Sensitivity analysis of shoulder joint muscles by using the FEM model

Learning New Feedforward Motor Commands Based on Feedback Responses.

Introduction: To identify the effect of imagery exercises on activity of the shoulder muscles. Materials and method: A sample of 23 healthy participants (17 females and 6 males), with no history of shoulder injury, participated in the present study. Surface bipolar electrodes were applied over the supraspinatus, infraspinatus, posterior deltoid, middle deltoid, anterior deltoid, and pectoralis major. Participants performed six imagery exercises: flexion, extension, abduction, adduction, external rotation, and internal rotation. Root mean square of myoelectric activity of shoulder muscles was calculated for statistical analysis. The RMS during rest was used as an offset and also to normalize the activity of each muscle during imagery exercises. Results: Performing the imagery exercises resulted in significant activation of the shoulder muscles (P < 0.01). In the case of the supraspinatus muscle, significant difference (P< 0.05) was found among exercise types but no significant value was seen for infraspinatus muscle. In flexion, abduction, adduction, and internal rotation imagery exercises, the correlation observed between muscles activation was significant (P<0.01). Discussion: Supraspinatus highly activated in exercises including elevation of the arm. Activation of infraspinatus in all exercises suggest its important stability role in glenohumeral joint. Key words: Imagery exercise; Motor control; Re-education; Rotator cuff; Electromyography

This study is intended to provide a basic clinical data useful for preventing shoulder injuries related to occupation and curing them, by measuring the shoulder muscle activity of normal adults in an arm posture type of a wide shoulder joint angle, according to several differences of hand grip force.In order to examine the shoulder muscle activity during hand grips at a variety of intensity, according to the arm posture type, MVCs of all subjects were measured, and %MVCs of anterior deltoid, supraspinatus, the upper trapezius and infraspinatus at 0 degree, 90 degrees and 160 degrees of shoulder angle were yielded according to the grip force in an arm posture type, changing the maximum grip force into 30%, 50% and 90%, randomly.When measuring the hand grip at 30%, 50% and 70% of the maximum grip force to compare %MVC of each group depending on the arm posture type, there were no significant differences of muscle activity at 0 degree of shoulder angle among anterior deltoid, supraspinatus, the upper trapezius and infraspinatus, but there were significant differences of it among them at 90 degrees and 160 degrees of should angle(p<.001). According to the results of post-hoc test, also, anterior deltoid had the highest muscle activity, whereas the upper trapezius had the lowest muscle activity.

The aim of the present study was to investigate the patterns of shoulder muscle activation and joint torques during maximal effort eccentric contractions with shoulder extension, abduction, and diagonal movements on the isokinetic device. Participants in this investigation were nine men and four women with no history of shoulder injury or disorders. They all participated in overhead sports at least three days a week, and volunteered to participate in this study for shoulder isokinetic muscle strength testing. They performed eccentric muscle action with shoulder flexion, abduction, and diagonal movements at velocities of 60 rad·s−1 and 180 rad· s−1, which was followed alternately by passive shoulder flexion, abduction and diagonal movement at a velocity of 30 rad· s−1, and total range of motion was standardised to 90°. Electromyography (EMG) and torque values were calculated to every 10°, except for the start and end 5° during each task. During each test, the isokinetic force output and muscle activation were synchronised. EMG data were normalised by percentage of maximum voluntary isometric contraction (%MVIC). EMG signals were recorded by surface EMG from the anterior deltoid (AD), middle deltoid (MD), posterior deltoid (PD), upper trapezius (UT), middle trapezius (MT), and biceps brachii (BB) muscles during this test. All of the muscle patterns were significantly decreased at the last compared with the initial part during eccentric shoulder flexion movement, except for the BB muscle (P < 0.05). AD and BB muscles played a similar role when peak torque was generated under load during eccentric muscle action with varying shoulder movements. PD and UT muscle activities were significantly lower than the other muscle activities during eccentric contraction with shoulder flexion and abduction movements, and the PD and UT muscles played a significant role in conjunction with MD and MT muscles in varying degrees during eccentric contraction with shoulder diagonal movements at 180 rad·s−1 (P < 0.05). Our study demonstrated that MT muscle activity was greatly influenced when torque values showed a peak moment under load during maximum effort, eccentric contraction with shoulder abduction and diagonal movements. However, the MD, PD, UT, and MT muscle activities had no great influence when peak torque was generated under load during eccentric muscle action with shoulder diagonal movement at high velocity. The present study suggested that varying eccentric muscle activity patterns may be needed to investigate proper training and functional contributions of upper extremity muscles to stabilisation of the shoulder joint when peak torque was generated under load.

