Scapulothoracic motion and muscle activity during the raising and lowering phases of an overhead reaching task

The effect of EMG biofeedback training on muscle activation in an impingement population

Subacromial impingement syndrome (SAIS) is one of the most diagnosed causes of pain in the upper extremity. The purpose of this study was to investigate muscle activity between asymptomatic and SAIS shoulders on the same subject while understanding the effectiveness of EMG biofeedback training (EBFB) on bilateral overhead movements. Ten participants (7 male), that tested positive for 2/3 SAIS clinical tests, volunteered for the study. Bilateral muscle activity was measured via electrodes on the upper trapezius (UT), lower trapezius (LT), serratus anterior (SA), and lumbar paraspinals (LP). Participants performed bilateral scapular plane overhead movements before and after EBFB. EBFB consisted of 10 bilateral repetitions of I, W, T, and Y exercises focused on reducing UT and increasing LT and SA activity. Prior to EBFB, no significant difference in muscle activity was present between sides. A significant main effect of time indicated that after EBFB both sides exhibited reduced UT activity at 60° (p = 0.003) and 90° (p = 0.036), LT activity was increased at all measured humeral angles (p < 0.0005), and SA muscle activity was increased at 110° (p = 0.001). EBFB in conjunction with scapular based exercise effectively alters muscle activity of asymptomatic and symptomatic scapular musculature.

Clavicular and scapular, but not spinal kinematics vary with scapular dyskinesis type during arm elevation and lowering in persons with neck pain

BACKGROUND

Scapular dyskinesis is often observed in patients with neck pain. However, it is unknown whether clavicular, scapular and spinal kinematics vary with different types of scapular dyskinesis during arm movement.

RESEARCH QUESTION

Are there differences in clavicular, scapular and spinal kinematics during unilateral arm elevation and lowering among neck pain patients presenting with (i) scapular winging, (ii) with dysrhythmia, (iii) with no scapular abnormality and (iv) healthy controls?

METHODS

Sixty participants with neck pain (20 in each group) and 20 asymptomatic controls were recruited. The 3D kinematic data were measured during unilateral arm elevation and lowering at 30°, 60°, 90°, and 120° in the scapular plane. A three-way mixed-effects ANOVA was used to determine the main effects (group, phase and angle) and the interactions between three independent variables on the kinematic data.

RESULTS

The neck pain group with scapular winging had decreased clavicular retraction and increased scapular internal rotation and anterior tilt compared to the other neck pain and control groups at all angles during both phases of arm movement (p < 0.01). The neck pain group with scapular dysrhythmia had decreased scapular upward rotation compared to all other groups (p < 0.01). Some alterations in the kinematics existed during the lowering phase compared to the raising phase for all groups (p < 0.05). Spinal kinematics were similar across all groups (p > 0.05).

SIGNIFICANCE

Specific patterns of clavicular and scapular kinematics were identified during arm movement relevant to the type of observed scapular dyskinesis in patients with neck pain. Such findings stand to inform more precise and relevant motor training in rehabilitation and improve understanding of the association between altered scapular kinematics and neck pain.

Assessing Smoothness of Arm Movements With Jerk: A Comparison of Laterality, Contraction Mode and Plane of Elevation. A Pilot Study

Measuring the quality of movement is a need and a challenge for clinicians. Jerk, defined as the quantity of acceleration variation, is a kinematic parameter used to assess the smoothness of movement. We aimed to assess and compare jerk metrics in asymptomatic participants for 3 important movement characteristics that are considered by clinicians during shoulder examination: dominant and non-dominant side, concentric and eccentric contraction mode, and arm elevation plane. In this pilot study, we measured jerk metrics by using Xsens^® inertial measurement units strapped to the wrists for 11 different active arm movements (ascending and lowering phases): 3 bilateral maximal arm elevations in sagittal, scapular and frontal plane; 2 unilateral functional movements (hair combing and low back washing); and 2 unilateral maximal arm elevations in sagittal and scapular plane, performed with both arms alternately, right arm first. Each arm movement was repeated 3 times successively and the whole procedure was performed 3 times on different days. The recorded time series was segmented with semi-supervised algorithms. Comparisons involved the Wilcoxon signed rank test (p < 0.05) with Bonferroni correction. We included 30 right-handed asymptomatic individuals [17 men, mean (SD) age 31.9 (11.4) years]. Right jerk was significantly less than left jerk for bilateral arm elevations in all planes (all p < 0.05) and for functional movement (p < 0.05). Jerk was significantly reduced during the concentric (ascending) phase than eccentric (lowering) phase for bilateral and unilateral right and left arm elevations in all planes (all p < 0.05). Jerk during bilateral arm elevation was significantly reduced in the sagittal and scapular planes versus the frontal plane (both p < 0.01) and in the sagittal versus scapular plane (p < 0.05). Jerk during unilateral left arm elevation was significantly reduced in the sagittal versus scapular plane (p < 0.05). Jerk metrics did not differ between sagittal and scapular unilateral right arm elevation. Using inertial measurement units, jerk metrics can well describe differences between the dominant and non-dominant arm, concentric and eccentric modes and planes in arm elevation. Jerk metrics were reduced during arm movements performed with the dominant right arm during the concentric phase and in the sagittal plane. Using IMUs, jerk metrics are a promising method to assess the quality of basic shoulder movement.

