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1.
Ann Work Expo Health ; 2019 Nov 30.
Artigo em Inglês | MEDLINE | ID: mdl-31785202

RESUMO

OBJECTIVES: Varied work-related musculoskeletal disorders (WMSDs) claim rates were found between companies even when they were in the same sectors with similar sizes. This study aimed to (i) identify common risk factors for back, shoulder, hand/wrist, and knee WMSDs among manufacturing jobs, and (ii) characterize the biomechanical exposures in jobs and work organizational practices between high and low WMSD claim rate companies so that more focused, industry-specific intervention strategies may be developed. METHODS: Using historical workers' compensation data, manufacturing companies were divided into two paired groups (low and high in the lower 25%ile and higher 75%ile, respectively). On-site job evaluations were conducted in 16 companies to determine job biomechanical risk levels. Management and workers' representatives in 32 paired companies were interviewed to identify possible differences between management strategies and management/worker relationships. A total of 39 injured workers were also interviewed to gather information of self-reported injury causes and suggested preventive measures. RESULTS: Analyses of 432 job evaluations showed that more jobs had higher risk levels of prolonged standing and heavy lifting in the high back WMSD claim rate companies than the low claim rate ones. No high biomechanical risk factors were found to be associated with jobs in high shoulder claim rate companies. High repetition, pinch force, and Strain Index were associated with high hand/wrist WMSD claim rate companies. High work pace and job stress were common among high knee WMSD claim rate companies. There were no statistically significant differences for the organizational factors between high and low WMSD claim rate companies. Heavy lifting, fast work pace, high hand/wrist repetition, high hand force, and awkward shoulder postures were identified as major contributing factors by the injured workers. CONCLUSIONS: High WMSD claim rate companies appeared to have more high biomechanical exposure jobs than low WMSD claim rate companies. Available job evaluation methods for the low back and hand/wrists are satisfactory in quantifying job risk levels in the manufacturing industry. Research into more sensitive job evaluation methods for the shoulder and knee are needed.

2.
Urol Int ; : 1-10, 2019 Dec 05.
Artigo em Inglês | MEDLINE | ID: mdl-31805567

RESUMO

Urolithiasis is one of the most common urologic diseases in industrialized societies. More than 80% of renal stones are composed of calcium oxalate, and small changes in urinary oxalate concentrations affect the risk of stone formation. Elucidation of the source of oxalate and its mechanism of transport is crucial for understanding the etiology of urolithiasis. Sources of oxalate can be both endogenous and exogenous. With regard to oxalate transport, tests were carried out to prove the function of solute-linked carrier 4 (SLC4) and SLC26. The molecular mechanism of urolithiasis caused by SLC4 and SLC26 is still unclear. The growing number of studies on the molecular physiology of SLC4 and SLC26, together with knockout genetic mouse model experiments, suggest that SLC4 and SLC26 may be a contributing element to urolithiasis. This review summarizes recent research on the sources of oxalate and characterization of the oxalate transport ionic exchangers SLC4 and SLC26, with an emphasis on different physiological defects in knockout mouse models including kidney stone formation. Furthermore, SLC4 and SLC26 exchangers provide new insight into urolithiasis and may be a novel therapeutic target for modification of urinary oxalate excretion.

3.
Work ; 64(3): 563-568, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31658089

RESUMO

BACKGROUND: Sit-stand workstations have been introduced in the workplaces to address the adverse sedentary effect inherent to typical office jobs. Existing field or laboratory studies showed that standing interventions are not a detriment to work productivity or performance. The effect of gradient standing proportion on these measures is still unknown. OBJECTIVE: The current naturalistic pilot study aimed to examine the controlled sit-stand ratio effect on office performances. METHODS: Eleven musculoskeletal symptom free office employees from a large government agency volunteered in this study. They were all equipped with electronic sit-stand desks. Computer usage (N=11) and productivity (N=3) were collected using software and organizational metrics, respectively, for four typical workdays of four different sit-stand ratios (7 : 1, 3 : 1, 2 : 1, and 1 : 1). RESULTS: There were no statistically significant schedule effects on any computer usage measures. While not significant, time using computer, keystrokes, word count, and keyboard errors were all less as standing time increased. Sit-stand ratio and job productivity did not observe a clear cause and effect relationship. CONCLUSIONS: The amount of time spent standing in typical office jobs might not affect computer usage and productivity. Further study with a larger sample is needed for a stronger evidence.

