Shoulder Muscle Activity Research Articles

An investigation into four different sit–stand workstation use schedules

Twelve office workers participated in a study investigating effects of four sit/stand schedules (90-min sit/30-min stand, 80/40, 105/15, and 60/60) via several objective and subjective measures (muscle fatigue, foot swelling, spinal shrinkage, and self-reported discomfort). Results showed that there were no significant differences in shoulder and low back static muscle activities between sitting and standing. Muscle fatigue was developed during workday under all schedules. The longest standing schedule seemed to have a tendency of reducing muscle fatigue. None of the schedules helped or worsened foot swelling and spinal shrinkage. More active break-time activities seemed reducing muscle fatigue and foot swelling. While the self-reported bodily discomfort levels were generally low, the preferred schedules among the participants were varied, although the least standing schedule was the least preferred. We may conclude that effects of using sit–stand workstation to improve musculoskeletal health may be limited but promoting more active break-time activities can help.Practitioner Summary: Sit–stand workstations are used to reduce work-related musculoskeletal disorders. This study shows that office workers prefer sit/stand durations in the range between 1:1 and 3:1. Longer standing may have the potential to reduce muscle fatigue. However, active break-time activities may be more effective in reducing muscle fatigue and foot swelling.

Shoulder muscles activity can be non-invasively evaluated using ultrasonography shear wave elastography

Shoulder muscles activity can be non-invasively evaluated using ultrasonography shear wave elastography

Adaptive Control of a Neuroprosthesis for Stroke Patients Amplifying Weak Residual Shoulder-Muscle Activity

Stroke patients often suffer from a partial paralysis hindering shoulder elevation movements. To support the small voluntary forces, Functional Electrical Stimulation (FES) can be applied to the shoulder-deltoid muscle for gaining additional force. In previous research we presented a positive-feedback control loop which applies a stimulation level that causes the arm abduction to be hold at a given percentage (support factor) of the currently measured angle. This approach causes an amplification of the effect of the residual volitional activity and effectively realizes an arm weight relief. The support-level strongly influences the closed-loop’s behavior especially for percentages close to 100% and, therefore, must be carefully chosen to meet the patient’s requirements. Because of parameter variations, this value cannot be precisely pre-computed, and, hence, we present an adaptive trial-to-trial based learning procedure to iteratively realize a given level of volitional amplification. During each trial, the algorithm obtains measurements of the volitional activity obtained by means of Electromyography (EMG) and the joint angle. After the arm returns to its rest position, the achieved amplification of the volitional activity is estimated. An integral controller combined with a non-linear output transformation then updates the support factor for the next trial aiming to realize the desired volitional amplification. The closed-loop adaptive controller is robust asymptotically stable. In two tests performed on a healthy subject, the desired level of volitional amplification was reached within 3 to 5 trials demonstrating the feasibility of the chosen approach.

The Onset Time of Neck and Shoulder Muscles Activation During Shoulder Elevation in Older and Young Adults

This study examined differences in the time to onset of neck and shoulder muscle activation during arm elevation in older and younger adults. Eleven older and 10 younger adults were recruited. Data from neck and shoulder muscles were recorded as a subject elevated one arm. The mean time to onset of muscle activation was compared using an independent t-test. Older adults demonstrated significantly later onset of contraction of the ipsilateral sternocleidomastoid during shoulder flexion (p = 0.046), as well as significantly later contraction of the middle deltoid (p = 0.005), posterior deltoid (p = 0.027), contralateral splenius capitis (p = 0.008), upper trapezius (p = 0.020), middle trapezius (p = 0.012), lower trapezius (p = 0.012), and infraspinatus (p = 0.001) during shoulder abduction. These findings indicate that older adults use different neuromuscular strategies than younger adults during arm elevation. These changes could result from age-related decline in the neuromuscular system. The findings could be used to identify contributors to neck and shoulder discomfort or dysfunctionin older adults.