Physiotherapy Rehabilitation in Subjects Diagnosed with Subacromial Impingement Syndrome Does Not Normalize Periscapular and Rotator Cuff Muscle Onset Time of Activation

Clinicians suggest that rehabilitation of Subacromial Impingement Syndrome (SIS) should target improving movement patterns to ensure better clinical outcomes. Understanding changes in onset time of activation patterns and associated changes in clinical outcomes could improve our understanding of rehabilitation strategies. In this prospective longitudinal study, we examined neuromuscular firing patterns and clinical features before and after a standardized physiotherapy program in subjects diagnosed with SIS. Electromyography (EMG) recordings of eleven shoulder muscles were taken at the initial and discharge consultation in 34 male volunteers diagnosed with SIS. EMG recording was performed during flexion, scaption, and abduction at slow, medium, and fast speeds with a loaded (3 kg) and unloaded arm, as well as rotational motion, rotational strength, pain, and shoulder function. Completion of standardized shoulder physiotherapy program for SIS resulted in improvements in clinical outcomes. Resulted showed inconsistent differences of onset time of activation mainly in some of the periscapular muscles for all movements. No differences were seen on the EMG recordings for rotator cuff muscles. Differences in range of motion, strength and function were shown. Despite some changes in onset time of activation, this study was not able to demonstrate consistent changes of onset time of activation of the periscapular and rotator cuff muscles.

Scapular motion is accelerated in asymptomatic individuals with dyskinesis: An observational study

INTRODUCTION

Individuals with shoulder and upper extremity pathology often present with altered scapular motion. Few studies have looked at variations in scapular acceleration as a way of quantifying scapular motion. The purpose was to determine the effectiveness of wireless accelerometers for detecting changes in acceleration in individuals with scapular dyskinesis.

MATERIALS/METHODS

Twenty-seven asymptomatic college students (mean age 24 (SD ± 1.54), 65% female, 93% right handed) were visually screened for scapular dyskinesis using previously described criteria. Of the students recruited, fifteen students were determined to have scapular dyskinesis. After securing a wireless accelerometer (MyoResearch 3D DTS) on the dominate scapula, the participants performed five repetitions of standing scaption from 0 to 140°. Linear scapular accelerations along three orthogonal axes (frontal-y, transverse-z, and sagittal-x) were collected. Intraclass correlation coefficients (ICC_{3, k}) were used to determine the between day intra-rater reliability while a one-way analysis of variance was used to determine differences in acceleration between those with and without dyskinesis.

RESULTS

There was good between day intra-rater reliability for the average of all three axes (ICC = 0.79) and for the x and y axes (ICC > 0.78). Reliability was poor (ICC = 0.31) for the z-axis. There was a significant increase in overall acceleration of the scapula in those with dyskinesis (p = .039). There was also a significant increase in acceleration along the y-axis for those with dyskinesis (p = .003) but not for the other axes (p > .16).

CONCLUSION

Wireless accelerometers reliably quantify scapular acceleration in healthy individuals. In a healthy population with dyskinesis, the overall magnitude of scapular acceleration was greater when compared to a healthy group without dyskinesis.

Trapezius and serratus anterior muscle strength in violinists with unilateral neck pain

BACKGROUND

Weakness of the trapezius and serratus anterior (SA) muscle may be a risk factor for unilateral neck pain.

