Conclusion:Delayed AMA was observed in the affected shoulder compared with the unaffected shoulder in patients with RC tendinopathy, not only in the RC muscle but also in the periscapular and upper arm muscles. This may indicate that central hypoexcitability is partly responsible.Clinical Relevance:The basis for RC tendinopathy treatment should not be limited to the tendon pathoanatomy. Delayed AMA around the shoulder joint could provide insight into potential mechanisms related to the central nervous system.

A kinematic and electromyographic comparison of a Grammont-style reverse arthroplasty combined with a l'Episcopo transfer compared to a lateralized humeral component reverse for restoration of active external rotation.

To assess kinematic and electromyographic findings of two designs of reverse total shoulder arthroplasty (RTSA). We tested two hypotheses: (H1) Grammont-style (RTSA) with l'Episcopo tendon transfer gains similar postoperative kinematic findings of a lateralized humeral component RTSA without a tendon transfer; (H2) RTSA with lateralized humeral component induces earlier shoulder muscle activation during shoulder motion compared with standard Grammont prosthesis with l'Episcopo transfer. Twenty-five patients with a cuff tear arthropathy, pseudoparalysis, and a positive dropping sign were sequentially included. A Grammont-style RTSA with a l'Episcopo tendon transfer was implanted in 13 patients (medialized humerus and transfer group) and an on-lay curved-stem RTSA in 12 (lateralized humerus group). Constant score; the disabilities of the arm, shoulder, and hand (DASH) score; and active shoulder range of motion (flexion, abduction, external rotation, and internal rotation) were measured pre- and postoperatively. Upper limb kinematic and surface electromyography (EMG) (anterior and posterior deltoid; upper, middle, and lower trapezius; and the upper and lower latissimus dorsi muscles) were recorded during active range of motion. At > 24months of follow-up, the Constant and DASH scores and active shoulder range of motion improved in both groups (p < 0.0001). Internal rotation was significantly higher in the lateralized humerus group than in the medialized humerus and transfer group (p = 0.004). The dropping sign was found in 0/12 patients in the lateralized humerus group and in 5/13 patients in the medialized humerus and transfer group (p < 0.001). Kinematic findings were similar between groups (p = 0.286). A pattern of earlier muscle activation in the lateralized humerus group was found as compared to the transfer group as follows: (i) posterior deltoid during external rotation (p = 0.004); (ii) upper latissimus dorsi and middle and lower trapezius during flexion (p = 0.004, p = 0.005, and p = 0.042, respectively); (iii) lower latissimus dorsi during abduction (p = 0.016). RTSA with a lateralized humeral component provided similar active external rotation restoration to a Grammont-style RTSA with a l'Episcopo procedure in patients with a dropping sign. The posterior deltoid muscle underwent earlier activation during active external rotation in the lateralized humerus RTSA group as compared to the tendon transfer group. Our findings demonstrated the H1 and only partially demonstrated the H2 of the study.

Evaluation of two upper-limb exoskeletons during overhead work: influence of exoskeleton design and load on muscular adaptations and balance regulation.

Overhead works (OHW) are identified as a major risk factor for shoulder musculoskeletal disorders. The use of upper-limb exoskeletons (EXOUL) is emerging to address these challenges. This research tested the influence of EXOUL design and load on the upper-limb and postural muscles activity, and on the balance control, during OHW. This study compared two passive EXOUL, notably differing by the level of assistive torque delivered. Both EXOUL was examined in two load conditions (2 vs. 8kg). Twenty-nine volunteers performed a static OHW for each condition. Both EXOUL led to similar reductions in shoulder flexor muscle activity (12.3 ± 7.8% of RMSREF), compared to without equipment (29.0 ± 14.2% RMSREF). Both EXOUL resulted in a reduction in the activity of shoulder (3.6 ± 3.2% RMSREF) and wrist (2.4 ± 1.7% RMSREF) extensor muscles (4.9 ± 3.9 and 5.9 ± 6.1% RMSREF, respectively). The use of EXOUL led to reductions in back muscle activity, depending on the exoskeleton design (in% RMSREF, 12.9 ± 9.4 for EXO1, 22.8 ± 12.6 for EXO2 and 32.0 ± 18.4 without equipment). Wearing EXOUL induced changes in balance regulation, depending on both exoskeleton design and load condition. The increase of assistive torque was not associated with an increase in EXOUL performance. However, the exoskeleton design (mass, balance, and assistive torque) has to be suitable for the load handled during static OHW to optimize the effects of using an EXOUL on the postural muscles.