4.
Appl Ergon ; 75: 129-133, 2019 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-30509517

RESUMO

Cranking the landing gear is a common task performed by truck drivers to raise or lower trailers. This task poses a risk to the shoulder joint due to the required forceful exertion and the posture constrained to the hand-handle interface. As a potential occupational risk, there has been no definitive guideline for best practices among truck drivers. An operator can crank perpendicular (frontal) or parallel (sagittal) to the crank rotation. In this laboratory study, the effects of cranking method and resistance on scapular range of motion and shoulder muscle activity were observed in 12 participants. Scapular posture was measured using an optical motion tracking system. EMG was monitored on 16 muscles contributing to shoulder movement. The results show that during frontal cranking, the scapular range of protraction was 28 ±â€¯11.6°, which was more than the sagittal cranking (23 ±â€¯10.4°), indicating a decreased subacromial space and elevated shoulder impingement risk. Seven muscles (all three deltoid muscles, middle trapezius, supraspinatus, infraspinatus, and teres minor) demonstrated that when the crank resistance was low, the front cranking method resulted in lower activity than the side cranking. When the crank resistance was 20 Nm, the muscle activity on these seven muscles was greater when cranking from the front than from the side. Based on these observations, we suggest that when the resistance is low (lowering the trailer) the driver should stand facing the trailer. On the contrary, it is advantageous to stand parallel to the trailer and crank while raising the trailer to apply the full body strength to reduce the shoulder load.


Assuntos
Sistemas Homem-Máquina , Escápula/fisiologia , Adulto , Ergonomia , Mãos/fisiologia , Humanos , Masculino , Movimento , Esforço Físico/fisiologia , Postura/fisiologia , Amplitude de Movimento Articular , Rotação , Articulação do Ombro/fisiologia , Análise e Desempenho de Tarefas
5.
Hum Factors ; 61(1): 64-77, 2019 02.
Artigo em Inglês | MEDLINE | ID: mdl-30091947

RESUMO

OBJECTIVE: A method for automatically classifying lifting postures from simple features in video recordings was developed and tested. We explored if an "elastic" rectangular bounding box, drawn tightly around the subject, can be used for classifying standing, stooping, and squatting at the lift origin and destination. BACKGROUND: Current marker-less video tracking methods depend on a priori skeletal human models, which are prone to error from poor illumination, obstructions, and difficulty placing cameras in the field. Robust computer vision algorithms based on spatiotemporal features were previously applied for evaluating repetitive motion tasks, exertion frequency, and duty cycle. METHODS: Mannequin poses were systematically generated using the Michigan 3DSSPP software for a wide range of hand locations and lifting postures. The stature-normalized height and width of a bounding box were measured in the sagittal plane and when rotated horizontally by 30°. After randomly ordering the data, a classification and regression tree algorithm was trained to classify the lifting postures. RESULTS: The resulting tree had four levels and four splits, misclassifying 0.36% training-set cases. The algorithm was tested using 30 video clips of industrial lifting tasks, misclassifying 3.33% test-set cases. The sensitivity and specificity, respectively, were 100.0% and 100.0% for squatting, 90.0% and 100.0% for stooping, and 100.0% and 95.0% for standing. CONCLUSIONS: The tree classification algorithm is capable of classifying lifting postures based only on dimensions of bounding boxes. APPLICATIONS: It is anticipated that this practical algorithm can be implemented on handheld devices such as a smartphone, making it readily accessible to practitioners.

7.
Ergonomics ; 61(2): 243-254, 2018 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-28689467

RESUMO

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.