OBJECTIVE

This study examined the trapezius (upper, middle, and lower) and SA muscle strength ipsilateral and contralateral to the painful side in violinists with unilateral neck pain.

METHOD

Twenty-six female violinists with unilateral neck pain participated in this study. Participants reported the pain intensity and duration and completed the Neck Disability Index (NDI). The strengths of the upper (UT), middle (MT), and lower (LT) trapezius and SA muscles were measured using a handheld dynamometer. Paired t-test was used to compare the strength of the muscles between ipsilateral and contralateral to the painful side within subjects. The relationship between pain intensity, pain duration, and neck disability and strength deficit of the muscle was demonstrated by Pearson's correlation and Spearman's rank correlation.

RESULTS

The strengths of the UT, MT, LT, and SA muscles were significantly decreased on the painful side compared with the contralateral side (P< 0.05). Except for correlations between pain intensity and percent strength deficit of the UT and between pain duration and percent strength deficit of the MT (P< 0.05), there were no significant associations between pain intensity, pain duration, or NDI and the percent strength deficit of the UT, MT, LT and SA muscles (P> 0.05).

CONCLUSIONS

These results suggest that decreased UT, MT, LT, and SA muscle strength on the side of the pain should be considered in the rehabilitation of violinists with unilateral neck pain.

Shoulder muscle activation strategies differ when lifting or lowering a load

PURPOSE

Lowering a load could be associated with abnormal shoulder and scapular motion. We tested the hypothesis that lowering a load involves different shoulder muscle coordination strategies compared to lifting a load.

METHODS

EMG activity of 13 muscles was recorded in 30 healthy volunteers who lifted and lowered a 6, 12 or 18 kg box between three shelves. Kinematics, EMG levels and muscle synergies, extracted using non-negative matrix factorization, were analyzed.

RESULTS

We found greater muscle activity level during lowering in four muscles (+ 1-2% MVC in anterior deltoid, biceps brachii, serratus anterior and pectoralis major). The movements were performed faster during lifting (18.2 vs. 15.9 cm/s) but with similar hand paths and segment kinematics. The number of synergies was the same in both tasks. Two synergies were identified in ~ 75% of subjects, and one synergy in the others. Synergy #1 mainly activated prime movers' muscles, while synergy #2 co-activated several antagonist muscles. Synergies' structure was similar between lifting and lowering (Pearson's r ≈ 0.9 for synergy #1 and 0.7-08 for synergy #2). Synergy #2 was more activated during lowering and explained the greater activity observed in anterior deltoid, serratus anterior and pectoralis.

CONCLUSION

Lifting and lowering a load were associated with similar synergy structure. In 3/4 of subjects, lowering movements involved greater activation of a "multiple antagonists" synergy. The other subjects co-contracted all shoulder muscles as a unit in both conditions. These inter-individual differences should be investigated in the occurrence of shoulder musculoskeletal disorders.

Electromyographic biofeedback improves upper extremity function: a randomized, single-blinded, controlled trial

OBJECTIVE

To examine the effects of a 6-week surface electromyographic biofeedback intervention on the re-learning of upper extremity motor function in subjects with paretic upper extremity after stroke.

DESIGN

A randomized controlled trial.

SETTING

State Centre of Attention to Brain Injury, Madrid, Spain.

PARTICIPANTS

Thirty-eight participants in the sub-acute post-stroke stage were recruited and randomly allocated into either the surface electromyographic biofeedback (sEMG-BFB) or sham biofeedback (BFB) groups.

INTERVENTIONS

The sEMG-BFB group (n=19) received the intervention focused on re-learning scapulothoracic control during arm-reaching tasks involving shoulder abduction. The sham BFB group (n=19) received a sham intervention.

OUTCOME MEASURES

Upper extremity motor function assessed using the Fugl-Meyer Assessment-Upper Extremity Scale (66 points), the glenohumeral active range of motion, and the electromyographic amplitude signal of the middle deltoid and upper trapezius muscles were collected at baseline, after the intervention, and at the one-month follow-up.

RESULTS

Compared with the sham BFB group, the sEMG-BFB group experienced significant increases in upper extremity motor function after the intervention. The mean differences between groups were as follows: 4.79 points (95% CI 2.92 to 6.66) after the intervention; 6.55 points (95% CI 3.75 to 9.34) at the one-month follow-up; improved active range of motion 15.75 points (95% CI 6 to 30) after the intervention and electromyographic activity in the upper trapezius muscle changed in favour of the sEMG-BFB.

