Sex differences in torque steadiness, accuracy and activation of the shoulder girdle muscles during isometric shoulder scaption.

Females present more neck/shoulder musculoskeletal disorders and have different activation strategies of the shoulder girdle muscles than males. However, the sensorimotor performance and potential sex differences are still largely unexplored. The aim of this study was to investigate sex differences in torque steadiness and accuracy during isometric shoulder scaption. We also examined the amplitude and variability of the activation of the trapezius, serratus anterior (SA), and anterior deltoid muscles during torque output evaluation. Thirty-four asymptomatic adults (17 females) participated. Torque steadiness and accuracy were evaluated during submaximal contractions at 20 % and 35 % of peak torque (PT). There was no sex difference in torque coefficient of variation, but females had significantly lower torque standard deviation (SD) values than males at the two intensities evaluated (p < 0.001) and lower torque median frequency values compared to males, regardless of intensity (p < 0.01). Females had significantly lower absolute error values than males for torque output at 35 %PT (p < 0.01) and lower constant error values compared to males, regardless of intensity (p = 0.01). Females had significantly higher muscle amplitude values than males, except for SA (p = 0.10) and in general, females showed higher muscle activation SD values compared to males (p < 0.05). Females may require more complex muscle activation patterns to achieve a more stable and accurate torque output. Therefore, these sex differences may reflect control mechanisms that may also be at play when explaining the greater risk of neck/shoulder musculoskeletal disorders in females than males.

What factors contribute to the Scapular Assistance Test result? A classification and regression tree approach.

The aim of this study was to determine predictive factors related to the Scapular Assistance Test in individuals with shoulder pain during arm elevation, and to analyze how these predictors interact in a nonlinear manner to discriminate the result of a positive and negative Scapular Assistance Test. Eighty-four individuals with shoulder pain with positive (n = 47, average age 38.4 years) and negative (n = 37, average age 37.8 years) Scapular Assistance Test completed the study. Demographic data, affected shoulder, pain duration, pain at rest, angular onset of pain, scapular dyskinesis, serratus anterior and lower trapezius muscle strength, Disabilities of Arm, Shoulder and Hand questionnaire and Pain Catastrophizing Scale were assessed in all participants. The Classification and Regression Tree analysis was used to determine which factors would predict the occurrence of a positive or negative Scapular Assistance Test and possible interactions among them. The resulting tree presented seven levels that combine the following variables: angular onset of pain, presence of scapular dyskinesis, pain catastrophizing, serratus anterior and lower trapezius muscle strength. The angular onset of pain during arm elevation was the main predictor of a positive Scapular Assistance Test selected by the Classification and Regression Tree. This study indicates that the Scapular Assistance Test result may be explained not only by biomechanical variables, but also by psychological factors. Disability of the upper limbs does not seem to contribute to the Scapular Assistance Test result.

Electromyographic analysis of the serratus anterior and upper trapezius in closed kinetic chain exercises performed on different unstable support surfaces: a systematic review and meta-analysis.