Shoulder Muscle Activity in Sport Climbing in Naturally Chosen and Corrected Shoulder Positions

Objective:The aim of the study was to determine electromyographic activity of the scapula stabilizing muscles in naturally chosen and corrected shoulder positions in typical static climbing postures.Methods:Six male participants undertook surface electromyography measurement in four climbing postures for two different shoulder positions. The activity of the lower, middle and upper trapezius, serratus anterior, pectoralis major, and sternocleidomastoid was recorded. Electromyographic activity was expressed as the percentage of maximal voluntary contraction (MVC) for each muscle.Results:Climbing postures induced higher activation of middle and lower trapezius in corrected shoulder positions (35.3 ± 11.8 and 61.7 ± 15.4% MVC respectively) than in naturally chosen shoulder positions (18.4 ± 8.9 and 30.1 ± 13.8% MVC respectively). The highest activity of the middle and lower trapezius was found in postures with the arm in external rotation and 90° abduction and in an overhanging posture. Low activation was stated for the other muscles in both shoulder conditions.Conclusion:Results showed that climbers naturally elevate the shoulder during typical static postures. Corrected shoulder positions induce higher activation of the scapula stabilizing muscles than naturally chosen shoulder positions.

Evaluating biomechanics of user-selected sitting and standing computer workstation

A standing computer workstation has now become a popular modern work place intervention to reduce sedentary behavior at work. However, user's interaction related to a standing computer workstation and its differences with a sitting workstation need to be understood to assist in developing recommendations for use and set up. The study compared the differences in upper extremity posture and muscle activity between user-selected sitting and standing workstation setups. Twenty participants (10 females, 10 males) volunteered for the study. 3-D posture, surface electromyography, and user-reported discomfort were measured while completing simulated tasks with each participant's self-selected workstation setups. Sitting computer workstation associated with more non-neutral shoulder postures and greater shoulder muscle activity, while standing computer workstation induced greater wrist adduction angle and greater extensor carpi radialis muscle activity. Sitting computer workstation also associated with greater shoulder abduction postural variation (90th–10th percentile) while standing computer workstation associated with greater variation for should rotation and wrist extension. Users reported similar overall discomfort levels within the first 10 min of work but had more than twice as much discomfort while standing than sitting after 45 min; with most discomfort reported in the low back for standing and shoulder for sitting. These different measures provide understanding in users' different interactions with sitting and standing and by alternating between the two configurations in short bouts may be a way of changing the loading pattern on the upper extremity.

Differences between clinician- and self-administered shoulder sustained mobilization on scapular and shoulder muscle activity during shoulder abduction: A repeated-measures study on asymptomatic individuals

BackgroundSustained glenohumeral postero-lateral glide administered by a clinician is commonly used in the management of patients with shoulder pain. This technique reduced shoulder muscle activity in asymptomatic individuals, but it is unknown whether a self-administered version of the mobilization leads to similar neuromuscular response. This study compared the effect of sustained shoulder mobilizations (performed by a physiotherapist) with self-administered mobilization (with a belt) on activity levels of scapular and glenohumeral shoulder muscles. MethodsTwenty-two individuals participated in this study, which had a cross-over, repeated measures design. Seven shoulder muscles (upper and lower trapezius, supraspinatus, infraspinatus, posterior deltoid, middle deltoid, and serratus anterior) were monitored using surface electromyography (SEMG) during shoulder abduction performed with a clinician-administered sustained mobilization, and with self-administered sustained mobilization. Muscle activity levels were measured prior, during and after the sustained glide was applied to the shoulder. Mixed-effect models for repeated measures were used for within- and between-condition comparisons. ResultsThere was no carry-over effect. Within-condition comparisons suggest that both interventions lead to changes in scapular and shoulder muscle activity levels. No differences between clinician-administered and self-administered mobilizations at intervention and follow-up were found for the monitored muscles, with the exception of upper trapezius. ConclusionsIn young, asymptomatic individuals, self- or clinician-administered sustained mobilizations reduced activity levels of most scapular and shoulder muscles during shoulder abduction. This effect was observed only while the sustained glides were applied to the shoulder. At the immediate follow-up, muscle activity levels were similar to baseline measurements.

