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David C. Ackland - One of the best experts on this subject based on the ideXlab platform.
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Modulation of Shoulder Muscle and joint function using a powered upper-limb exoskeleton.
Journal of biomechanics, 2018Co-Authors: Justin Fong, Vincent Crocher, Peter Vee Sin Lee, Denny Oetomo, Ying Tan, David C. AcklandAbstract:Abstract Robotic-assistive exoskeletons can enable frequent repetitive movements without the presence of a full-time therapist; however, human-machine interaction and the capacity of powered exoskeletons to attenuate Shoulder Muscle and joint loading is poorly understood. This study aimed to quantify Shoulder Muscle and joint force during assisted activities of daily living using a powered robotic upper limb exoskeleton (ArmeoPower, Hocoma). Six healthy male subjects performed abduction, flexion, horizontal flexion, reaching and nose touching activities. These tasks were repeated under two conditions: (i) the exoskeleton compensating only for its own weight, and (ii) the exoskeleton providing full upper limb gravity compensation (i.e., weightlessness). Muscle EMG, joint kinematics and joint torques were simultaneously recorded, and Shoulder Muscle and joint forces calculated using personalized musculoskeletal models of each subject’s upper limb. The exoskeleton reduced peak joint torques, Muscle forces and joint loading by up to 74.8% (0.113 Nm/kg), 88.8% (5.8%BW) and 68.4% (75.6%BW), respectively, with the degree of load attenuation strongly task dependent. The peak compressive, anterior and superior glenohumeral joint force during assisted nose touching was 36.4% (24.6%BW), 72.4% (13.1%BW) and 85.0% (17.2%BW) lower than that during unassisted nose touching, respectively. The present study showed that upper limb weight compensation using an assistive exoskeleton may increase glenohumeral joint stability, since deltoid Muscle force, which is the primary contributor to superior glenohumeral joint shear, is attenuated; however, prominent exoskeleton interaction moments are required to position and control the upper limb in space, even under full gravity compensation conditions. The modeling framework and results may be useful in planning targeted upper limb robotic rehabilitation tasks.
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The sensitivity of Shoulder Muscle and joint force predictions to changes in joint kinematics: A Monte-Carlo analysis.
Gait & posture, 2017Co-Authors: Peter Vee Sin Lee, David C. AcklandAbstract:Kinematics of the Shoulder girdle obtained from non-invasive measurement systems such as video motion analysis, accelerometers and magnetic tracking sensors has been shown to be adversely affected by instrumentation measurement errors and skin motion artefact. The degree to which musculoskeletal model calculations of Shoulder Muscle and joint loading are influenced by variations in joint kinematics is currently not well understood. A three-dimensional musculoskeletal model of the upper limb was used to evaluate the sensitivity of Shoulder Muscle and joint force. Monte-Carlo analyses were performed by randomly perturbing scapular and humeral joint coordinates during abduction and flexion. Muscle and joint force calculations were generally most sensitive to changes in the kinematics of the humerus in elevation and of the scapula in medial-lateral rotation, and were least sensitive to changes in humerus plane of elevation and scapula protraction-retraction. Overall model sensitivity was greater during abduction than flexion, and the influence of specific kinematics perturbations varied from Muscle to Muscle. In general, Muscles that generated greater force, such as the middle deltoid and subscapularis, were more sensitive to changes in Shoulder kinematics. This study suggests that musculoskeletal model sensitivity to changes in kinematics is task-specific, and varies depending on the plane of motion. Calculations of Shoulder Muscle and joint function depend on reliable humeral and scapula motion data, particularly that of humeral elevation and scapula medial-lateral rotation. The findings in this study have implications for the use of kinematic data in musculoskeletal model development and simulations.
