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.

Reliability of the Joint Position Sense Error Test for Women With Neck Pain and Asymptomatic Men and Women.

OBJECTIVE: The purpose of this study was to evaluate the intra-rater between-days reliability of the joint position sense error (JPSE) test in asymptomatic men and women, as well as in women with neck pain. METHODS: Fourteen asymptomatic men and 27 women (14 asymptomatic and 13 with neck pain) participated. The JPSE test was performed during right and left cervical rotation (10 trials for each side) in 2 sessions, with at least 7 days between them. The head repositioning error during the JPSE test (in degrees) was measured and used to calculate the intra-rater between-days reliability of the test, evaluated through the intraclass correlation coefficient and Bland-Altman analyses. Independent t tests were calculated to compare the head repositioning errors of asymptomatic women and men. The minimal detectable change was also calculated. RESULTS: The neck pain group showed higher intraclass correlation coefficient values (0.866 and 0.773, good reliability) compared to the asymptomatic men (0.478 and 0.403, poor reliability) and to the asymptomatic women (-0.161 and 0.504, poor and moderate reliability, respectively) for both right and left cervical rotation, respectively. Considering Bland-Altman analyses, the neck pain group showed better agreement between the measurements for right cervical rotation than the asymptomatic groups. CONCLUSION: The results indicate that the methodology used to perform the JPSE test in this study may be a reliable way to assess the proprioception of women with neck pain in clinical settings.

Serratus anterior sEMG - sensor placement and test position for normalization purposes during maximal and submaximal exertions.

There is great variability regarding serratus anterior sEMG sensor placement and test positions during normalization procedures. We investigated between-trials reliability of serratus anterior sEMG, acquired at two sensor placements and four test positions, during maximal and submaximal isometric contractions. Twenty young healthy women participated. sEMG was captured at the 7th intercostal space and at the xiphoid process level, in the mid-axillary line, during maximal and submaximal isometric contractions, in four test positions. Intraclass Correlation Coefficient (ICC2,1), coefficient of variation and standard error of measurement were calculated. Interactions between sensor placements and test positions were investigated using a two-way repeated-measures ANOVA. All test conditions presented ICC2,1 > 0.8. There was no interaction between sensor placement and test position. Signal obtained from the sensor at 7th intercostal space was more stable between-trials and showed higher amplitude, during maximal and submaximal contractions, at seated positions with shoulder protracted at both 90° or 125° of flexion. We suggest to acquire serratus anterior sEMG at the 7th intercostal space and perform maximal or submaximal isometric contractions for signal normalization with shoulder protracted and flexed, at seated position.

Sex differences in postures of the upper body during a simulated work task performed above shoulder level.

The aim of this study was to evaluate if there are sex differences in postures of upper arm, upper back, head and neck after muscle fatigue induced by a simulated work task, requiring upper arm movements performed above shoulder level. Nineteen females and 18 males were evaluated. Upper arm elevation, upper back, head and neck forward flexion postures were recorded using digital inclinometers. The first and the last cycles of the task were considered as pre- and post-fatigue periods, respectively. For both periods, Amplitude Probability Distribution Function (APDF) was calculated for 10th, 50th and 90th percentiles, as well as the angular ranges between the 5th and 95th percentiles (APDF5-95 range). The APDF5-95 range for upper arm elevation was higher with fatigue, but with a higher increase for males. After fatigue, there was also a decrease in the upper arm elevation, with a larger decrease in males for the 10th and 50th percentiles. For head and neck, females showed higher APDF5-95 ranges than males, regardless of the task period evaluated. After muscle fatigue, males adopted more neutral postures of the upper arm than females. Furthermore, females showed more non-neutral postures for head and neck. These findings suggest that the kinematic strategies adopted by females and males during a simulated work task are different and may predispose females to a higher risk of developing work-related musculoskeletal disorders of the neck.

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.

Acute Effects of the 6-Minute Pegboard and Ring Test in COPD.