Ergonomic evaluation of ergonomically designed chalkboard erasers on shoulder and hand-arm muscle activity among college professors

Teaching professionals regularly use the chalk board eraser or duster throughout their life which leads to several unnoticed musculoskeletal disorders. The purpose of this study was to provide an alternate design for the existing Indian model chalk board eraser, because current eraser design causes noticeable amount of biomechanical load on the wrist, hand and shoulder region when its frequency of usage was high and repetitive. Initially, pilot study was conducted through an online modified Nordic questionnaire among 60 college professors to identify the risky regions of the body due to the use of existing chalk board eraser. This was followed by an experimental trial using surface Electromyography Sensors (sEMG) in which the muscle behaviour was evaluated during the chalkboard erasing process employing three newly designed dusters and a traditional duster. The results revealed that Model A designed with a large palm rest to align the palm and the forearm had better usability and the musculoskeletal distress was reduced when compared with the traditional duster. Whereas Model C designed with slip guards to improve the gripping forces was found to have better performance rating after Model A. Model B provided with separate handle was found to be the worst performer when compared with the conventional duster. Results suggested that providing an improved palm rest and slip guards such as grooves reduces the musculoskeletal distress.

Blood Flow Restriction Training for the Shoulder: A Case for Proximal Benefit

Background: Although blood flow restriction (BFR) is becoming increasingly popular in physical therapy and athletic training settings, little is known about the effects of BFR combined with low-intensity exercise (LIX) on muscles proximal to the site of occlusion. Hypothesis/Purpose: Determine whether LIX combined with BFR applied distally to the shoulder on the brachial region of the arm (BFR-LIX) promotes greater increases in shoulder lean mass, rotator cuff strength, endurance, and acute increases in shoulder muscle activation compared with LIX alone. We hypothesized that BFR-LIX would elicit greater increases in rotator cuff strength, endurance, and muscle mass. We also hypothesized that the application of BFR would increase EMG amplitude in the shoulder muscles during acute exercise. Study Design: Controlled laboratory study. Methods: 32 healthy adults were randomized into 2 groups (BFR group, 13 men, 3 women; No-BFR group, 10 men, 6 women) who performed 8 weeks of shoulder LIX (2 times per week; 4 sets [30/15/15/fatigue]; 20% maximum) using common rotator cuff exercises (cable external rotation [ER], cable internal rotation [IR], dumbbell scaption, and side-lying dumbbell ER). The BFR group also trained with an automated tourniquet placed at the proximal arm (50% occlusion). Regional lean mass (dual-energy x-ray absorptiometry), isometric strength, and muscular endurance (repetitions to fatigue [RTF]; 20% maximum; with and without 50% occlusion) were measured before and after training. Electromyographic amplitude (EMGa) was recorded from target shoulder muscles during endurance testing. A mixed-model analysis of covariance (covaried on baseline measures) was used to detect within-group and between-group differences in primary outcome measures (α = .05). Results: The BFR group had greater increases in lean mass in the arm (mean ± 95% CI: BFR, 175 ± 54 g; No BFR, –17 ± 77 g; P < .01) and shoulder (mean ± 95% CI: BFR, 278 ± 90 g; No BFR, 96 ± 61 g; P < .01), isometric IR strength (mean ± 95% CI: BFR, 2.9 ± 1.3 kg; No BFR, 0.1 ± 1.3 kg; P < .01), single-set RTF volume (repetitions × resistance) for IR (~1.7- to 2.1-fold higher; P < .01), and weekly training volume (weeks 4, 6-8, ~5%-22%; P < .05). Acute occlusion (independent of group or timepoint) yielded increases in EMGa during RTF (~10%-20%; P < .05). Conclusion: Combined BFR-LIX may yield greater increases in shoulder and arm lean mass, strength, and muscular endurance compared with fatiguing LIX alone during rotator cuff exercises. These findings may be due, in part, to a greater activation of shoulder muscles while using BFR. Clinical Relevance: The present study demonstrates that BFR-LIX may be a suitable candidate for augmenting preventive training or rehabilitation outcomes for the shoulder.