Assuntos
Edema/etiologia , , Decoração de Interiores e Mobiliário , Dor Musculoesquelética/etiologia , Postura , Local de Trabalho , Adulto , Terminais de Computador , Eletromiografia , Feminino , Humanos , Masculino , Fadiga Muscular , Saúde do Trabalhador , Músculos Paraespinais/fisiopatologia , Coluna Vertebral/fisiopatologia , Músculos Superficiais do Dorso/fisiopatologia , Fatores de Tempo
8.
Appl Ergon ; 65: 418-423, 2017 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-28395854

RESUMO

Shoulder joint kinematics has been used as a representative indicator to investigate musculoskeletal symptoms among computer users for office ergonomics studies. The traditional measurement of shoulder kinematics normally requires a laboratory-based motion tracking system which limits the field studies. In the current study, a portable, low cost, and marker-less Microsoft Kinect™ sensor was examined for its feasibility on shoulder kinematics measurement during computer tasks. Eleven healthy participants performed a standardized computer task, and their shoulder kinematics data were measured by a Kinect sensor and a motion tracking system concurrently. The results indicated that placing the Kinect sensor in front of the participants would yielded a more accurate shoulder kinematics measurements then placing the Kinect sensor 15° or 30° to one side. The results also showed that the Kinect sensor had a better estimate on shoulder flexion/extension, compared with shoulder adduction/abduction and shoulder axial rotation. The RMSE of front-placed Kinect sensor on shoulder flexion/extension was less than 10° for both the right and the left shoulder. The measurement error of the front-placed Kinect sensor on the shoulder adduction/abduction was approximately 10° to 15°, and the magnitude of error is proportional to the magnitude of that joint angle. After the calibration, the RMSE on shoulder adduction/abduction were less than 10° based on an independent dataset of 5 additional participants. For shoulder axial rotation, the RMSE of front-placed Kinect sensor ranged between approximately 15° to 30°. The results of the study suggest that the Kinect sensor can provide some insight on shoulder kinematics for improving office ergonomics.


Assuntos
Técnicas Biossensoriais/instrumentação , Ergonomia/instrumentação , Articulação do Ombro/fisiologia , Interface Usuário-Computador , Trabalho/fisiologia , Adulto , Fenômenos Biomecânicos , Técnicas Biossensoriais/métodos , Computadores , Ergonomia/métodos , Estudos de Viabilidade , Feminino , Voluntários Saudáveis , Humanos , Masculino , Amplitude de Movimento Articular , Reprodutibilidade dos Testes
9.
J Electromyogr Kinesiol ; 33: 103-110, 2017 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-28232284

RESUMO

Optimization combined with a musculoskeletal shoulder model has been used to estimate mechanical loading of musculoskeletal elements around the shoulder. Traditionally, the objective function is to minimize the summation of the total activities of the muscles with forces, moments, and stability constraints. Such an objective function, however, tends to neglect the antagonist muscle co-contraction. In this study, an objective function including an entropy term is proposed to address muscle co-contractions. A musculoskeletal shoulder model is developed to apply the proposed objective function. To find the optimal weight for the entropy term, an experiment was conducted. In the experiment, participants generated various 3-D shoulder moments in six shoulder postures. The surface EMG of 8 shoulder muscles was measured and compared with the predicted muscle activities based on the proposed objective function using Bhattacharyya distance and concordance ratio under different weight of the entropy term. The results show that a small weight of the entropy term can improve the predictability of the model in terms of muscle activities. Such a result suggests that the concept of entropy could be helpful for further understanding the mechanism of muscle co-contractions as well as developing a shoulder biomechanical model with greater validity.


Assuntos
Entropia , Modelos Biológicos , Músculo Esquelético/fisiologia , Ombro/fisiologia , Adulto , Fenômenos Biomecânicos , Eletromiografia , Feminino , Humanos , Masculino , Contração Muscular , Postura , Articulação do Ombro/fisiologia
10.
J Electromyogr Kinesiol ; 29: 28-33, 2016 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-26253991

RESUMO

The movements of the humerus, the clavicle, and the scapula are not completely independent. The coupled pattern of movement of these bones is called the shoulder rhythm. To date, multiple studies have focused on providing regression-based 3-D shoulder rhythms, in which the orientations of the clavicle and the scapula are estimated by the orientation of the humerus. In this study, six existing regression-based shoulder rhythms were evaluated by an independent dataset in terms of their predictability. The datasets include the measured orientations of the humerus, the clavicle, and the scapula of 14 participants over 118 different upper arm postures. The predicted orientations of the clavicle and the scapula were derived from applying those regression-based shoulder rhythms to the humerus orientation. The results indicated that none of those regression-based shoulder rhythms provides consistently more accurate results than the others. For all the joint angles and all the shoulder rhythms, the RMSE are all greater than 5°. Among those shoulder rhythms, the scapula lateral/medial rotation has the strongest correlation between the predicted and the measured angles, while the other thoracoclavicular and thoracoscapular bone orientation angles only showed a weak to moderate correlation. Since the regression-based shoulder rhythm has been adopted for shoulder biomechanical models to estimate shoulder muscle activities and structure loads, there needs to be further investigation on how the predicted error from the shoulder rhythm affects the output of the biomechanical model.