Comparison of the Effects of Different Foot Positions During Body-lifting in Wheelchair on Shoulder Muscle Activities, Peak Plantar Pressure, Knee Flexion Angle, and Rating Perceived Exertion in Individuals With Spinal Cord Injury

Comparison of the Effects of Different Foot Positions During Body-lifting in Wheelchair on Shoulder Muscle Activities, Peak Plantar Pressure, Knee Flexion Angle, and Rating Perceived Exertion in Individuals With Spinal Cord Injury

Influence of Posture Variation on Shoulder Muscle Activity, Heart Rate, and Perceived Exertion in a Repetitive Manual Task

OCCUPATIONAL APPLICATIONS In repetitive work, more physical variation is believed to reduce the risk of eventually developing musculoskeletal disorders. We investigated the extent to which workstation designs leading to more variation in upper arm postures during a pick-and-place task influenced outcomes of relevance to musculoskeletal disorder risk, including muscle activity, cardiovascular response, and perceived exertion, measured through the maximal acceptable work pace. Posture variation to the extent obtained in our experiment had only minor effects on these outcomes, and considerably less impact than a moderate change in working height. Apparently, substantial manipulations of the workstation or of the work task will be needed to accomplish variation to an extent that can significantly change outcomes of relevance to occupational musculoskeletal disorders and, thus, represent a potential for reduction in musculoskeletal disorder risk.TECHNICAL ABSTRACT Background: Repetitive light assembly work is associated with an increased risk for developing work-related musculoskeletal disorders. More exposure variation, for instance by redesigning the workstation, has been proposed as an effective intervention. Purpose: We investigated the effect of upper arm posture variation in a 1-hour repetitive pick-and-place task on shoulder muscle activity, heart rate, and perceived exertion, measured on the Borg CR-10 scale and in terms of maximal acceptable work pace (MAWP). Methods: Thirteen healthy participants performed the task in three workstation designs where the hand was moved either horizontally (H30/30), diagonally (D20/40), or vertically (V10/50), with a mean upper arm elevation of ∼30°. In a fourth design, the hand was moved horizontally at ∼50° mean arm elevation (H50/50). Results: As intended, upper arm posture variation, measured by the upper arm elevation standard deviation and range of motion, differed between H30/30, D20/40, and V10/50. However, MAWP (10.7 cycles·min−1 on average across conditions; determined using a psychophysical approach), mean upper trapezius activity (54% reference voluntary exertion [RVE]), and heart rate (69 bpm) did not differ between these workstation designs. In H50/50, MAWP was lower (9.3 cycles·min−1), while trapezius activity (78% RVE) and perceived exertion (Borg CR-10) tended to be higher. Conclusions: Our results indicate that posture variation to the extent achieved in the current experiment leads to less effects on muscle activity and perceived exertion than a moderate change in working height.

The effects of electromyography-triggered electrical stimulation on shoulder subluxation, muscle activation, pain, and function in persons with stroke: A pilot study.

The purpose of this study was to examine the effects of task-oriented electromyography-triggered stimulation for shoulder subluxation, muscle activation, pain and upper extremity function in hemiparetic stroke patients. Twenty participants with subacute hemiparetic stroke were recruited for this study and were randomly divided into two groups: experimental group (n = 10) and control group (n = 10). Subjects in the experimental group participated in task-oriented electromyography triggered stimulation for 30 minutes, five times a week for four weeks, whereas the control group received cyclic functional electrical stimulation for 30 minutes, five times a week for four weeks. Subjects in both groups received conventional physical therapy for four weeks (30 min/day, five times/week). Data collected included the degree of shoulder subluxation which had been confirmed by X-ray, muscle activation of the supraspinatus and posterior deltoid muscles by electromyography, pain by the Visual Analogue Scale (VAS), and hand function by the Fugl-Meyer Assessment (FMA) before and after the four week exercise period. The results showed significant improvement in shoulder subluxation, muscle activation, and VAS results in the experimental group, compared with the control group(p < 0.05). FMA scores showed no significant differences between the two groups. In conclusion, task-oriented electromyography-triggered stimulation improved shoulder subluxation, muscle activation, pain and upper extremity function. These results suggest that task-oriented electromyography-triggered stimulation is effective and beneficial for individuals with subacute stroke, and that further studies should be conducted on multivarious anatomical regions.