Methodological aspects of the acromiohumeral distance measurement with ultrasonography—Reliability and effects of extrinsic and intrinsic factors in overhead and non‐overhead athletes

AbstractIntroductionTo improve comparability and interpretation of acromiohumeral distance (AHD) measurements, consequences of varying methodological approaches and population specific effects have to be known. This study aimed to investigate the intra‐ and inter‐rater reliability of different AHD ultrasound image analysis approaches in asymptomatic overhead‐ and non‐overhead athletes. Furthermore, the impact of shoulder muscle activity as well as relationships between AHD and individual factors were examined in different measurement positions.MethodsIsometric shoulder strength, shoulder range of motion (ROM) and AHD were measured in 27 male and female participants (14 overhead athletes; 13 non‐overhead athletes, age = 27.8 ± 5.2 years).ResultsIntra‐rater reliability (ICC3,1 0.996) was excellent. Inter‐rater reliability for the AHD defined as shortest distance between the most infero‐lateral edge of the acromion and the most superior aspect of the humerus (ICC2,1 0.997) was minimally higher than for the AHD defined as perpendicular distance (ICC2,1 0.959). Increased shoulder muscle activity led to larger AHD reductions with abduction. Higher shoulder strength was associated with larger AHD, while larger shoulder ROM led to shorter AHD, dependent on measurement position and population.ConclusionWhile shoulder muscle activity and ROM had a pronounced effect on AHD, effects of shoulder strength and population appeared to be marginal.

Task-Oriented and Imitation-Oriented Movements in Virtual Reality Exercise Performance and Design.

This study investigated the influence of game features and practice type on human kinematic and muscular performance in a virtual reality exercise (VRE). Participants demonstrated changes in shoulder flexion angle and muscle activation under different virtual scenarios. Conventional VRE studies often compared the outcomes between an experimental group that underwent exercise in VR and a real-world exercise control group, whereas comparisons between VRE programs are lacking. Besides, the attributes of VREs received little attention. Thirteen able-bodied participants performed upper extremity exercise movements in immersive VR using a head-mounted display. Participants performed task-oriented and imitation-oriented movements with different game features. Shoulder muscle activity (the deltoid, supraspinatus, and infraspinatus) and shoulder motion were collected. Practice type (task-oriented, imitation-oriented) significantly influenced the flexion angle of the shoulder complex (F(1,11) = 9.53, p = .01), and the muscle activity of the supraspinatus (F(1,9) = 12.61, p = .006) and the infraspinatus (F(1,9) = 12.71, p = .006). Game features did not have a statistically significant effect on shoulder flexion angle or shoulder muscles' activations. Compared to imitation-oriented practice, task-oriented practice elicited more intensive shoulder movements and muscular efforts but also induced greater movement variations. Substantial differences across game features levels should be further investigated to have significant effects. This research may help guide the design of future VREs. For strength training or rehabilitation where intensive practice is required, task-oriented practice should be considered; for movement learning where movement consistency is required, imitation oriented practice should be adopted.

Line Hops and Side Hold Rotation Tests Load Both Anterior and Posterior Shoulder: A Biomechanical Study.

BackgroundClinical tests should replicate the stressful positions encountered during sport participation. Evaluating the kinetic and electromyographical demands of clinical tests enables clinicians to choose appropriate tests for specific sports.PurposeTo describe the shoulder forces and muscle activation levels during closed chain functional tests of Line Hops (LH) and Side Hold Rotation (SHR).Study DesignDescriptive biomechanical studyMethodsTen asymptomatic participants were examined in a university laboratory. Two functional tests were evaluated using three-dimensional video analysis and electromyography to measure shoulder forces, moments, and muscular activity levels.ResultsSHR produced a peak average posterior translation force of 4.84 N/kg (CI95 4.32-5.36N/kg) and a peak average anterior translational force of 1.57 N/kg (CI95 1.10-2.01N/kg). High levels of serratus anterior (98% maximum voluntary isometric contraction (MVIC) and infraspinatus (52 %MVIC) were recorded during SHR. LH produced a posterior translational force of 4.25 N/kg (CI95 3.44–5.06N/kg). High levels of serratus anterior (105 %MVIC) and infraspinatus (87 %MVIC) were recorded during the push off phase of this activity.ConclusionsLH and SHR placed large posterior translational forces that approached half of a person’s bodyweight on shoulder structures. SHR produced an anterior translation force at extremes of horizontal abduction placing approximately 18% of bodyweight on shoulder structures. The LH test required the serratus anterior to provide power to push the upper torso of the ground while both the serratus and the infraspinatus provides scapular and humeral stability, respectively.Level of Evidence4: Case series