Assuntos
Imagem Tridimensional/métodos , Movimento/fisiologia , Ombro/diagnóstico por imagem , Ombro/fisiologia , Adulto , Fenômenos Biomecânicos/fisiologia , Clavícula/diagnóstico por imagem , Clavícula/fisiologia , Feminino , Humanos , Úmero/diagnóstico por imagem , Úmero/fisiologia , Masculino , Amplitude de Movimento Articular/fisiologia , Escápula/diagnóstico por imagem , Escápula/fisiologia , Articulação do Ombro/diagnóstico por imagem , Articulação do Ombro/fisiologia
11.
Ergonomics ; 59(4): 526-33, 2016 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-26189639

RESUMO

We assess the one-handed static pull strength of a Chinese population and compare it to that of an American sample. Fifty men and 50 women in five age groups were asked to exert their maximum one-handed pull strength in three pulling directions (across, front and side) and from four pulling heights (61 cm, 76 cm, waist height and above-shoulder height). The results showed that women had less pull strength than men under all of the conditions tested. The front and side pulling resulted in the greatest pull strength, with a decrease detected when the pulling height was increased. The American sample exhibited greater strength than the Chinese. Body mass and men's handgrip force were also associated with the pull strength. These variables should be taken into account in the development of tasks related to one-handed pulling. Practitioner summary: In this paper, we report a laboratory-based experiment conducted to assess the one-handed static pull strength of a Chinese population and compare the results with those of an American population. The variables associated with pull strength included gender, pulling direction, pulling height, race, body mass and men's handgrip force.


Assuntos
Braço/fisiologia , Grupo com Ancestrais do Continente Asiático , Força Muscular/fisiologia , Adolescente , Adulto , Índice de Massa Corporal , China , Feminino , Força da Mão/fisiologia , Humanos , Masculino , Pessoa de Meia-Idade , Valores de Referência , Fatores Sexuais , Estados Unidos , Adulto Jovem
12.
Exp Gerontol ; 70: 150-6, 2015 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-26315289

RESUMO

BACKGROUND: The number of drivers over 65 years of age continues to increase. Although neck rotation range has been identified as a factor associated with self-reported crash history in older drivers, it was not consistently reported as indicators of older driver performance or crashes across previous studies. It is likely that drivers use neck and trunk rotation when driving, and therefore the functional range of motion (ROM) (i.e. overall rotation used during a task) of older drivers should be further examined. OBJECTIVE: Evaluate older driver performance in an immersive virtual reality, simulated, dynamic driving blind spot target detection task. METHODS: A cross-sectional laboratory study recruited twenty-six licensed drivers (14 young between 18 and 35 years, and 12 older between 65 to 75 years) from the local community. Participants were asked to detect targets by performing blind spot check movements while neck and trunk rotation was tracked. Functional ROM, target detection success, and time to detection were analyzed. RESULTS: In addition to neck rotation, older and younger drivers on average rotated their trunks 9.96° and 18.04°, respectively. The younger drivers generally demonstrated 15.6° greater functional ROM (p<.001), were nearly twice as successful in target detection due to target location (p=.008), and had 0.46 s less target detection time (p=.016) than the older drivers. CONCLUSION: Assessing older driver functional ROM may provide more comprehensive assessment of driving ability than neck ROM. Target detection success and time to detection may also be part of the aging process as these measures differed between driver groups.