Background: Multiple investigations have compared the electromyographic (EMG) activity of the scapular muscles between stable and unstable support surfaces during the execution of closed kinetic chain exercises. However, these comparative analyses have grouped different unstable surfaces (wobble board, BOSU, therapeutic ball, and suspension equipment) into a single data pool, without considering the possible differences in neuromuscular demand induced by each unstable support surface. This study aimed to analyze the individual effect of different unstable support surfaces compared to a stable support surface on scapular muscles EMG activity during the execution of closed kinetic chain exercises. Methodology: A literature search was conducted of the Pubmed Central, ScienceDirect and SPORTDiscus databases. Studies which investigated scapular muscles EMG during push-ups and compared at least two support surfaces were included. The risk of bias of included articles was assessed using a standardized quality assessment form for descriptive, observational and EMG studies, and the certainty of the evidence was measured with the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach. A random-effects model was used to calculate effect sizes (ES, Hedge's g). Results: Thirty studies were selected in the systematic review. Of these, twenty-three low-to-high quality studies (498 participants) were included in the meta-analysis. The main analyzes revealed, in decreasing order, greater UT EMG activity during push-ups performed on suspension equipment (ES = 2.92; p = 0.004), therapeutic ball (ES = 1.03; p < 0.001) and wobble board (ES = 0.33; p = 0.003); without effect on the BOSU ball. In addition, no effect was observed for SA on any unstable device. The certainty of the evidence ranged from low to very low due to the inclusion of descriptive studies, as well as high imprecision, inconsistency, and risk of publication bias. Conclusion: These findings could be applied in scapular muscles strengthening in healthy individuals. The use of suspension equipment achieves higher UT activation levels. Conversely, the use of any type of unstable devices to increase the activation levels of the SA in shoulder musculoskeletal dysfunctions is not recommended. These conclusions should be interpreted with caution as the available evidence showed a low to very low certainty of evidence, downgraded mostly by inconsistency and imprecision.

Scapulothoracic muscle activity during kinetic chain variations of a prone elevation exercise.

BACKGROUND: Scapular rehabilitation exercises should target appropriate muscles. Recently, adding external rotation resistance to scapular exercises has gained interest. Moreover, clinical experts advise kinetic chain integration into shoulder rehabilitation exercises. OBJECTIVE: To investigate scapular muscle activity during kinetic chain variations of a prone elevation exercise. METHODS: Activity of the upper (UT), middle (MT), and lower (LT) trapezius and serratus anterior (SA) muscles was determined with surface electromyography (EMG) in 31 asymptomatic participants during six prone elevation exercise variations. Variation was created by adding external rotation resistance, adding trunk extension, or changing exercise position (prone on a Swiss ball with knees or feet supported, or prone on a physiotable). All data were normalized as a percentage of maximal voluntary isometric contraction (% MVIC). For each muscle, a Friedman's ANOVA was conducted to analyse statistical differences in EMG signal intensity between exercises. RESULTS: The LT was moderately (42 - 48% MVIC) and MT highly (63 - 66% MVIC) activated during all exercise variations. No significant differences between exercises for these muscles could be detected. Adding external rotation to a prone elevation exercise decreased UT activity while adding trunk extension increased UT activity. Altering exercise position had no influence on scapular muscle activity except increased UT activity when lying prone on a physiotable with trunk extension. CONCLUSION: Prone elevation exercises are appropriate for facilitating LT and MT activity. Adding external rotation inhibits UT activity while UT facilitation could be achieved when adding trunk extension.

Activation of upper limb muscles in subjects with scapular dyskinesis during bench-press and dumbbell fly on stable and unstable surfaces.

BACKGROUND: Scapular dyskinesis has been associated with shoulder dysfunctions, and changes in electromyographic (EMG) activity have been reported during the execution of some exercises. OBJECTIVE: To compare upper limb muscles EMG of asymptomatic subjects with and without scapular dyskinesis during bench-press and dumbbell fly exercise performed on different surface stability conditions. METHODS: Twenty-eight physically active men were allocated into two groups: Control group (n= 14) and Dyskinesis group (n= 14). The participants performed six repetitions lasting three seconds of the bench press and dumbbell fly exercises with 50% of one-repetition maximum (1RM) on a bench and a Swiss ball. The EMG activity of the pectoralis major, serratus anterior, upper and lower trapezius, anterior deltoid, biceps and triceps muscles were recorded. RESULTS: No differences were found between groups, regardless of exercise or surface type. Inserting the unstable surface in the supine exercise promoted a slight increase in upper trapezius EMG activity for the control [4.32 (95% CI: 1.04 to 7.60)] and dyskinesis [3.30 (95% CI: 0.34 to 6.27)] groups. CONCLUSIONS: There is no difference in upper limb muscle EMG activity between subjects with and without scapular dyskinesis. In addition, inserting unstable surfaces did not modify EMG activity.