Sensing and Control of a Multi-Joint Soft Wearable Robot for Upper-Limb Assistance and Rehabilitation

In the field of wearable robotics, there has been increased interest in the creation of soft wearable robots to provide assistance and rehabilitation for those with physical impairments. Compared to traditional robots, these devices have the potential to be fully portable and lightweight, a flexibility that may allow for increased utilization time as well as enable use outside of a clinical environment. In this letter, we present a textile-based multi-joint soft wearable robot to assist the upper limb, in particular shoulder elevation and elbow extension. Before developing a portable fluidic supply system, we leverage an off-board actuation system for power and control, with the worn components weighting less than half kilogram. We showed that this robot can be mechanically transparent when powered off, not restricting users from performing movements associated with activities of daily living. Three IMUs were placed on the torso, upper arm and forearm to measure the shoulder and elbow kinematics. We found an average RMSE of ~ 5 degrees when compared to an optical motion capture system. We implemented dynamic Gravity Compensation (GC) and Joint Trajectory Tracking (JTT) controllers that actively modulated actuator pressure in response to IMU readings. The controller performances were evaluated in a study with eight healthy individuals. Using the GC controller, subject shoulder muscle activity decreased with increasing magnitude of assistance and for the JTT controller, we obtained low tracking errors (mean ~ 6 degrees RMSE). Future work will evaluate the potential of the robot to assist with activities in post-stroke rehabilitation.

The effectivity of a passive arm support exoskeleton in reducing muscle activation and perceived exertion during plastering activities

The supportive effect of arm-support exoskeletons has been mainly studied for single postures or movements. The aim of this study is to analyse the effect of such an exoskeleton on shoulder muscle activity and perceived exertion, in six tasks of plasterers, each including multiple arm movements. The tasks of ‘applying gypsum’, ‘screeding’ and ‘finishing’ were performed at a ceiling and a wall, with exoskeleton (Exo) and without (NoExo). EMG was recorded of six muscles involved in upper arm elevation, four agonists and two antagonists, and plasterers rated their perceived exertion (RPE). In all tasks, the EMG amplitudes of three agonist muscles, Trapezius and Medial Deltoid, and Biceps Brachii, were lower in Exo vs NoExo, while the agonist, Anterior Deltoid, showed lower EMG values in Exo in most tasks. None of the antagonists (Triceps Brachii, Pectoralis Major) showed increased EMG values in the Exo condition. RPE’s were lower in Exo condition for all tasks, except for ‘applying gypsum to the wall’. Overall, the exoskeleton seems to reduce loads in realistic plastering tasks. Practitioner summary: Exoskeletons are an emerging technology in the field of ergonomics. Passive arm support exoskeletons have mainly been tested in lab studies using continuous overhead work, involving one posture or movement. However, in reality, working tasks generally involve multiple movements. This study investigates the effectiveness of an arm support exoskeleton in work that requires multiple arm movements, specifically in plastering. Muscle activity, as well as perceived exertion were both reduced when working with an exoskeleton. Abbreviations: Exo: with exoskeleton; NoExo: without exoskeleton; RPE: rated perceived exertion; EMG: electromyography; Trap: upper trapezius; AD: anterior deltoid; MD: medial deltoid; BB: biceps brachii; TB: triceps brachii; PM: pectoralis major; RPD: rated perceived discomfort; p50: 50th percentile; p90: 90th percentile; MVC: maximum voluntary contraction; GEE: generalised estimated equations

Chronic Neck Pain Affects Shoulder Muscle Activity and Postural Control During Functional Reach

Chronic neck pain may affect sensorimotor integration, which is critical for postural control. Accordingly, this study investigated whether individuals with chronic neck pain display altered muscle activation and postural control compared with those of healthy adults while performing functional reach tasks. Three-dimensional kinematic analyses and electromyographic analyses were performed. 20 individuals with chronic neck pain and twenty healthy adults were recruited. The reach distance, anterior displacements of the centers of mass and pressure, and activity of the cervical muscles were recorded during functional reach tasks. Compared with the healthy adults, the individuals with chronic neck pain showed significantly smaller anterior displacements of the centers of mass and pressure and reduced muscle activity of the upper trapezius muscle. However, no difference in the reach distance was observed between the two groups. It is speculated that a functional reach task may not be sensitive enough to detect changes in the postural control of individuals with chronic neck pain. For individuals with chronic neck pain, a combination of clinical measures and quantitative assessments of the centers of mass and pressure is suggested to facilitate the early detection of changes in postural control.