Assuntos
Envelhecimento/fisiologia , Condução de Veículo , Pescoço/fisiologia , Amplitude de Movimento Articular/fisiologia , Adolescente , Adulto , Idoso , Condução de Veículo/psicologia , Estudos Transversais , Feminino , Humanos , Masculino , Desempenho Psicomotor , Rotação , Análise e Desempenho de Tarefas , Interface Usuário-Computador , Adulto Jovem
13.
Gait Posture ; 42(2): 145-51, 2015 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-26002604

RESUMO

The measurement of gait parameters normally requires motion tracking systems combined with force plates, which limits the measurement to laboratory settings. In some recent studies, the possibility of using the portable, low cost, and marker-less Microsoft Kinect sensor to measure gait parameters on over-ground walking has been examined. The current study further examined the accuracy level of the Kinect sensor for assessment of various gait parameters during treadmill walking under different walking speeds. Twenty healthy participants walked on the treadmill and their full body kinematics data were measured by a Kinect sensor and a motion tracking system, concurrently. Spatiotemporal gait parameters and knee and hip joint angles were extracted from the two devices and were compared. The results showed that the accuracy levels when using the Kinect sensor varied across the gait parameters. Average heel strike frame errors were 0.18 and 0.30 frames for the right and left foot, respectively, while average toe off frame errors were -2.25 and -2.61 frames, respectively, across all participants and all walking speeds. The temporal gait parameters based purely on heel strike have less error than the temporal gait parameters based on toe off. The Kinect sensor can follow the trend of the joint trajectories for the knee and hip joints, though there was substantial error in magnitudes. The walking speed was also found to significantly affect the identified timing of toe off. The results of the study suggest that the Kinect sensor may be used as an alternative device to measure some gait parameters for treadmill walking, depending on the desired accuracy level.


Assuntos
Fenômenos Biomecânicos/fisiologia , Marcha/fisiologia , Articulação do Quadril/fisiologia , Articulação do Joelho/fisiologia , Processamento de Sinais Assistido por Computador/instrumentação , Caminhada/fisiologia , Adolescente , Adulto , Algoritmos , Teste de Esforço/instrumentação , Feminino , Humanos , Masculino , Valores de Referência , Reprodutibilidade dos Testes , Adulto Jovem
14.
J Biomech ; 48(4): 721-4, 2015 Feb 26.
Artigo em Inglês | MEDLINE | ID: mdl-25636855

RESUMO

An inertial sensor-embedded virtual reality (VR) head-mounted display, the Oculus Rift (the Rift), monitors head movement so the content displayed can be updated accordingly. While the Rift may have potential use in cervical spine biomechanics studies, its accuracy in terms of cervical spine mobility measurement has not yet been validated. In the current study, a VR environment was designed to guide participants to perform prescribed neck movements. The cervical spine kinematics was measured by both the Rift and a reference motion tracking system. Comparison of the kinematics data between the Rift and the tracking system indicated that the Rift can provide good estimates on full range of motion (from one side to the other side) during the performed task. Because of inertial sensor drifting, the unilateral range of motion (from one side to neutral posture) derived from the Rift is more erroneous. The root-mean-square errors over a 1-min task were within 10° for each rotation axis. The error analysis further indicated that the inertial sensor drifted approximately 6° at the beginning of a trial during the initialization. This needs to be addressed when using the Rift in order to more accurately measure cervical spine kinematics. It is suggested that the front cover of the Rift should be aligned against a vertical plane during its initialization.


Assuntos
Vértebras Cervicais/fisiologia , Movimento/fisiologia , Pescoço/fisiologia , Amplitude de Movimento Articular/fisiologia , Interface Usuário-Computador , Adulto , Idoso , Fenômenos Biomecânicos , Feminino , Movimentos da Cabeça/fisiologia , Humanos , Masculino , Pessoa de Meia-Idade , Modelos Biológicos , Reprodutibilidade dos Testes , Rotação
15.
Ergonomics ; 57(8): 1201-12, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-24800641

RESUMO

Age may modify the association between occupational physical demand and muscle loading, and ultimately increase the risk of musculoskeletal disorders. The goal of this study was to investigate age-related differences in shoulder muscle fatigue development during a repetitive manual task. Twenty participants in two age groups completed an 80-minute simulated low-intensity assembly task. Electromyographic (EMG) manifestation of muscle fatigue was observed in the upper trapezius, deltoid and infraspinatus muscles in both age groups, and coincided with an increase in the subjective ratings of perceived exertions. Compared with the younger group, older group showed a more monotonic decrease in EMG power frequency in the upper trapezius and deltoid muscles. However, the age-related difference in EMG amplitude was less consistent. Relative rest time of the upper trapezius muscle in the older group was less than the young group throughout the task. The observed patterns of EMG measures suggest that older participants may have disadvantages in fatigue resistance in the upper trapezius and posterior deltoid muscles during the simulated repetitive manual task.