Comparing exercises with and without electromyographic biofeedback in subacromial pain syndrome: A randomized controlled trial.

BACKGROUND: Deficits in movement and muscle activation of scapulohumeral joint are related to Subacromial Pain Syndrome. Electromyography biofeedback during exercise may enhance muscle activation and coordination, and consequently improve pain and shoulder function. METHODS: This study compared the effects of an exercise protocol with and without using electromyographic biofeedback on pain, function and movement of the shoulder complex in subjects with Subacromial Pain Syndrome. A total of 24 patients with subacromial pain (mean age = 46.2 + 8.1;18 women) were randomized to either therapeutic exercise or exercise plus biofeedback to the trapezius and serratus muscles. Pain and shoulder function were evaluated as the primary outcome and range of motion, muscle strength, electromyographic activity and scapulohumeral kinematics as secondary outcomes. The subjects underwent eight weeks of intervention and comparisons were made between groups in baseline, at 4 weeks, 8 weeks, and at 4 weeks post intervention. FINDINGS: There were differences between groups for pain [mean difference = 1.5 (CI 0.3, 3.2) p = 0.01] at 8 weeks in the Exercise group and scapular upward rotation at 60° of arm elevation [mean difference = 13.9 (CI 0.9, 9.3), p = 0.006] in the Biofeedback group. There was no difference for the other variables of scapular kinematics as well as for shoulder function (DASH), muscle strength, range of motion and electromyographic variables. INTERPRETATION: The addition of Biofeedback to the exercise protocol increased upward rotation of the scapula. However, the volunteers who performed only the Exercises had a better response in reducing pain.

Correlation between upper limb function and clinical measures of shoulder and trunk mobility and strength in overhead athletes with shoulder pain.

OBJECTIVE: To investigate the correlation between functional performance and self-reported upper limb function and between these two functional measures and clinical measures of shoulder and trunk in overhead athletes with shoulder pain. DESIGN: Cross-sectional study. SETTINGS: Laboratory. PARTICIPANTS: Twenty-one volleyball and handball athletes (23.6 ± 3.7 years) with shoulder pain in the dominant limb. MAIN OUTCOME MEASURES: Self-reported dominant upper limb function using Penn Shoulder Score and Disabilities of the Arm, Shoulder, and Hand; shoulder and trunk range of motion; isometric strength of shoulder, periscapular, and trunk muscles; endurance time of trunk muscles; and functional upper limb performance using the Upper Quarter Y-Balance Test (UQYBT). RESULTS: A moderate correlation was observed (r = 0.45-0.58; p < 0.05) between UQYBT performance and strength of serratus anterior, lower trapezius, trunk rotators, and trunk flexors. No significant correlation was observed between UQYBT performance and the other clinical measures of shoulder and trunk (r = 0.01-0.39, p > 0.05). Self-reported upper limb function was neither significantly correlated with clinical measures (r = 0.01-0.40, p > 0.05) nor with UQYBT performance (r = 0.02-0.19, p > 0.05). CONCLUSION: We observed a correlation between UQYBT performance and strength of periscapular and trunk muscles.

The effects of lifting straps in maximum strength, number of repetitions and muscle activation during lat pull-down.

The objective of the study was to investigate the effects of using lifting straps on the lat pull-down exercise on maximal strength, number of repetitions, and muscle activation. Twelve resistance-trained men participated (age 27 ± 4 years, body mass 84 ± 10 kg, height 177 ± 6 cm, resistance training experience 6.6 ± 2.4 years). All participants performed the 1RM tests and training protocols either with the lifting straps (WS) or without (WOS). Exercise sessions for both conditions (WS and WOS) consisted of 3 sets to concentric failure with a load of 70% of one repetition maximum (1RM) and rest intervals of 60 s. For the 1RM test, no difference was observed between WS and WOS conditions (96.5 ± 12.7 kg and 96.6 ± 11.9 kg, respectively). There were no differences between the WS and WOS conditions in the number of repetitions per set, total repetitions and latissimus dorsi muscle activation. In conclusion, the findings of this study demonstrate that the use of lifting straps in the lat pull-down exercise by resistance-trained individuals does not promote beneficial effect in the 1RM value, the number of repetitions performed with 70% of 1RM, and muscle activation.