The Effects of IASTM Using Vibration Stimulation on Shoulder Muscle Activity, Flexibility and Pain of Chronic Shoulder Pain Patients

The Effects of IASTM Using Vibration Stimulation on Shoulder Muscle Activity, Flexibility and Pain of Chronic Shoulder Pain Patients

The comparison of the shoulder muscle activation in patients with rotator cuff tear under an abduction brace among the three postures

Background: Immobilization using an abduction brace is essential for the relaxation of the rotator cuff and scapular muscles and the prevention of a retear in patients with rotator cuff tear after arthroscopic rotator cuff repair (ARCR). However, thus far, the comparison of the scapular muscle activities has not been compared among different postures under an abduction brace in patients after ARCR. Objectives: The purpose of our study was to compare the scapular muscle activities among the supine position, sitting position, and walking under an abduction brace before and after ARCR Study Design: Observational, repeated measures study. Methods: Twelve patients with full-thickness rotator cuff tears were studied. The mean patient age was 64.7 years. The scapular muscle activations of the ipsilateral limbs were measured using surface electromyography in three postures: supine position, sitting position, and walking. The integrated electromyography relative values of the upper trapezius, anterior deltoid, middle deltoid, and biceps brachii were compared preoperatively and at two weeks after ARCR. Results: The trapezius, biceps brachii, and middle deltoid in the walking showed significantly higher integrated electromyography relative values than those in the supine position, preoperatively and at two weeks after surgery. The anterior deltoid in the sitting position had significantly higher integrated electromyography relative values than those in the supine position. Conclusions: Postures affected the scapular muscle activities in ARCR patients under an abduction brace. Understanding the influence of posture on the scapular muscle activity after ARCR will help rehabilitation accurately and appropriately.

THE RELATIONSHIP OF PAINFUL SHOULDER DEVELOPMENT IN HEMIPLEJIA WITH GLENOHUMERAL SUBLUXATION AND FUNCTIONAL STATE

Objective: The aim of the study is to determine the relationship between hemiplegic shoulder pain (HSP) and glenohumeral (GH) subluxation, to evaluate the factors that may affect the development of HSP and GH subluxation, and to determine the effects of HSP on functional independence and activities of daily living (ADL).&#x0D; Material and Method: Sixty-one hemiplegic patients who admitted to the stroke clinic were included in the study. Shoulder pain, frequency of subluxation, and spasticity were evaluated with anamnesis and clinical examination. Upper limb functions brunnstrom motor stage; Activities of daily living and independence were evaluated with Functional Independence Scale (FIM) and Modified Barthel Index (MBI).&#x0D; Results: The HSP was not associated with the duration of stroke, the Brunnstrom motor stage of the upper extremity, the presence of GH subluxation, or spasticity (p&gt; 0.05), but a statistically significant relationship was found between the limitation of shoulder abduction and flexion movements and the development of pain in the shoulder (p 0.05), but it was found to be significantly associated with the Brunnstrom motor stage of the upper extremity (p 0.05).&#x0D; Conclusion: In this study, the relationship between shoulder pain and GH subluxation was not determined, but the relationship between limitation of motion and HSP suggests possible soft tissue lesions, and in this respect, education for shoulder protection should be given importance in rehabilitation programs. Considering the relationship between GH subluxation and motor development, early activation of shoulder muscles should be emphasized in the rehabilitation program.

Shared internal models for feedforward and feedback control of arm dynamics in non-human primates.