The effects of functional electrical stimulation on shoulder subluxation, arm function recovery, and shoulder pain in hemiplegic stroke patients

The purpose of this study was to calculate net shoulder (gleno-humeral) joint moments from inverse dynamics and to measure muscular activity from six shoulder muscles (supraspinatus, infraspinatus, middle deltoid, anterior deltoid, trapezius, and pectoralis major) during light weight-handling at two different displacements (horizontal and vertical) and frequencies (40 and 60 cycles/min), to simulate an occupational cervicobrachial working task (light weight displacement). Ten normal adult male subjects were asked to move a known weight, representing 15% of the maximal lifted weight, in both horizontal and vertical conditions at frequencies of 40 cycles/min and 60 cycles/min. Raw EMG signals from six shoulder muscles were recorded and synchronized with the cinematographic data during three trials of 6 s each. The raw EMG signals of each muscle were full wave rectified and filtered at 3 Hz. The linear envelope (LE EMG) signals were normalized by time (% cycle) and by amplitude (% MVC), and for the analysis of variance, the normalized LE EMG signals were integrated (IN LE EMG). The average shoulder angular velocities, joint moments, and moment powers were computed from cinematographical data. No significant differences were observed between both tasks for the supraspinatus, infraspinatus, and pectoralis major IN LE EMG data as well as for integrated normalized shoulder joint moment for the whole cycle of movement. IN LE EMG data from middle deltoid, anterior deltoid, and trapezius muscles were significantly higher (p less than 0.05) when performing the vertical displacement task for the whole cycle of movement. This muscular activity difference between vertical and horizontal tasks indicated that the vertical displacement conditions induced higher muscular loads on the shoulder than the horizontal weight displacement conditions, although the vertical displacements were approximately 15% longer than the horizontal displacements. The non-significant difference of IN LE EMG between frequencies obtained for all muscles indicated that neither frequencies induced more muscular activity.

Stability and instability of the glenohumeral joint: The role of shoulder muscles

Shoulder Pain

Estimations of shoulder muscle load are important in biomechanic and ergonomic research. We have studied shoulder muscle load in the trapezius (six subjects), deltoid (six subjects), infraspinatus (eight subjects), and supraspinatus (seven subjects) muscles with simultaneous intramuscular pressure (IMP) and intramuscular bipolar electromyography (EMG) recordings. For imposition of shoulder muscle load, the arm was positioned in abduction or flexion with different hand loads (0, 1, or 2 kg), or isometric force registrations were performed. The microcapillary infusion technique was used for IMP recordings. The IMP in the supra- and infraspinatus muscles were high compared with the trapezius and deltoid muscles in abducted arm positions. In all test situations, IMP and EMG gave a similar description of local muscle load. IMP at maximal voluntary contraction was highest in the supraspinatus and infraspinatus muscles. Both IMP and EMG in all four muscles showed an almost linear correlation to recorded isometric external force. The difference in IMP between shoulder muscles in the same arm position may be due to muscle anatomy, muscle function, and compliance of surrounding tissues. Because a high IMP may impede muscle blood flow, our findings may possibly explain the physiological stress on the rotator cuff muscles as compared with the deltoid and trapezius muscles in work with elevated arms.

The shoulder.