Grade-IV inferior glenohumeral mobilization does not immediately alter shoulder and scapular muscle activity: a repeated-measures study in asymptomatic individuals

Objectives: To assess: (1) the presence of any carry-over effect between interventions; (2) the immediate effects of inferior shoulder mobilization on shoulder and scapular muscle activity; and (3) to compare muscle activity response between the control and mobilization conditions. Repeated measures, cross-over, pre-post intervention study with sample of convenience.Methods: Twenty-two asymptomatic individuals performed 10 repetitions of shoulder abduction before and after the control and mobilization, with a dosage of three sets of 30-s duration, with grade-IV. The order of intervention was randomized. Surface electromyography was used for recording activity of upper and lower trapezius; anterior, middle and posterior deltoids; supraspinatus; infraspinatus; and serratus anterior. Repeated measures mixed-model analysis of variance was used to assess immediate changes in muscle activity levels following inferior shoulder mobilization. Statistical parametric mapping (SPM) was used for comparing muscle activity waveforms between control and mobilization conditions throughout the range of motion.Results: No systematic changes in muscle activity levels were found between: (1) baseline and follow-up for each condition, at the concentric and eccentric phases of shoulder abduction; (2) control and mobilization conditions during the concentric and eccentric phases of shoulder abduction. SPM results suggested no differences in muscle activity pattern between conditions.Conclusions: Inferior shoulder mobilization did not produce immediate effects on shoulder and scapular muscle activity. It is possible that the dose used was insufficient to generate an immediate neuromuscular response to the mobilization.

Neck and Shoulder Muscle Activation Among Experienced and Inexperienced Pilots in +Gz Exposure.

The aim of the present study was to compare differences in electromyography (EMG) activation of the neck and shoulder muscles between groups of inexperienced and experienced pilots during controlled +Gz exposure in a centrifuge. The subjects were volunteer cadets (inexperienced group) and lieutenants (experienced group) undergoing their first centrifuge training. The first group did not have any high performance aircraft (HPA) experience, while the latter one had a 1-yr experience of intense flying of HPA. During the centrifuge run, EMG activity was recorded from the left and right shoulder, neck flexor, and neck extensor muscles. The pilots without HPA experience had significantly higher muscle activity in the neck flexor and extensor muscles during the last 5 s of the recorded period at G levels exceeding +7.4. Muscle activity in the neck and shoulder muscles was gradually higher among the whole study group with increasing +Gz forces. Because pilots without any HPA experience had significantly higher muscle activity than their counterparts with experience of HPA, we suppose that the experience of high +Gz forces might lead to lower muscle activation in the same flight mission.Honkanen T, Oksa J, Mäntysaari MJ, Kyröläinen H, Avela J. Neck and shoulder muscle activation among experienced and inexperienced pilots in +Gz exposure. Aerosp Med Hum Perform. 2017; 88(2):90-95.

The effects of hand force variation on shoulder muscle activation during submaximal exertions

Upper limb injuries are highly prevalent in the workplace and new tools are needed to proactively design workstations to reduce injury risk. The objective was to characterize spatial, load and direction dependency of muscle activity for hand exertions in the upper limb workspace. Electromyographic signals were collected from 14 upper limb muscles during exertions for all combinations of 4 submaximal hand forces (20/30/50/60 N) in 6 cardinal (up/down/left/right/forward/backward) directions at 5 hand locations. Linear muscle activity increases accompanied increased hand forces. Total muscle activity increases between 20 and 60 N hand forces ranged by direction from 92% (downward) to 189% (right). Prediction equations for all muscles depended on hand force, and linear, quadratic and interaction permutations of hand location. Muscle activity associated with manual tasks is load, direction and spatially dependent. Equations developed to describe these complex relationships can be used to better design future and evaluate current occupational activities.