Previous work has shown that humans account for and learn novel properties or the arm's dynamics, and that such learning causes changes in both the predictive (i.e., feedforward) control of reaching and reflex (i.e., feedback) responses to mechanical perturbations. Here we show that similar observations hold in old-world monkeys (Macaca fascicularis). Two monkeys were trained to use an exoskeleton to perform a single-joint elbow reaching and to respond to mechanical perturbations that created pure elbow motion. Both of these tasks engaged robust shoulder muscle activity as required to account for the torques that typically arise at the shoulder when the forearm rotates around the elbow joint (i.e., intersegmental dynamics). We altered these intersegmental arm dynamics by having the monkeys generate the same elbow movements with the shoulder joint either free to rotate, as normal, or fixed by the robotic manipulandum, which eliminates the shoulder torques caused by forearm rotation. After fixing the shoulder joint, we found a systematic reduction in shoulder muscle activity. In addition, after releasing the shoulder joint again, we found evidence of kinematic aftereffects (i.e., reach errors) in the direction predicted if failing to compensate for normal arm dynamics. We also tested whether such learning transfers to feedback responses evoked by mechanical perturbations and found a reduction in shoulder feedback responses, as appropriate for these altered arm intersegmental dynamics. Demonstrating this learning and transfer in non-human primates will allow the investigation of the neural mechanisms involved in feedforward and feedback control of the arm's dynamics.

Changes in Shoulder Muscle Activities Depending on Static and Dynamic Body Positions during Shoulder External Rotation Exercises Using Kinetic Chain Concept

Changes in Shoulder Muscle Activities Depending on Static and Dynamic Body Positions during Shoulder External Rotation Exercises Using Kinetic Chain Concept

Effect of Expertise on Shoulder and Upper Limb Kinematics, Electromyography, and Estimated Muscle Forces During a Lifting Task.

To highlight the working strategies used by expert manual handlers compared with novice manual handlers, based on recordings of shoulder and upper limb kinematics, electromyography (EMG), and estimated muscle forces during a lifting task. Novice workers involved in assembly, manual handling, and personal assistance tasks are at a higher risk of upper limb musculoskeletal disorders (MSDs). However, few studies have investigated the effect of expertise on upper limb exposure during workplace tasks. Sixteen experts in manual handling and sixteen novices were equipped with 10 electromyographic electrodes to record shoulder muscle activity during a manual handling task consisting of lifting a box (8 or 12 kg), instrumented with three six-axis force sensors, from hip to eye level. Three-dimensional trunk and upper limb kinematics, hand-to-box contact forces, and EMG were recorded. Then, joint contributions, activation levels, and muscle forces were calculated and compared between groups. Sternoclavicular-acromioclavicular joint contributions were higher in experts at the beginning of the movement, and in novices at the end, whereas the opposite was observed for the glenohumeral joint. EMG activation levels were 37% higher for novices but predicted muscle forces were higher in experts. This study highlights significant differences between experts and novices in shoulder kinematics, EMG, and muscle forces; hence, providing effective work guidelines to ensure the development of a safe handling strategy is important. Shoulder kinematics, EMG, and muscle forces could be used as ergonomic tools to identify inappropriate techniques that could increase the prevalence of shoulder injuries.

Strategies for controlling axial shoulder rotation change shoulder muscle activity during external rotation exercises

The infraspinatus muscle has a crucial role in shoulder stability. Although axial shoulder rotation is useful for selective activation of the infraspinatus, no study has examined the influence of exercise position on axial shoulder rotation during shoulder external rotation (ER) exercises. Thus, this study investigated the muscle activity in the infraspinatus, posterior deltoid, and middle trapezius during shoulder ER exercises performed with and without controlled axial shoulder rotation in 2 different positions. Twenty healthy subjects performed prone external rotation (PER) exercises with and without pressure biofeedback and seated external rotation (SITER) exercises with and without posterior humeral head gliding. Muscle activity during each ER exercise was measured using surface electromyography. Exercise strategy (P < .001) and position (P < .001) had a significant main effect on muscle activity in the infraspinatus and posterior deltoid. However, no significant interaction between strategy and position was observed. For muscle activity in the middle trapezius, strategy and position had a significant interaction effect (P = .014). Muscle activity in the infraspinatus increased significantly with the use of strategies to control axial shoulder rotation, whereas muscle activity in the posterior deltoid and middle trapezius decreased significantly. For all 3 muscles, greater activity was observed in the prone position than the seated position. We suggest that PER with pressure biofeedback can be useful to improve selective activation of the infraspinatus muscle while further eliciting infraspinatus muscle activity.

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.