Scapular movement training versus standardized exercises for individuals with chronic shoulder pain: protocol for a randomized controlled trial.

BACKGROUND: Scapular focused exercise interventions are frequently used to treat individuals with shoulder pain. However, evidence for changes in scapular motion after intervention is limited. OBJECTIVE: To compare the effects of scapular movement training versus standardized exercises for individuals with shoulder pain. METHODS: This will be a single-blinded randomized controlled trial. Sixty-four individuals with shoulder pain for at least 3 months, scapular dyskinesis, and a positive scapular assistance test will be randomly allocated to one of two groups: Scapular Movement Training (group 1) and Standardized Exercises (group 2). Group 1 will receive education about scapular position and movement, and be trained to modify the scapular movement pattern. Group 2 will perform stretching and strengthening exercises. Both groups will be treated twice a week for eight weeks. Three-dimensional scapular kinematics and muscle activity of the serratus anterior and upper, middle, and lower trapezius during elevation and lowering of the arm will be assessed at baseline and after 8 weeks of treatment. Pain intensity, function, fear avoidance beliefs, and kinesiophobia will be assessed at baseline and after 4 and 8 weeks of treatment, and 4 weeks after the end of treatment. CONCLUSIONS: The results of this study may contribute to a better understanding of the efficacy of scapular focused treatments for individuals with shoulder pain. CLINICAL TRIAL REGISTRATION: NCT03528499.

Optimal activation ratio of the scapular muscles in closed kinetic chain shoulder exercises: A systematic review.

BACKGROUND: Muscle synergies contribute to scapular position during arm movement. The trapezius and serratus anterior (SA) muscles are the main stabilizers and are therefore the main target muscles of therapeutic exercises. OBJECTIVE: To systematically review the current literature investigating the optimal activation ratio of the scapular muscles during a range of closed kinetic chain exercises. METHODS: A systematic review search was conducted to identify studies reporting shoulder electromyography (EMG) activity during rehabilitation exercises in healthy participants. The search was conducted in PubMed, Cochrane Library, MEDLINE, CINAHL, Scopus, SPORTDiscus, and ScienceDirect. The included studies reported closed kinetic chain exercises and the muscle activity as a percentage of maximum voluntary isometric contraction (%MVIC) or muscle ratios of the lower trapezius (LT), middle trapezius (MT), and SA with respect to the upper trapezius (UT). Muscle ratios were classified as optimal if they were equal to or lower than 0.6, and the adapted Newcastle-Ottawa Scale (NOS) was used to evaluate the methodological quality of the selected studies. RESULTS: Twenty-nine studies were included in this review; 7 main exercises and 30 variations of these were reported. The average electromyographic activity of the concentric and eccentric phase was considered. Half Push Up, Push Up Plus, and Scap Protraction exercises showed optimal SA activity (UT/SA < 0.6), while Press Up, Half Push Up, and One Hand Plank exercises showed optimal LT activity (UT/LT < 0.6). According to the NOS, 15 studies were classified as moderate methodological quality. CONCLUSIONS: The exercises in higher positions (e.g. exercises with the trunk closest to the vertical line) or unstable surfaces tend to favor UT activity over the MT, LT and SA. The exercises including scapular retraction showed optimal UT/MT and UT/LT ratios, while those including scapular protraction showed optimal UT/SA ratios. This will assist therapists in the correct selection of exercises for shoulder rehabilitation.

Does sEMG normalization change results on sex differences in the activation of the shoulder girdle muscles during a simulated work task?