Individuals who use a manual wheelchair are at a high risk of developing long-term shoulder pain and impairment caused by increased demand and load on the shoulder during normal activities of daily living. Two main contributors to shoulder pain are overuse and shoulder muscle imbalance. Rehabilitation programs targeting shoulder pain suggest stretching anterior shoulder muscles and strengthening posterior shoulder muscles to promote balance and stability across the shoulder. Rowing-type exercises have been shown to successfully target the posterior muscles of the shoulder with evidence of decreased pain and increased shoulder strength after the completion of a functional electrical stimulation rowing intervention. In addition to reducing shoulder pain, it is crucial to identify methods and modes of exercise which are more widely accessible. Participation in physical activity provides physical, psychological, and social benefits. However, several barriers to physical activity have been reported in this population. Less than half of individuals with physical disabilities meet the American College of Sports Medicine's physical activity guidelines. The primary aim of this study was to analyze the biomechanics, as measured by scapulohumeral kinematics and muscle activation, and symmetry of the rowing stroke in an adapted setup in individuals who use a manual wheelchair for mobility. Muscle activity (electromyography) of four shoulder muscles (upper trapezius, lower trapezius, serratus anterior, and posterior deltoid) and 3D motion analysis of the humerus, scapula, and trunk were analyzed across three rowing conditions (adapted rowing ergometer, rowing ergometer from chair, standard row exercise) and between sides. We hypothesized that both adapted rowing ergometer conditions would lead to greater muscle activity than the standard rowing exercise and there would be no difference in humerus, scapula, or trunk kinematics among rowing conditions. It was also hypothesized that we would see symmetry across both muscle activity and kinematic measures. Upper extremity kinematics were symmetrical across rowing conditions with activity occurring below 90° of humeral elevation. Greater shoulder extension was seen at the finish position for the standard row exercise compared to the two ergometer rowing conditions. Overall, all three rowing conditions showed submaximal activation of the targeted muscles including increased lower trapezius activity without producing excessive upper trapezius activity. Findings from this study indicate that rowing is a highly repetitive low load activity occurring below 90° of humeral elevation. This suggests that rowing and rowing type activities have the potential to be an accessible form of exercise that facilitates increased shoulder strength and decreased should pain in individuals who use a manual wheelchair for mobility.

Shoulder muscle function in frozen shoulder syndrome patients following manipulation under anesthesia: A 6-month follow-up study

PURPOSE:To identify intermuscular EMG coherence patterns between the rotator cuff and deltoid muscles at different force levels. METHODS:Surface EMG electrodes were used to record activity from the anterior deltoid (AD), middle deltoid (MD), and infraspinatus (IS) muscles of the dominant shoulder in 7 healthy individuals (mean age ± SD = 19 ± 1, 6 females, 1 male). An intramuscular fine-wire EMG electrode was inserted into supraspinatus (SS). Participants performed 30s contractions of isometric shoulder abduction in the scapular plane at 30° at 25% (low-load), 50% (medium-load) and 75% (high-load) of maximum voluntary contraction with visual feedback of the force output. EMG amplitudes and coherence of each muscle pair in the common drive (0-5 Hz), physiological force tremor (5-12 Hz), beta (15-35 Hz), low-gamma (35-60 Hz) and high-gamma (60-100 Hz) bands were compared across the 3 force levels. RESULTS:EMG amplitudes of all muscles increased as force level increased (all p < 0.05). EMG coherence between IS and deltoid muscles increased as force level increased in the low-gamma band (p < 0.05). SS-IS coherence was also the highest during high-load task in the low-gamma band. These data indicate that additional neural drive with higher force levels stemming from subcortical origin likely mediate the increase in coherence between these muscles. However, SS-IS coherence during the medium and high load tasks were lower than that during the low-load task in the common drive band (p < 0.05), indicating that the increase in drive to these muscles for increasing force output is not targeted at common last-order neurons. Similarly, SS-AD coherence during the high-load task was lower than that during the medium-load task in the beta band (p < 0.05) and SS-AD and SS-MD was lower in the tremor band (p < 0.05) at higher force loads. The reduction in coherence between the SS and deltoid muscles and the SS and IS may serve to protect the humeral head from migrating superiorly at higher force loads. CONCLUSIONS:Increasing force output led to decreased coherence within the rotator cuff muscles and between supraspinatus and the deltoid muscles, but increased coherence between infraspinatus and the deltoid muscles. This likely serves as a protective mechanism against superior humeral head migration.

1. Arm movements toward a target involving motion at the shoulder and elbow joints and restricted to the sagittal plane were investigated. During some movements, target location changed suddenly, thus requiring an intentional correction of the trajectory by the human subject. 2. The reaction time to correct the trajectory was comparable to the reaction time to initiate the movement. 3. Coordination of arm and shoulder movements in this task was achieved by means of a reduction of the number of degrees of freedom of the movement. Such a simplification of the task took two forms. 4. Angular acceleration at the elbow and shoulder were linearly related to each other in the deceleratory phase of the movement, when the trajectory had to be corrected as well as when no such correction was required. 5. When the correction required an increase or decrease in flexor torque at the shoulder and elbow, electromyographic (EMG) activity in anterior deltoid and biceps increased or decreased simultaneously. When the correction demanded more activity in triceps and deltoid, these muscles were activated sequentially instead. It is concluded that rapid corrections of a movement involve the production of stereotyped patterns of activity in shoulder and elbow muscles.

Limitations of conservative therapy for massive rotator cuff tears-Relationship between recovery of shoulder elevation and deltoid muscle thickness