CONCLUSIONS

In the short term, a 6-week sEMG-BFB intervention effectively improved paretic upper limb motor function. Future research is needed to determine if the sEMG-BFB intervention has any long-term effects. Clinical trial number registration: NCT02974465 (ClinicalTrials.gov).

Relationship between scapular initial position and scapular movement during dynamic motions

Optimal scapular position and movement are necessary for normal function of the shoulder joint and it is essential to focus on scapula in the rehabilitation for shoulder disorders. The aim of this study was to discover the relationship between the scapular initial position and scapular movement during dynamic motions in healthy young men. Thirty-four men participated in this study. The scapular angles at initial position and in elevation and lowering during flexion and abduction were measured using an electromagnetic tracking device. The scapular movements from 30° to 120° during flexion and abduction were calculated. Spearman's rank correlation coefficients were used to analyze the relationship between the scapular initial position and scapular movements. For upward rotation and posterior tilt of the scapula, there were significant positive correlations between the scapular initial position and scapular movement during flexion and abduction. For internal rotation, there were significant positive correlations, except 90° in lowering phase and 120° in both phases. While the humeral elevation increased, the correlation coefficients tended to decrease. Except for the internal rotation our results clarified the interactions between the scapular initial position and scapular movement during dynamic motions in healthy young men. The tendency of the decrease in correlation coefficient with elevation angle was shown.

Scapular Kinematics by Sex Across Elevation Planes

Scapular kinematics are important indicators of dyskinesis, often suggesting underlying shoulder pathology, but the influence of sex is unknown. This study's objective was to examine scapular kinematics in healthy males and females. Positions of surface-mounted reflective markers were tracked during arm elevation movements in 0°/30°/40°/60°/90°/120° planes. Scapulothoracic rotations (protraction/retraction, medial/lateral rotation, posterior/anterior tilt) were calculated. ANOVA analysis evaluated main and interaction effects of sex, plane, phase, and elevation angle. Males and females had similar protraction/retraction and medial/lateral rotation kinematics; mean sex-related peak angle differences were 2.5°, 1.8° (raise [concentric]), respectively, and 2.9°, 2.7° (lower [eccentric]), respectively. Largest sex differences for mean peak angle occurred for posterior/anterior tilt at higher elevation angles (raise, 8.4°; lower, 8.5°). Elevation, plane, and phase were main effects for all scapular rotations (P < .001). Sex was not a main effect for any rotations. Sex × elevation interactions influenced protraction/retraction (P < .001) and posterior/anterior tilt (P < .001). Sex × plane (P ≤ .01) and sex × phase (P ≤ .002) interactions influenced all rotations. Lower posterior tilt for females compared to males at higher elevation angles could relate to higher female shoulder pathology incidence. Sex, plane, and phase are necessary components of uninjured scapular kinematics. Sex-specific differences provide insight into potential shoulder pathology etiology. These data provide a benchmark to assess pathological populations.

Muscle activity of upper and lower trapezius and serratus anterior during unloaded and maximal loaded shoulder flexion and extension

Altered scapular muscle activity is mostly described under unloaded and submaximal loaded conditions in impingement patients. However, there is no clear evidence on muscle activity with respect to movement phases under maximum load in healthy subjects. Therefore, this study aimed to investigate scapular muscle activity under unloaded and maximum loaded isokinetic shoulder flexion and extension in regard to the movement phase. Fourteen adults performed unloaded (continuous passive motion [CPM]) as well as maximum loaded (concentric [CON], eccentric [ECC]) isokinetic shoulder flexion (Flex) and extension (Ext). Simultaneously, scapular muscle activity was measured by EMG. Root mean square was calculated for the whole ROM and four movement phases. Data were analyzed descriptively and by two-way repeated measures ANOVA. CPM_Flex resulted in a linear increase of muscle activity for all muscles. Muscle activity during CON_Flex and ECC_Flex resulted in either constant activity levels or in an initial increase followed by a plateau in the second half of movement. CPM_Ext decreased with the progression of movement, whereas CON_Ext and ECC_Ext initially decreased and either levelled off or increased in the second half of movement. Scapular muscle activity of unloaded shoulder flexion and extension changed under maximum load showing increased activity levels and an altered pattern over the course of movement.