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subject specific musculoskeletal modeling in the evaluation of Shoulder Muscle and joint function
Journal of Biomechanics, 2016Co-Authors: Peter Vee Sin Lee, Adam L Bryant, Mary P Galea, David C. AcklandAbstract:Upper limb Muscle force estimation using Hill-type Muscle models depends on musculotendon parameter values, which cannot be readily measured non-invasively. Generic and scaled-generic parameters may be quickly and easily employed, but these approaches do not account for an individual subject’s joint torque capacity. The objective of the present study was to develop a subject-specific experimental testing and modeling framework to evaluate Shoulder Muscle and joint function during activities of daily living, and to assess the capacity of generic and scaled-generic musculotendon parameters to predict Muscle and joint function. Three-dimensional musculoskeletal models of the Shoulders of 6 healthy subjects were developed to calculate Muscle and glenohumeral joint loading during abduction, flexion, horizontal flexion, nose touching and reaching using subject-specific, scaled-generic and generic musculotendon parameters. Muscle and glenohumeral joint forces calculated using generic and scaled-generic models were significantly different to those of subject-specific models (p<0.05), and task dependent; however, scaled-generic model calculations of Shoulder glenohumeral joint force demonstrated better agreement with those of subject-specific models during abduction and flexion. Muscles in generic musculoskeletal models operated further from the plateau of their force–length curves than those of scaled-generic and subject-specific models, while Muscles in subject-specific models operated over a wider region of their force length curves than those of the generic or scaled-generic models, reflecting diversity of subject Shoulder strength. The findings of this study suggest that generic and scaled-generic musculotendon parameters may not provide sufficient accuracy in prediction of Shoulder Muscle and joint loading when compared to models that employ subject-specific parameter-estimation approaches.
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Shoulder Muscle function depends on elbow joint position: an illustration of dynamic coupling in the upper limb.
Journal of biomechanics, 2011Co-Authors: David C. Ackland, Marcus G. PandyAbstract:Shoulder Muscle function has been documented based on Muscle moment arms, lines of action and Muscle contributions to contact force at the glenohumeral joint. At present, however, the contributions of individual Muscles to Shoulder joint motion have not been investigated, and the effects of Shoulder and elbow joint position on Shoulder Muscle function are not well understood. The aims of this study were to compute the contributions of individual Muscles to motion of the glenohumeral joint during abduction, and to examine the effect of elbow flexion on Shoulder Muscle function. A three-dimensional musculoskeletal model of the upper limb was used to determine the contributions of 18 major Muscles and Muscle sub-regions of the Shoulder to glenohumeral joint motion during abduction. Muscle function was found to depend strongly on both Shoulder and elbow joint positions. When the elbow was extended, the middle and anterior deltoid and supraspinatus were the greatest contributors to angular acceleration of the Shoulder in abduction. In contrast, when the elbow was flexed at 90°, the anterior deltoid and subscapularis were the greatest contributors to joint angular acceleration in abduction. This dependence of Shoulder Muscle function on elbow joint position is explained by the existence of dynamic coupling in multi-joint musculoskeletal systems. The extent to which dynamic coupling affects Shoulder Muscle function, and therefore movement control, is determined by the structure of the inverse mass matrix, which depends on the configuration of the joints. The data provided may assist in the diagnosis of abnormal Shoulder function, for example, due to Muscle paralysis or in the case of full-thickness rotator cuff tears.
Clark R. Dickerson - One of the best experts on this subject based on the ideXlab platform.
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spatial dependency of Shoulder Muscle demands in horizontal pushing and pulling
Applied Ergonomics, 2012Co-Authors: Alison C Mcdonald, Bryan R Picco, Alicia L Belbeck, Amy Chow, Clark R. DickersonAbstract:Pushing and pulling account for nearly half of all manual material handling tasks. The purpose of this investigation was to develop a 3-D spatial Muscle activity map for the right upper extremity during pushing and pulling tasks. Nineteen males performed 140 ramped directional hand exertions (70 push; 70 pull) at locations along three axes aligned with the anatomical planes. Electromyography (EMG) of 14 sites on the right upper extremity was recorded. Two directional 3-way repeated measures ANOVAs assessed the influence of hand position on EMG. Hand position and exertion direction influenced total and individual Muscle demand. During pulling exertions, all three hand location parameters influenced total Muscle activity (p < 0.001) and similarly in pushing exertions (p < 0.002), though less pronounced than in pulling. Data were used to create equations to predict the Muscle activity of untested hand locations for novel work design scenarios.