The aim was to investigate if the method of normalizing surface electromyography (sEMG) can change results on sex differences in the muscular activation of the shoulder girdle muscles during a simulated work task. sEMG was recorded in 36 asymptomatic participants (17 females, 19 males) from four parts of trapezius and from serratus anterior muscles during a simulated work task. Four normalization methods, one involving maximal voluntary contractions (MVCs) and three involving submaximal voluntary contractions were applied. Sex differences in absolute and normalized amplitude of sEMG were analyzed. The normalization method had a significant influence on the observed sex differences. Females only showed higher sEMG amplitude than males when the sEMGs were normalized to MVC and to a submaximal contraction based on 20% of MVC for the upper trapezius (acromial fibers). Researchers and practitioners should be aware of the impact of the sEMG normalization method in sex differences investigation.

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

BACKGROUND: Modifications 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. OBJECTIVE: To 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. METHODS: Thirty-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. RESULTS: Paired 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). CONCLUSION: The 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.

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

BACKGROUND: The 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. METHODS: This 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. CONCLUSIONS: This 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.

BACKGROUND: The 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. METHODS: This 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. CONCLUSIONS: This 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.

Are there sex differences in muscle coordination of the upper girdle during a sustained motor task?

PURPOSE: The higher prevalence of work-related musculoskeletal disorders among women compared with men could be explained by sex-gender differences related to biological and physiological processes. The aim of this study was to evaluate sex differences in motor coordination during a sustained and repetitive motor task. METHODS: Seventeen healthy females and 21 healthy males participated. The surface electromyography (sEMG) of the trapezius portions and serratus anterior were recorded. Root mean square (RMS) values were computed to assess the level of muscle activity. The standard deviation (SD) and coefficient of variation (CV) were computed as metrics of size of variability. The normalized mutual information (NMI) values were calculated as index of functional connectivity between muscles pairs. RESULTS: Females had higher normalized RMS values for the upper trapezius (acromial fibers) and serratus anterior muscles compared with males. RMS decreased, SD and CV increased while NMI decreased for almost all muscle pairs over time. CONCLUSION: The present work showed some signs of sex differences in muscle coordination of the shoulder girdle during a sustained motor task, performed with the upper limb positioned below of the shoulder level.

Effects of work surface and task difficulty on neck-shoulder posture and trapezius activity during a simulated mouse task.

OBJECTIVES: The purpose of this study is to evaluate the influence of the work surface and task difficulty on the head, upper back and upper arm postures and activity of the descending trapezius during a simulated mouse task. METHODS: Healthy female university students (N = 15) were evaluated. The work surface was positioned at elbow height (EH) and above elbow height (AEH) and the task difficulty was set at low (LD) and high (HD) levels. The postures were recorded by inclinometers. Trapezius activity was normalized by the maximum voluntary isometric contraction (MVIC). RESULTS: Significantly higher head flexion was found at EH compared to the AEH condition, with an average difference of 2°-5° at the same difficulty level. The HD task significantly increased head (3°-6°) and upper back flexion (6°-7°) at the same table height. For upper arm elevation and trapezius activation, the AEH condition presented higher upper arm elevation (about 6°-8°) and trapezius activity (0.8-1.4% of MVIC), regardless of the difficulty level of the task. CONCLUSIONS: Head posture was influenced by the table height and task difficulty; the upper back posture by high difficulty; and upper arm posture and trapezius activity were only influenced by table height.

Comparison of muscle activity from upper trapezius and wrist extensors between dominant and non-dominant upper limbs during computer-based tasks.