Bilateral changes in 3-D scapular kinematics in individuals with chronic stroke

BACKGROUND

Stroke can lead to altered scapular motion that may limit the ability to perform activities of daily living. The aims were to evaluate scapular kinematics of individuals with chronic stroke and the correlation with paretic arm function.

METHODS

Scapular kinematics was assessed in thirty-four individuals (Chronic stroke=17; controls=17) during arm elevation and lowering in scapular and self-selected planes, and during hair combing. The use of the paretic arm to perform activities of daily living was assessed by the Motor Activity Log (MAL-30). Scapular kinematics was compared among paretic and non-paretic arms, and controls. Correlation between scapular kinematics and MAL-30 was also verified.

FINDINGS

Paretic and non-paretic arms showed increased scapular internal rotation (p<0.05) during arm lowering in the scapular plane, and during arm elevation and lowering in the self-selected plane compared to controls. Increased internal rotation (p<0.05) was also found in the paretic arm during hair combing compared to controls. Increased scapular anterior tilt (p<0.05) was observed in the paretic arm during arm elevation while performing the activity of hair combing and during arm elevation and lowering in the scapular and self-selected planes compared to controls. The non-paretic arm showed increased anterior tilt (p<0.05) during arm elevation and lowering in self-selected plane compared to controls. No difference in scapular upward rotation among neither arms, nor correlation between scapular kinematics and MAL-30 were found (p>0.05).

INTERPRETATION

Individuals with chronic stroke showed bilateral scapular kinematics alterations. However, these alterations are not correlated with paretic arm function.

Differences in the activation and co-activation ratios of the four subdivisions of trapezius between genders following a computer typing task

The aim of this study was to provide a description of gender differences of the activation patterns of the four subdivisions of the trapezius (clavicular, upper, middle, lower) following a 60min computer work task. Surface EMG was collected from these subdivisions from 21 healthy subjects during bilateral arm elevation pre-/post- task. Subjects completed a standardized 60min computer work task at a standard, ergonomic workstation. Normalized activation and activation ratios of each trapezius subdivision were compared between genders and condition with repeated measures ANOVAs. The interaction effect of Gender×Condition for upper trapezius% activation approached significance at p=0.051with males demonstrating greater activation post-task. The main effect of Condition was statistically significant for% activation of middle and lower trapezius (p<0.05), with both muscles demonstrating increase activation post-task. There was a statistically significant interaction effect of Gender×Condition for the Middle Trapezius/Upper Trapezius ratio and main effect of Condition for the Clavicular Trapezius/Upper Trapezius ratio, with a decreased ratio post-typing. Gender differences exist following 60min of a low force computer typing task. Imbalances in muscle activation and activation ratios following computer work may affect total shoulder kinematics and should be further explored.

Effects of scapular taping in young adults with shoulder pain and scapular dyskinesis

OBJECTIVE

To assess the immediate effects of scapular taping on pain, isometric force, and the level of activation of several scapular girdle muscles in individuals with shoulder pain and scapular dyskinesis.

MATERIALS AND METHODS

Ten individuals with shoulder pain during arm elevation and scapular dyskinesis were included and evaluated by using a visual analogue scale (VAS), pressure algometry, dynamometry, and surface electromyography. All assessments were performed before and immediately after the application of scapular taping.

RESULTS

Scapular taping did not change the electromyographic activity of the upper trapezius muscle (p = 0.041, IC95%: -0.8256 to 10.8752). The positive effects of taping application were related to pain reduction (p = 0.025) and improvement in pressure algometry in the middle deltoid muscle (p = 0.020, IC95%:-1.8910 to -0.0490). Maximal isometric force did not change after the application of taping (flexo-abduction p = 0.4136, external rotation p = 0.4261). Significant correlations were noted between the VAS and pressure pain threshold (PPT) for the upper trapezius muscle (r = -0.6643, p = 0.0361) as well as for the PPT measures of the middle deltoid and infraspinatus muscles before (r = 0.9491, p = 0.0001) and after (r = 0.9006, p = 0.0004) the application of taping.

CONCLUSION

Scapular taping was not effective for inducing changes in the electromyographic activity of the upper trapezius, lower trapezius, and serratus anterior muscles, nor in altering the isometric force of shoulder flexo-abduction and external rotation. However, taping was effective at improving the pressure algometry values of the middle deltoid. Significant correlations between the pressure algometry of the middle deltoid and infraspinatus muscles, both before and after the application of scapular taping, were noted.