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Upper limb posture and submaximal hand tasks influence Shoulder Muscle activity
International Journal of Industrial Ergonomics, 2010Co-Authors: Rebecca L. Brookham, Joanna M. Wong, Clark R. DickersonAbstract:Abstract The aim of this study was to investigate the effects of a light hand tool exertion task on Shoulder Muscle activation during different postures of Shoulder flexion and humeral rotation. The use of hand tools is linked with many cumulative trauma disorders of the upper extremity ( Chaffin et al., 2006 ). Generally, there was an increase in Muscle activity as the degree of Shoulder flexion increased. Pectoralis major and inferior trapezius emerged as major contributors in internal and external rotation, respectively. Generally, the inferior trapezius reached greater levels of activation than the other eight recorded Shoulder Muscles, and exceeded suggested activation recommendations ( Jonsson, 1978 ). Common industry and ergonomic guidelines suggest a general posture of reduced Shoulder flexion and neutral humeral rotation. Our results suggest that in order to reduce risky levels of inferior trapezius activation, light hand tool tasks (such as drilling) should be performed at neutral elevation and −45° internal rotation, or for slightly higher activations (but still low risk) at 60° Shoulder flexion and −45° internal rotation. Relevance to industry Identification of Muscle activation patterns with respect to posture and hand forces during light hand tool tasks helps establish work layout geometries in job design, and will provide the worker increased work endurance with lower risk exposures during task performance.
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quantifying scapula orientation and its influence on maximal hand force capability and Shoulder Muscle activity
Clinical Biomechanics, 2010Co-Authors: Bryan R Picco, Steven L Fischer, Clark R. DickersonAbstract:Abstract Background Non-neutral scapular orientations are often implicated as potential causes of Shoulder pathologies. However, their specific influence on Shoulder functional capabilities is largely unknown. This study objectively measured scapular orientation and quantified its influence on Shoulder Muscle activity levels and hand force capabilities during vertical and horizontal manual exertions. Methods Ten healthy male university students performed 24 exertions in combinations of scapular orientation (protracted, neutral and retracted), exertion direction (up, down, medial, lateral) and intensity (maximal or 40 N). Scapular orientation was quantified using an acromion marker cluster method. An orientation by intensity repeated measures ANOVA identified differences in quantified scapular orientation. A two-way multivariate ANOVA identified the influence of scapular orientation and hand force direction on Muscle activity and hand force capability. Findings Participants assumed consistent retracted, neutral, and protracted scapular orientations during exertions, and these three orientations were different from each other ( F (2, 99) = 158.57; P -value: 0.0001). Scapular orientation and exertion direction influenced Muscle recruitment almost universally ( P -value: 0.05). Scapular orientation did not influence hand force capability ( F (2, 99)=1.34; P -value: 0.05), but a hand force direction effect on force existed ( F (3, 99)=144.19; P -value: 0.0001). Interpretation These findings support recommendations of health practitioners who advocate neutral scapular orientations to reduce injury risk, as a neutral orientation achieved a balanced overall Muscle use pattern between retraction and protraction. Also, lowered Muscle activity and higher maximal forces suggest that downward exertion forces may be preferable when possible.
Peter Vee Sin Lee - One of the best experts on this subject based on the ideXlab platform.
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Modulation of Shoulder Muscle and joint function using a powered upper-limb exoskeleton.
Journal of biomechanics, 2018Co-Authors: Justin Fong, Vincent Crocher, Peter Vee Sin Lee, Denny Oetomo, Ying Tan, David C. AcklandAbstract:Abstract Robotic-assistive exoskeletons can enable frequent repetitive movements without the presence of a full-time therapist; however, human-machine interaction and the capacity of powered exoskeletons to attenuate Shoulder Muscle and joint loading is poorly understood. This study aimed to quantify Shoulder Muscle and joint force during assisted activities of daily living using a powered robotic upper limb exoskeleton (ArmeoPower, Hocoma). Six healthy male subjects performed abduction, flexion, horizontal flexion, reaching and nose touching activities. These tasks were repeated under two conditions: (i) the exoskeleton compensating only for its own weight, and (ii) the exoskeleton providing full upper limb gravity compensation (i.e., weightlessness). Muscle EMG, joint kinematics and joint torques were simultaneously recorded, and Shoulder Muscle and joint forces calculated using personalized musculoskeletal models of each subject’s upper limb. The exoskeleton reduced peak joint torques, Muscle forces and joint loading by up to 74.8% (0.113 Nm/kg), 88.8% (5.8%BW) and 68.4% (75.6%BW), respectively, with the degree of load attenuation strongly task dependent. The peak compressive, anterior and superior glenohumeral joint force during assisted nose touching was 36.4% (24.6%BW), 72.4% (13.1%BW) and 85.0% (17.2%BW) lower than that during unassisted nose touching, respectively. The present study showed that upper limb weight compensation using an assistive exoskeleton may increase glenohumeral joint stability, since deltoid Muscle force, which is the primary contributor to superior glenohumeral joint shear, is attenuated; however, prominent exoskeleton interaction moments are required to position and control the upper limb in space, even under full gravity compensation conditions. The modeling framework and results may be useful in planning targeted upper limb robotic rehabilitation tasks.