BACKGROUND: There are few reports in the literature supporting the understanding of the physiological mechanisms of intolerance in patients with COPD to perform unsupported upper limb activities. The aims of this study were to quantify the electrical activity and oxygenation of inspiratory and upper limb muscles, and to investigate whether electromyographic manifestations of muscle fatigue are related to upper limb function as assessed by the 6-min pegboard and ring test (6PBRT) in subjects with COPD and in healthy subjects. METHODS: Thirty subjects with COPD (FEV1 42.1 ± 16.4% predicted; 68.0 ± 7.6 y old) comprised the COPD group, and 34 healthy subjects (66.8 ± 8.0 y old) comprised the control group. Both groups were assessed for body composition with dual-energy radiograph absorptiometry and spirometry. The 6PBRT was performed with simultaneous assessment of electromyography, near-infrared spectroscopy, and gas analyses (expiratory minute volume). RESULTS: Differences were observed between groups for performance (number of rings) in the 6PBRT, with the COPD group achieving lower values than the control group (P < .001). The ventilatory demand (expiratory minute volume/maximum voluntary ventilation) and root mean square amplitude of the sternocleidomastoid muscle were higher in the COPD group than in the control group (P < .04). Lower values for oxyhemoglobin and total hemoglobin were found in intercostal muscles of the COPD group compared to the control group. The root mean square amplitude of the intercostal muscles was lower in the COPD group, while it was similar between groups for anterior deltoid and trapezius muscles. Median frequency of anterior deltoid muscles presented a decreased in both groups. CONCLUSIONS: Our results indicate that the 6PBRT was performed at a higher electrical activity in the accessory inspiratory muscles, such as the sternocleidomastoid muscle, and a lower oxygenation profile in the intercostal muscles in subjects with COPD compared with healthy controls, but without muscle fatigue signs. These findings suggest that the higher ventilatory demand presented in subjects with COPD could have contributed to the worse performance in this group without signals of peripheral muscle limitation.

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.

Can exposure variation be promoted in the shoulder girdle muscles by modifying work pace and inserting pauses during simulated assembly work?

This study investigated the acute effects of changing the work pace and implementing two pause types during an assembly task. Eighteen healthy women performed a simulated task in four different conditions: 1) slow or 2) fast work pace with 3) passive or 4) active pauses every two minutes. The root mean square (RMS) and exposure variation analysis (EVA) from the trapezius and serratus anterior muscles, as well as the rate of perceived exertion (RPE) from the neck-shoulder region, were observed. Decreased RMS and RPE as well as more variable muscle activity (EVA) were observed in the slow work pace compared with the fast one. The pause types had a limited effect, but active pauses resulted in increased RMS of the clavicular trapezius. The findings revealed the importance of work pace in the reduction of perceived exertion and promotion of variation in muscle activation during assembly tasks. However, the pause types had no important effect on the evaluated outcomes.

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.

The coordination of shoulder girdle muscles during repetitive arm movements at either slow or fast pace among women with or without neck-shoulder pain.

PURPOSE: The aim of this study was to evaluate the coordination of the shoulder girdle muscles among subjects with or without neck-shoulder pain performing repetitive arm movement at either a slow or fast pace. METHODS: Thirty female adults were allocated to one of two groups-healthy controls or cases with neck-shoulder pain. Surface electromyography (sEMG) signals from the clavicular, acromial, middle and lower trapezius portions and the serratus anterior muscles were recorded during a task performed for 20min at a slow pace and 20min at a fast pace. The root mean square (RMS), relative rest time (RRT) and normalised mutual information (NMI, an index of functional connectivity between two muscles in a pair) were computed. RESULTS: No significant differences on RMS, RRT and NMI were found between groups. For both groups, the fast movement pace resulted in increased levels of RMS, lower degrees of RRT and higher NMI compared to the slow pace. No interaction between group and movement pace was found. CONCLUSIONS: This study highlights the change in sEMG activity of muscles to meet the demands of performing a task at fast movement pace. The fast pace imposed a higher muscle demand evidenced by increased sEMG amplitude, low degree of muscle rest and increased functional connectivity for subjects in both the case and control groups. No indication of impaired sEMG activity was found in individuals with neck-shoulder pain.

Effects of active pause pattern of surface electromyographic activity among subjects performing monotonous tasks: A systematic review.

Active pauses have shown potentially beneficial effects to increase the variability of the electrical activation pattern of muscles. However, there is a lack of consensus as to how to design and implement those pauses and the processing methods of surface electromyography (EMG) data when evaluating low-level monotonous tasks. The aim of this systematic review was to synthesize the evidences regarding the way which active pauses have been applied, and the methods used to investigate the related EMG changes. PubMed-MEDLINE, Embase, Web of Science, Lilacs, Ebsco, and Scopus databases were searched. Two authors independently extracted data from the primary studies. The methodological quality was assessed using a list from van der Windt et al. (2000), and the level of evidence was synthesized through GRADE. The ISEK guideline for reporting EMG data was also applied as a checklist. Fifteen studies were included - 14 with high methodological quality. In general, active pauses were able to change the level of EMG activity in monotonous tasks. The level of evidence through GRADE was very low for all EMG processing methods, except RMS which was low. A vast heterogeneity concerning the methods applied to analyze EMG data contributed to decrease the quality of evidence synthesis, and the findings need to be carefully considered. The GRADE approach and the ISEK guideline contributed to identify important flaws in the literature. Future studies investigating active pauses in longitudinal studies and following the standard for recording and reporting EMG data care are warranted.