Shoulder Coordination During Full-Can and Empty-Can Rehabilitation Exercises

CONTEXT

Supraspinatus tear is a common rotator cuff injury. During rehabilitation, debate persists regarding the most appropriate exercises. Whereas shoulder coordination is part of normal arm function, it has been infrequently considered in the context of exercise selection.

OBJECTIVE

To assess shoulder-motion coordination during 2 common supraspinatus rehabilitation exercises and to characterize load and motion-direction influences on shoulder coordination.

DESIGN

Descriptive laboratory study.

SETTING

Motion-analysis laboratory. Patient or Other Participants :  Fifteen asymptomatic right-hand-dominant men (age = 26 ± 4 years, height = 1.77 ± 0.06 m, mass = 74.3 ± 7.7 kg).

INTERVENTION(S)

Full-can and empty-can exercises with and without a 2.27-kg load.

MAIN OUTCOME MEASURE(S)

We recorded motion with an optoelectronic system. Scapulohumeral rhythm and complete shoulder joint kinematics were calculated to quantify shoulder coordination. The effects of exercise type, load, motion direction, and humerothoracic-elevation angle on the scapulohumeral rhythm and shoulder-joint angles were assessed.

RESULTS

We observed multivariate interactions between exercise type and humerothoracic elevation and between load and humerothoracic elevation. Scapulohumeral rhythm increased by a mean ratio of 0.44 ± 0.22 during the full-can exercise, whereas the addition of load increased mean glenohumeral elevation by 4° ± 1°.

CONCLUSIONS

The full-can exercise increased the glenohumeral contribution, as hypothesized, and showed normal shoulder coordination. During the empty-can exercise, the increased scapulothoracic contribution was associated with a compensatory pattern that limits the glenohumeral contribution. Using loads during shoulder rehabilitation seems justified because the scapulohumeral rhythm is similar to that of unloaded arm elevation. Finally, motion direction showed a limited effect during the exercises in healthy individuals.

Specific kinematics and associated muscle activation in individuals with scapular dyskinesis

BACKGROUND

Knowledge of the kinematics and associated muscular activity in individuals with scapular dyskinesis may provide insight into the injury mechanism and inform the planning of treatment strategies. We investigated scapular kinematics and associated muscular activation during arm movements in individuals with scapular dyskinesis.

METHODS

A visual-based palpation method was used to evaluate 82 participants with unilateral shoulder pain. Scapular movements during arm raising/lowering movements were classified as abnormal single pattern (inferior angle prominence, pattern I; medial border prominence, pattern II; excessive/inadequate scapular elevation or upward rotation, pattern III), abnormal mixed patterns, or normal pattern (pattern IV). Scapular kinematics and associated muscular activation were assessed with an electromagnetic motion-capturing system and surface electromyography.

RESULTS

More scapular internal rotation was found in pattern II subjects (4°, P = .009) and mixed pattern I and II subjects (4°, P = .023) than in control subjects during arm lowering. Scapular posterior tipping (3°, P = .028) was less in pattern I subjects during arm lowering. Higher upper trapezius activity (14%, P = .01) was found in pattern II subjects during arm lowering. In addition, lower trapezius (5%, P = .025) and serratus anterior activity (10%, P = .004) were less in mixed pattern I and II subjects during arm lowering.

CONCLUSIONS

Specific alterations of scapular muscular activation and kinematics were found in different patterns of scapular dyskinesis. The findings also validated the use of a comprehensive classification test to assess scapular dyskinesis, especially in the lowering phase of arm elevation.