Assuntos
Fatores Etários , Músculo Deltoide/fisiopatologia , Fadiga Muscular , Músculos Superficiais do Dorso/fisiopatologia , Adulto , Idoso , Eletromiografia , Humanos , Contração Isométrica , Pessoa de Meia-Idade , Esforço Físico , Ombro , Análise e Desempenho de Tarefas , Adulto Jovem
16.
Molecules ; 19(6): 6911-28, 2014 May 26.
Artigo em Inglês | MEDLINE | ID: mdl-24865603

RESUMO

This research attempted to study the effect of lipophilicity on the anticancer activity of N-substituted norcantharimide derivatives. Twenty-three compounds were synthesized and their cytotoxicities against five human cancer cell lines studied. The lipophilicity of each derivative was altered by its substituent, an alkyl, alkyloxy, terpenyl or terpenyloxy group at the N-position of norcantharimide. Further, among all synthesized derivatives studied, the compounds N-farnesyloxy-7-oxabicyclo[2.2.1]heptane-2,3-dicarboximide (9), and N-farnesyl-7-oxabicyclo[2.2.1]heptane-2,3-dicarboximide (18), have shown the highest cytotoxicity, anti-proliferative and apoptotic effect against human liver carcinoma HepG2 cell lines, yet displayed no significant cytotoxic effect on normal murine embryonic liver BNL CL.2 cells. Their overall performance led us to believe that these two compounds might be potential candidates for anticancer drugs development.


Assuntos
Antineoplásicos/síntese química , Compostos Bicíclicos Heterocíclicos com Pontes/química , Animais , Antineoplásicos/química , Antineoplásicos/farmacologia , Apoptose/efeitos dos fármacos , Linhagem Celular , Proliferação de Células/efeitos dos fármacos , Células Hep G2 , Humanos , Camundongos
17.
J Electromyogr Kinesiol ; 24(3): 419-29, 2014 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-24618104

RESUMO

Tissue overloading is a major contributor to shoulder musculoskeletal injuries. Previous studies attempted to use regression-based methods to predict muscle activities from shoulder kinematics and shoulder kinetics. While a regression-based method can address co-contraction of the antagonist muscles as opposed to the optimization method, most of these regression models were based on limited shoulder postures. The purpose of this study was to develop a set of regression equations to predict the 10th percentile, the median, and the 90th percentile of normalized electromyography (nEMG) activities from shoulder postures and net shoulder moments. Forty participants generated various 3-D shoulder moments at 96 static postures. The nEMG of 16 shoulder muscles was measured and the 3-D net shoulder moment was calculated using a static biomechanical model. A stepwise regression was used to derive the regression equations. The results indicated the measured range of the 3-D shoulder moment in this study was similar to those observed during work requiring light physical capacity. The r(2) of all the regression equations ranged between 0.228 and 0.818. For the median of the nEMG, the average r(2) among all 16 muscles was 0.645, and the five muscles with the greatest r(2) were the three deltoids, supraspinatus, and infraspinatus. The results can be used by practitioners to estimate the range of the shoulder muscle activities given a specific arm posture and net shoulder moment.


Assuntos
Braço/fisiologia , Contração Isométrica/fisiologia , Modelos Biológicos , Músculo Esquelético/fisiologia , Postura/fisiologia , Análise de Regressão , Ombro/fisiologia , Adulto , Fenômenos Biomecânicos , Eletromiografia , Feminino , Humanos , Masculino , Músculos/fisiologia , Valores de Referência , Trabalho
18.
J Electromyogr Kinesiol ; 24(3): 404-11, 2014 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-24642235