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The sensitivity of Shoulder Muscle and joint force predictions to changes in joint kinematics: A Monte-Carlo analysis.
Gait & posture, 2017Co-Authors: Peter Vee Sin Lee, David C. AcklandAbstract:Kinematics of the Shoulder girdle obtained from non-invasive measurement systems such as video motion analysis, accelerometers and magnetic tracking sensors has been shown to be adversely affected by instrumentation measurement errors and skin motion artefact. The degree to which musculoskeletal model calculations of Shoulder Muscle and joint loading are influenced by variations in joint kinematics is currently not well understood. A three-dimensional musculoskeletal model of the upper limb was used to evaluate the sensitivity of Shoulder Muscle and joint force. Monte-Carlo analyses were performed by randomly perturbing scapular and humeral joint coordinates during abduction and flexion. Muscle and joint force calculations were generally most sensitive to changes in the kinematics of the humerus in elevation and of the scapula in medial-lateral rotation, and were least sensitive to changes in humerus plane of elevation and scapula protraction-retraction. Overall model sensitivity was greater during abduction than flexion, and the influence of specific kinematics perturbations varied from Muscle to Muscle. In general, Muscles that generated greater force, such as the middle deltoid and subscapularis, were more sensitive to changes in Shoulder kinematics. This study suggests that musculoskeletal model sensitivity to changes in kinematics is task-specific, and varies depending on the plane of motion. Calculations of Shoulder Muscle and joint function depend on reliable humeral and scapula motion data, particularly that of humeral elevation and scapula medial-lateral rotation. The findings in this study have implications for the use of kinematic data in musculoskeletal model development and simulations.
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subject specific musculoskeletal modeling in the evaluation of Shoulder Muscle and joint function
Journal of Biomechanics, 2016Co-Authors: Peter Vee Sin Lee, Adam L Bryant, Mary P Galea, David C. AcklandAbstract:Upper limb Muscle force estimation using Hill-type Muscle models depends on musculotendon parameter values, which cannot be readily measured non-invasively. Generic and scaled-generic parameters may be quickly and easily employed, but these approaches do not account for an individual subject’s joint torque capacity. The objective of the present study was to develop a subject-specific experimental testing and modeling framework to evaluate Shoulder Muscle and joint function during activities of daily living, and to assess the capacity of generic and scaled-generic musculotendon parameters to predict Muscle and joint function. Three-dimensional musculoskeletal models of the Shoulders of 6 healthy subjects were developed to calculate Muscle and glenohumeral joint loading during abduction, flexion, horizontal flexion, nose touching and reaching using subject-specific, scaled-generic and generic musculotendon parameters. Muscle and glenohumeral joint forces calculated using generic and scaled-generic models were significantly different to those of subject-specific models (p<0.05), and task dependent; however, scaled-generic model calculations of Shoulder glenohumeral joint force demonstrated better agreement with those of subject-specific models during abduction and flexion. Muscles in generic musculoskeletal models operated further from the plateau of their force–length curves than those of scaled-generic and subject-specific models, while Muscles in subject-specific models operated over a wider region of their force length curves than those of the generic or scaled-generic models, reflecting diversity of subject Shoulder strength. The findings of this study suggest that generic and scaled-generic musculotendon parameters may not provide sufficient accuracy in prediction of Shoulder Muscle and joint loading when compared to models that employ subject-specific parameter-estimation approaches.
Ian Cathers - One of the best experts on this subject based on the ideXlab platform.
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Shoulder Muscle activation patterns and levels differ between open and closed-chain abduction.