A comparison of the shoulder and trunk muscle activity according to the various resistance condition during push up plus in four point kneeling.

[Purpose] This study was to compare the shoulder and trunk muscle activity according to the various resistance condition during knee push-up-plus. [Subjects and Methods] Twenty healthy adults participated in this study (9 males and 11 females). The subjects performed dominant-leg-extended knee push-up-plus apply to resistance in the direction of abduction, adduction, extension and the flexion. The surface Electromyography activities of the upper trapezius, serratus anterior, homolateral external oblique and the heterolateral internal oblique were measured. The Electromyography activities of each muscle were compared using a one-way repeated analysis of variance. [Results] The Electromyography activities of serratus anterior and external oblique muscles between the resistance directions were significantly increased extension. The Electromyography activities of heterolateral internal oblique muscle between the resistance directions were significantly increased adduction. [Conclusion] To suggest use of the decision exercise tolerance orientation when muscle strengthening exercises for shoulder and trunk according to variation resistance in lower extremity during Push-up-plus.

The effect of the push-up plus on shoulder muscle activation while using a sling with a pulley.

[Purpose] This study was conducted to investigate the effects of the push-up plus while using a balance ball, a sling, and a sling with a pulley in a creeping position on an unstable floor. [Subjects and Methods] The subjects were divided into three groups of 15 members each who performed the different three type methods of push-up plus (with scapulae protruding) in a random order while in a creeping posture. The muscle activity of each group in the push-up plus posture was measured using electromyography, and the measurement values were compared among the groups using one-way analysis of variance (ANOVA). [Results] The intergroup comparison revealed that the activation of the pectoralis major muscle of the balance ball exercise group was significantly decreased. In this comparison, the activity ratio for the pectoralis major muscles of the balance ball exercise group significantly decreased, and the activity ratio of their serratus anterior muscles significantly increased. From the post analysis, the differences in the activity ratios of the pectoralis major and serratus anterior muscles for the balance ball exercise group were significant when compared with those of the other groups. [Conclusion] Among the three different exercise methods in unstable situations presented in this study, the push-up plus exercise in a creeping posture using the balance ball can be recommended for the selective strengthening of the serratus anterior muscle.

Optimized maximum voluntary exertion protocol for normalizing shoulder muscle activity

Muscle activity is typically normalized to maximal activation from isometric maximum voluntary exertions (MVE) in posture and direction specific exertions for each muscle. This is challenging for the shoulder complex due to the large number of muscles. The objective of this investigation was to compare maximum shoulder muscle activity elicited from a multi-muscle MVE test protocol versus individual muscle MVE tests and determine their reliability. Ten healthy males had muscle activity recorded from 12 trunk and upper extremity muscles while performing 3 repetitions of 12 individual and 4 multi-muscle MVEs. Peak surface EMG (sEMG) amplitudes were compared using paired sample t-tests between the two protocols for each muscle. Individual muscle test maximum sEMG amplitudes differed significantly from the multi-muscle test protocol in 3 of 12 muscles (p < 0.05). In muscles that did not attain statistical significance, maximum amplitude differences of 6–15% were found. There was high reliability (Interclass Correlation Coefficient, ICC = 0.831–0.986) and no significant differences between the second and third repetitions of the protocol. Since differences of 6–15% could have functional significance, 8 MVE tests (3 multi-muscle, 5 individual muscle) were selected for future use. Using two repetitions of the reduced MVE protocol will reduce time, risk of pain and injury during experiments.

The effect of visual field condition on kinetic in upper extremities and e.m.g in lower extremities while performing reaching in normal adults.