RESUMO

Repetitive low-force contractions are common in the workplace and yet can lead to muscle fatigue and work-related musculoskeletal disorders. The current study aimed to investigate potential motion adaptations during a simulated repetitive light assembly work task designed to fatigue the shoulder region, focusing on changes over time and age-related group differences. Ten younger and ten older participants performed four 20-min task sessions separated by short breaks. Mean and variability of joint angles and scapular elevation, joint net moments for the shoulder, elbow, and wrist were calculated from upper extremity kinematics recorded by a motion tracking system. Results showed that joint angle and joint torque decreased across sessions and across multiple joints and segments. Increased kinematic variability over time was observed in the shoulder joint; however, decreased kinematic variability over time was seen in the more distal part of the upper limb. The changes of motion adaptations were sensitive to the task-break schedule. The results suggested that kinematic and kinetic adaptations occurred to reduce the biomechanical loading on the fatigued shoulder region. In addition, the kinematic and kinetic responses at the elbow and wrist joints also changed, possibly to compensate for the increased variability caused by the shoulder joint while still maintaining task requirements. These motion strategies in responses to muscle fatigue were similar between two age groups although the older group showed more effort in adaptation than the younger in terms of magnitude and affected body parts.


Assuntos
Movimento/fisiologia , Fadiga Muscular/fisiologia , Músculo Esquelético/fisiologia , Análise e Desempenho de Tarefas , Extremidade Superior/fisiologia , Adaptação Fisiológica/fisiologia , Adulto , Idoso , Fenômenos Biomecânicos , Cotovelo/fisiologia , Feminino , Humanos , Cinética , Pessoa de Meia-Idade , Pronação/fisiologia , Amplitude de Movimento Articular/fisiologia , Tempo de Reação , Rotação , Ombro/fisiologia , Torque , Trabalho , Punho/fisiologia , Adulto Jovem
19.
J Biomech ; 47(5): 1206-10, 2014 Mar 21.
Artigo em Inglês | MEDLINE | ID: mdl-24534377

RESUMO

In biomechanical modeling of the shoulder, it is important to know the orientation of each bone in the shoulder girdle when estimating the loads on each musculoskeletal element. However, because of the soft tissue overlying the bones, it is difficult to accurately derive the orientation of the clavicle and scapula using surface markers during dynamic movement. The purpose of this study is to develop two regression models which predict the orientation of the clavicle and the scapula. The first regression model uses humerus orientation and individual factors such as age, gender, and anthropometry data as the predictors. The second regression model includes only the humerus orientation as the predictor. Thirty-eight participants performed 118 static postures covering the volume of the right hand reach. The orientation of the thorax, clavicle, scapula and humerus were measured with a motion tracking system. Regression analysis was performed on the Euler angles decomposed from the orientation of each bone from 26 randomly selected participants. The regression models were then validated with the remaining 12 participants. The results indicate that for the first model, the r(2) of the predicted orientation of the clavicle and the scapula ranged between 0.31 and 0.65, and the RMSE obtained from the validation dataset ranged from 6.92° to 10.39°. For the second model, the r(2) ranged between 0.19 and 0.57, and the RMSE obtained from the validation dataset ranged from 6.62° and 11.13°. The derived regression-based shoulder rhythm could be useful in future biomechanical modeling of the shoulder.


Assuntos
Modelos Biológicos , Articulação do Ombro/fisiologia , Adulto , Braço , Fenômenos Biomecânicos , Clavícula , Feminino , Humanos , Úmero , Masculino , Movimento (Física) , Movimento , Postura , Amplitude de Movimento Articular , Análise de Regressão , Escápula , Ombro , Tórax , Adulto Jovem
20.
J Orthop Res ; 32(4): 524-30, 2014 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-24391059

RESUMO

Elevated carpal tunnel pressure (CTP) has been associated with carpal tunnel syndrome. This study systematically evaluated the effect of wrist motion resistance and grip type on CTP during wrist motion typical of occupational tasks. CTP during four wrist motion patterns, with and without resistance, and with and without gripping, was measured in vivo in 14 healthy individuals. CTP measured during compound motions fell between that measured in the cardinal planes of wrist flexion/extension and radial/ulnar deviation. Generally, with no active gripping there was little pressure change due to wrist angular displacement or resistance level. However, concurrent active pinch or power grip increased CTP particularly in motions including extension. CTP typically did not increase during wrist flexion, and in fact often decreased. Extension motions against resistance when employing a pinch or power grip increase CTP more than motions with flexion. Results could help inform design or modification of wrist motion intensive occupational tasks. © 2014 The Authors.


Assuntos
Articulação do Punho/fisiologia , Adulto , Síndrome do Túnel Carpal/etiologia , Feminino , Voluntários Saudáveis , Humanos , Masculino , Pressão , Amplitude de Movimento Articular , Adulto Jovem
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