Journal of science and medicine in sport, 2017Co-Authors: Darren Reed, Mark Halaki, Ian Cathers, Karen A. GinnAbstract:Abstract Objectives Open and closed-chain abduction of the Shoulder are commonly used in rehabilitation and exercise programs to assess and/or improve Shoulder Muscle function. However, it is not known if Shoulder Muscle activation patterns differ between these two exercises. Therefore the purpose of this study was to compare Muscle activation patterns during closed-chain Shoulder abduction performed using a Shoulder press machine with open-chain abduction using free weights. Design Experimental study. Methods Open and closed-chain abduction were performed by 15 and 14 subjects respectively at low (25%), medium (50%) and high (75%) load. Surface and indwelling electrodes were used to record the activation pattern of seven Shoulder Muscles during the concentric phase of each exercise. Data were normalised to maximum voluntary contractions (MVC), time normalised and compared over the common range of motion (40°–140° abduction). Results Only the activation pattern of middle deltoid had a strong positive correlation between exercises (r ≥ 0.65, p Conclusions Open-chain abduction is required to facilitate the stabilising role of the rotator cuff and axioscapular Muscles, in response to middle deltoid activity. Closed-chain exercises may enable full range Shoulder abduction earlier in rehabilitation programs, with an inherent stability and less demand on the rotator cuff.
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Does changing the plane of abduction influence Shoulder Muscle recruitment patterns in healthy individuals
Manual therapy, 2015Co-Authors: Darren Reed, Mark Halaki, Ian Cathers, Karen A. GinnAbstract:Abstract Study design Observational laboratory study. Background Abduction is a movement commonly used in the assessment of Shoulder dysfunction and prescription of exercises to improve Shoulder function. Abduction in the scapular and coronal planes are used interchangeably. It is not known if the activation of individual Shoulder Muscles differ between abduction performed in these planes and therefore, if they represent different tests/exercises. Objective To quantify and compare the Muscle activation patterns and levels for each Shoulder Muscle during abduction performed in the scapular plane with that performed in the coronal (scapular −30°) and scapular +30° planes. Methods Electromyographic recordings were taken from eight Shoulder Muscles of fourteen healthy volunteers during Shoulder abduction in the scapular and coronal planes and in a plane 30° anterior to the scapular plane (scapular +30°) at 50% of maximum load. Results Similar average Muscle activation levels were demonstrated during abduction in the scapular plane and within a 30° arc of this plane for all Muscles except: middle deltoid (5% MVC higher activation in the coronal and 4% MVC lower activation in the scapular +30° plane) and upper trapezius (6% MVC lower activation in the scapular +30° plane). Activation patterns between planes for all Muscles were similar (ICC (3,1) ≥ 0.87). Conclusions Abduction can be performed within a 30° arc of the scapular plane with no change in Shoulder Muscle activation patterns. Only middle deltoid activation levels change between the scapular and coronal planes and middle deltoid and upper trapezius between the scapular and scapular +30° planes.
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The role of Shoulder Muscles is task specific
Journal of science and medicine in sport, 2010Co-Authors: Craig E Boettcher, Ian Cathers, Karen A. GinnAbstract:Abstract The aim of this study was to compare activity in Shoulder Muscles during unsupported internal and external rotation to examine their functional roles, and determine whether they retain their ‘stabiliser’ or ‘mover’ role regardless of the Shoulder task. Electromyographic recordings in the dominant Shoulder of 15 normal subjects were taken from 13 Shoulder Muscle sites using a combination of surface and intramuscular electrodes during isometric Shoulder internal and external rotation in an unsupported abducted position under conditions of increasing load. During internal rotation significantly higher activity levels were found in subscapularis ( p p r 2 = 0.93 ± 0.07; mean ± s.d.). This study has shown that Shoulder Muscle function is task specific and that Shoulder Muscle motor strategy for a particular task does not change with increasing torque. As the only Shoulder rotators that demonstrated direction specificity the rotator cuff Muscles are likely to be functioning to provide rotation torque while the deltoid is likely to be providing dynamic Shoulder stability during the task examined. Higher scapulothoracic Muscle activity during external rotation indicated the need for greater dynamic scapular stability as a result of higher rotator cuff activity during external than internal rotation.