[Purpose] The aims of this study was to investigate mean velocity and angle of shoulder joint, activation of tibialis anterior and gastrocnemius according to both eyes, dominant eye and non-dominant eye condition during reaching task in normal adults. [Subjects and Methods] Our research recruited 24 participants (male 11, female 13) in Silla University. Participants were performed reaching out movement by conditions of both eye, dominants eye, non-dominants eye. The target was placed at 45 degree diagonal direction and distance far away 130% of their arm length. Kinetic analysis of the upper extremities was investigated by QUALISYS 3-dimensional motion analysis system. Muscle activation were measured by EMG during reaching tasks. The collected data were statistically processed using the SPSS for win version 20.0. [Results] There was a significant difference of shoulder joint velocity of flexion, abduction and internal rotation according to visual field condition during reaching tasks. There was no significant difference of shoulder joint angle and muscle activation according to visual field conditions during reaching tasks. [Conclusion] In conclusion, visual field has an influence on shoulder joint velocity. Therefore, the visual field may be to play an important role in reach performance.

The comparisons of tape of different type applied on forward head posture positions

Objectives: This study is to find out the effect on the neck and shoulder muscle activation changes when applying the elastic and non-elastic tape in forward head posture. Methods/Statistical Analysis: After preliminary research, 30 adult males and females were recruited and agreed to participate as the subject in this study. All subjects were measured their muscle activation with forward head posture, attaching the elastic tape, non-elastic tape and not attaching the tape by using Electromyography (EMG) equipment. The muscle activation of upper trapezius and splenius capitis is analyzed by using a one-way repeated ANOVA. Findings: As a result of the measurement value comparisons, applying non-elastic tape statically decrease muscle activation than elastic tape in the forward head posture (p<.05). Improvements/Applications: The result shows that non-elastic tape is more useful for forward head posture to support.

Upper Extremity and Cue Kinematics, and Shoulder Muscle Electromyographic Activity of Novus Players of Different Skill Levels.

Our aim with the current study was to compare upper extremity and cue kinematics, and electromyographic (EMG) activation of shoulder muscles during novus (a special form of billiards) shots of different difficulty levels. Ten proficient and 10 less-skilled novus players performed 3 types of novus shots (penalties, cuts, rebounds) 10 times each. During each shot, elbow flexion and cue-forearm angles (using a movement analysis system), and surface EMG activity of the trapezius, posterior, and lateral deltoid muscles of each subject's dominant side, were measured. Data were compared between more- and less-skilled players, and successful compared with unsuccessful shots. Elbow flexion angle among the more-skilled players was 24.5% larger (P < .001) during unsuccessful cut shots than successful ones. The more-skilled players performed successful penalty and rebound shots with 26.8% and 49.8% lower (P < .01 and P < .001, respectively) EMG activity of the trapezius muscle than unsuccessful ones. Less-skilled players' shots were characterized by higher EMG activity in the trapezius muscle. The obtained findings suggest that the more-skilled novus players had acquired a different muscle recruitment pattern than less-skilled players.

Shoulder Muscle Activation Levels During the Push-Up-Plus Exercise on Stable and Unstable Surfaces.

The aim of this study was to evaluate the acute effect of the use of stable and unstable surfaces on electromyography (EMG) activity and coactivation of the scapular and upper-limb muscles during the push-up plus (with full protraction of the scapula). Muscle activation of anterior deltoid (AD), posterior deltoid (PD), pectoralis major, biceps brachii (BB), triceps brachii (TB), upper trapezius (UT), middle trapezius (MT), lower trapezius (LT), and serratus anterior (SA) levels and coactivation index were determined by surface EMG in 20 young men during push-up plus performed on a stable and unstable condition (2 unstable devices applied to hands and feet). The paired t test and Cohen d were used for statistical analysis. The results showed that during the execution of the push-up plus on the unstable surface an increased EMG activity of the scapular stabilizing muscles (SA, MT, and LT) was observed, while AD and PD muscles showed a decrease. During exercise execution on the unstable surface there was a higher index of coactivation of the scapular muscles (SA-MT and UT-LT pairs). No significant differences were observed in TB-BB and AD-PD pairs. These results suggest that the push-up-plus exercise associated with unstable surfaces produced greater EMG activity levels and coactivation index of the scapular stabilizing muscle. On the other hand, the use of an unstable surface does not promote the same effect for the shoulder muscles.