BACKGROUND: Sustained low-level muscle activity occurring during computer-based tasks is associated with the development of WMSDs (work-related musculoskeletal disorders) and this biomechanical exposure may be different between limbs. OBJECTIVE: To compare muscle activity from dominant and non-dominant upper trapezius (UT) and wrist extensors (WE) during computer-based tasks in real work settings. METHODS: Forty-five workers were monitored during two hours while performing their usual administrative tasks. Surface electromyography (sEMG) was recorded from UT and WE muscles in both sides. Rest and general exposure variables were calculated. RESULTS: The 50th percentile demonstrated little muscle activity demand, for both dominant and non-dominant UT and no difference between sides was observed. The dominant WE muscles had lower measures of rest and higher muscle activity when compared with the non-dominant side. CONCLUSIONS: Differences in sEMG between upper limbs were only found in WE muscles, probably due to the use of the mouse. The overall low-level muscle activity suggests a constant activation of the same motor units for the entire data-collection period, which can be considered harmful for musculoskeletal health.

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

BACKGROUND: This 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. METHODS: Forty-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. FINDINGS: No 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. INTERPRETATION: Strength 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.

Normalization of the trapezius sEMG signal - a reliability study on women with and without neck-shoulder pain.

OBJECTIVE: To evaluate within- and between-days reliability of two normalization methods of surface electromyography (sEMG) recordings of the trapezius muscle. METHODS: Nineteen women were allocated into 2 groups (healthy and with neck-shoulder pain). The sEMG was recorded in two sessions with 7 days in between sessions. The four portions of the trapezius muscle (the clavicular and acromial fibers of the upper trapezius, the middle and the lower trapezius) were evaluated during maximal and submaximal isometric voluntary contractions. The within- and between-days reliability of both maximal and submaximal contractions were assessed through Intraclass Correlation Coefficient (ICC(2,1) was used for within-day analyses of both maximal and submaximal contractions, and for between-days analyses of maximal contractions while ICC(2,3) was used for between-days analyses of submaximal contractions), Coefficient of Variation, Standard Error of Measurement, and Bland-Altman analysis. RESULTS: In general, submaximal contractions presented higher within-day reliability, with higher ICC values (e.g., middle trapezius - mean of 0.97), smaller Coefficient of Variation and Standard Error of Measurement ranges compared to maximal contractions (ICC values, e.g. for middle trapezius - mean of 0.94) in both groups. The same pattern was observed for between-days analyses, with submaximal contractions presenting higher ICC values (e.g., middle trapezius - mean of 0.84), smaller Coefficient of Variation and Standard Error of Measurement ranges than maximal contractions (ICC values, e.g. for middle trapezius - mean of 0.73) in both groups. CONCLUSION: Submaximal contractions are recommended for normalization procedures of trapezius sEMG, in both subjects with neck-shoulder pain and healthy individuals.

Unilateral and Immediate Stimulation of Acupuncture Points Xiaohai (SI8) and Jianwaishu (SI14) of the Small Intestine Meridian Increases Electromyographic Activity and Strength in the Ipsilateral and Contralateral Upper Trapezius Muscle.

We previously showed that a yin meridian of the upper limb decreased electromyographic activity (root mean square) and muscle strength ipsilateral and contralateral to the side of stimulation. Here, we tested the upper trapezius (UT) muscle response after stimulation of a yang meridian of the upper limb, the small intestine (SI). Thirty-eight healthy volunteers were randomized into the following groups: UT muscle (SI14), distant of the UT muscle (SI8), without stimulation (CG), and sham (R3). An acupuncturist certificated by the Brazilian Society of Physical Therapists and Acupuncturists performed the needle insertion. Each volunteer received only one stimulation to the right upper limb. The evaluation occurred before, 5 minutes after, and 20 minutes after needle withdrawal. The root mean square activity increased on the right side in the UT muscle for the SI8 and SI14 groups (F3,37 = 4.67; p < 0.025) at the 20-minute evaluation. The most vigorous response occurred on the contralateral side because the effects were maintained for 5 minutes after withdrawal (F3,37 = 4.52; p < 0.025). Both groups showed an increase in the UT muscle strength at the 20-minute evaluation (F3,37 = 3.41; p < 0.025). The CG and R3 groups did not show any changes. Our data indicate that SI a yang meridian increases the UT muscle response.