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standard maximum isometric voluntary contraction tests for normalizing Shoulder Muscle emg
Journal of Orthopaedic Research, 2008Co-Authors: Craig E Boettcher, Karen A. Ginn, Ian CathersAbstract:A comparison of electromyographic (EMG) activity of Muscles between and within subjects, and during separate occasions of testing, requires normalization. The most common way for generating the reference level used for normalizing Shoulder EMG data is with a maximum isometric voluntary contraction (MVIC). The purpose of this study was to develop a parsimonious set of standardized tests that generate an MVIC in all the major Muscle groups of the Shoulder. Twelve Muscles of the dominant Shoulder of 15 subjects were examined using a combination of surface and intramuscular electrodes during 15 tests. The results indicated that many tests maximally activated more than one Muscle simultaneously. Four tests were identified as being sufficient for generating an MVIC in the 12 Muscles examined and are recommended as the standard set for normalizing Shoulder Muscle EMG: abduction 90° with internal rotation (“empty can”), internal rotation in 90° abduction (“internal rotation 90°”), flexion at 125° with scapula resistance (“flexion 125°”), and horizontal adduction at 90° flexion (“palm press”). The use of these Shoulder normalization tests will make comparisons between Shoulder EMG studies more reliable. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res
Noriaki Ichihashi - One of the best experts on this subject based on the ideXlab platform.
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comparison of Shoulder Muscle strength cross sectional area acromiohumeral distance and thickness of the supraspinatus tendon between symptomatic and asymptomatic patients with rotator cuff tears
Journal of Shoulder and Elbow Surgery, 2020Co-Authors: Yasuyuki Ueda, Hiroaki Inui, Katsuya Nobuhara, Hiroshi Tanaka, Jun Umehara, Koji Tomita, Takashi Tachibana, Noriaki IchihashiAbstract:Background The purpose of this study was to demonstrate the differences in Shoulder Muscle strength, cross-sectional area of the rotator cuff Muscles, acromiohumeral distance, and supraspinatus tendon thickness between symptomatic and asymptomatic patients with rotator cuff tears. Methods Thirty-two symptomatic patients and 23 asymptomatic patients with rotator cuff tears participated in this study. Data of the patients with any type of tear and supraspinatus tear were analyzed. We evaluated the isometric torque, cross-sectional area of the rotator cuff Muscles, supraspinatus tendon thickness, acromiohumeral distance, range of motion, and Western Ontario Rotator Cuff Index. Results Asymptomatic patients showed greater isometric torque of Shoulder abduction and internal rotation than symptomatic patients with any type of tear (P ≤ .01). Asymptomatic patients also demonstrated greater cross-sectional area of the supraspinatus (P Conclusion Asymptomatic patients showed greater Shoulder range of motion, Muscle strength of Shoulder abduction and internal rotation, small occupation ratio of supraspinatus tendon thickness as a percentage of acromiohumeral distance, and large cross-sectional area of supraspinatus.
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Scapular kinematic and Shoulder Muscle activity alterations after serratus anterior Muscle fatigue.
Journal of shoulder and elbow surgery, 2018Co-Authors: Jun Umehara, Ken Kusano, Masatoshi Nakamura, Katsuyuki Morishita, Satoru Nishishita, Hiroki Tanaka, Itsuroh Shimizu, Noriaki IchihashiAbstract:Background Although the serratus anterior Muscle has an important role in scapular movement, no study to date has investigated the effect of serratus anterior fatigue on scapular kinematics and Shoulder Muscle activity. The purpose of this study was to clarify the effect of serratus anterior fatigue on scapular movement and Shoulder Muscle activity. Methods The study participants were 16 healthy men. Electrical Muscle stimulation was used to fatigue the serratus anterior Muscle. Shoulder Muscle strength and endurance, scapular movement, and Muscle activity were measured before and after the fatigue task. The Muscle activity of the serratus anterior, upper and lower trapezius, anterior and middle deltoid, and infraspinatus Muscles was recorded, and the median power frequency of these Muscles was calculated to examine the degree of Muscle fatigue. Results The Muscle endurance and median power frequency of the serratus anterior Muscle decreased after the fatigue tasks, whereas the Muscle activities of the serratus anterior, upper trapezius, and infraspinatus Muscles increased. External rotation of the scapula at the Shoulder elevated position increased after the fatigue task. Conclusion Selective serratus anterior fatigue due to electric Muscle stimulation decreased the serratus anterior endurance at the flexed Shoulder position. Furthermore, the Muscle activities of the serratus anterior, upper trapezius, and infraspinatus increased and the scapular external rotation was greater after serratus anterior fatigue. These results suggest that the rotator cuff and scapular Muscle compensated to avoid the increase in internal rotation of the scapula caused by the dysfunction of the serratus anterior Muscle.