Motion of the shoulder complex in individuals with isolated acromioclavicular osteoarthritis and associated with rotator cuff dysfunction: part 2 - muscle activity

This study aimed to compare muscle activity in individuals with isolated acromioclavicular osteoarthritis (ACO), ACO associated with rotator cuff disease (ACO+RCD), and controls. Seventy-four participants (23 isolated ACO, 25 ACO+RCD, 26 controls) took part in this study. Disability was assessed with the Disabilities of the Arm, Shoulder and Hand (DASH) questionnaire. Muscle activity of the upper trapezius (UT), lower trapezius (LT), serratus anterior (SA), and anterior deltoid (AD) was collected during arm elevation in the sagittal and scapular planes. Pain during motion was assessed with the numerical pain rating scale. Analysis of the DASH, pain and kinematics were reported in part 1 of this study. For each muscle, separate 2-way linear mixed-model ANOVAs were performed to compare groups. ACO+RCD group had more UT and AD activity than the the isolated ACO and control other groups, more AD activity than the isolated ACO group during the ascending phase, and more AD activity than the ACO and control groups during the descending phase in both planes. Isolated ACO group had less SA activity than the control group only in the sagittal plane. Alterations in shoulder muscle activity are present in individuals with isolated ACO and with ACO+RCD and should be considered in rehabilitation.

Electromyographic study of neck muscle activity according to head position in rugby tackles

[Purpose] This study examined differences in neck muscle activity in two different head positions during tackles with the aim of contributing to the prevention of sports injuries. [Subjects] The subjects were 28 male high-school rugby players. [Methods] Two tackle positions were considered: a head-up position and a head-down position. Muscle activities of the sternocleidomastoid muscles and the upper, middle, and lower parts of the trapezius muscles were measured. [Results] Muscle activities of the sternocleidomastoid muscles and the right upper trapezius muscle were significantly increased in the head-up position, and the activity of the lower trapezius was significantly increased in the head-down position. [Conclusion] Tackling with the head-up position increases neck muscle activity and stability of the head and the neck.

Effects of different movement directions on electromyography recorded from the shoulder muscles while passing the target positions

PURPOSE

We compared electromyography (EMG) recorded from the shoulder joint muscles in the same position for different movement directions.

METHODS

Fifteen healthy subjects participated. They performed shoulder elevation from 0° to 120°, shoulder depression from 120° to 0°, shoulder horizontal adduction from -15° to 105°, and shoulder horizontal abduction from 105° to -15°. The target positions were 90° shoulder elevation in the 0°, 30°, 60°, and 90° planes (0°, 30°, 60°, and 90° positions). EMG signals were recorded from the supraspinatus (SSP) muscle by fine-wire electrodes. EMG signals from the infraspinatus (ISP), anterior deltoid, middle deltoid, and posterior deltoid muscles were recorded using active surface electrodes.

RESULTS

During elevation and horizontal abduction, the SSP showed significantly higher activity than that shown during depression and during horizontal adduction in the 0°, 30°, and 60° positions. During elevation, the ISP showed significantly higher activity than during depression and during horizontal adduction in the 90° position. During horizontal abduction, the ISP showed significantly higher activity than during depression in the 90° position.

CONCLUSIONS

When the movement tasks were performed in different movement directions at the same speed, each muscle showed characteristic activity.

Reliability and minimal detectable change in scapulothoracic neuromuscular activity

Alterations in scapular muscle activity, including excess activation of the upper trapezius (UT) and onset latencies of the lower trapezius (LT) and serratus anterior (SA) muscles, are associated with abnormal scapular motion and shoulder impingement. Limited information exists on the reliability of neuromuscular activity to demonstrate the efficacy of interventions. The purpose of this study was to characterize the reproducibility of scapular muscle activity (mean activity, relative onset timing) over time and establish the minimal detectable change (MDC). Surface electromyography (sEMG) of the UT, LT, SA and anterior deltoid (AD) muscles in 16 adults were captured during an overhead lifting task in two sessions, one-week apart. sEMG data were also normalized to maximum isometric contraction and the relative onset and mean muscle activity during concentric and eccentric phases of the scapular muscles were calculated. Additionally, reliability of the absolute sEMG data during the lifting task and MVIC was evaluated. Both intrasession and intersession reliability of normalized and absolute mean scapular muscle activity, assessed with intraclass correlation coefficients (ICC), ranged from 0.62 to 0.99; MDC values were between 1.3% and 11.7% MVIC and 24 to 135 mV absolute sEMG. Reliability of sEMG during MVIC was ICC = 0.82-0.99, with the exception of intersession upper trapezius reliability (ICC = 0.36). Within session reliability of muscle onset times was ICC = 0.88-0.97, but between session reliability was lower with ICC = 0.43-0.73; MDC were between 39 and 237 ms. Small changes in scapular neuromuscular mean activity (>11.7% MVIC) can be interpreted as meaningful change, while change in muscle onset timing in light of specific processing parameters used in this study is more variable.