Posture Of Upper Limb Research Articles

Elbow angle modulates corticospinal excitability to the resting biceps brachii at both spinal and supraspinal levels.

What is the central question of this study? Corticospinal excitability to biceps brachii is known to modulate according to upper-limb posture. Here, cervicomedullary stimulation was used to investigate potential spinal contributions to elbow angle-dependent changes in corticospinal excitability at rest. What is the main finding and its importance? At more extended elbow angles, biceps responses to cervicomedullary stimulation were decreased, whereas cortically evoked responses (normalized to cervicomedullary-evoked responses) were increased. Results suggest decreased spinal excitability but increased cortical excitability as the elbow is placed in a more extended position, an effect that is unlikely to be attributable to cutaneous stretch receptor activation. Corticospinal excitability to biceps brachii is known to modulate according to upper-limb posture. In study1, our aim was to investigate potential spinal contributions to this modulation and the independent effect of elbow angle. Biceps responses to transcranial magnetic stimulation (motor evoked potentials; MEPs) and electrical cervicomedullary stimulation (cervicomedullary motor evoked potentials; CMEPs) were measured at five elbow angles ranging from full extension to 130deg of flexion. In study2, possible contributions of cutaneous stretch receptors to elbow angle-dependent excitability changes were investigated by eliciting MEPs and CMEPs in three conditions of skin stretch about the elbow (stretch to mimic full extension, no stretch or stretch to mimic flexion). Each study had 12 participants. Evoked potentials were acquired at rest, with participants seated, the shoulder flexed 90deg and forearm supinated. The MEPs and CMEPs were normalized to maximal compound muscle action potentials. In study1, as the elbow was moved to more extended positions, there were no changes in MEPs (P=0.963), progressive decreases in CMEPs (P<0.0001; CMEPs at 130deg flexion ∼220% of full extension) and increases in the MEP/CMEP ratio (P=0.019; MEP/CMEP at 130deg flexion ∼20% of full extension). In study2, there were no changes in MEPs (P=0.830) or CMEPs (P=0.209) between skin stretch conditions. Therefore, although results suggest a decrease in spinal and an increase in supraspinal excitability at more extended angles, the mechanism for these changes in corticospinal excitability to biceps is not cutaneous stretch receptor feedback.

Effect of assistive devices on hand and arm posture during activities of daily living

Assistive devices (ADs) are products designed to overcome the grip strength and mobility difficulties produced by ageing and different pathologies. Nevertheless, little is known about the postural effect of such devices. This work aims to quantify this effect on the entire upper limb. Ten healthy right-handed subjects performed 13 activities of daily living (ADL) with normal products and 22 ADs and both arm (shoulder, elbow and wrist) and hand (grasp types and contacts) postures were analysed. ADs were found to affect upper limb postures in ADL, reducing the use of precision grasps in the right hand by 31.9% and increasing palm contact by 26% and 29.1% in right and left hands, respectively. Nevertheless, they were also found to increase shoulder flexion, elbow pronation and wrist deviation, which may be a drawback in some pathologies. Results may help in the selection of a suitable AD for enhancing ADL performance depending on the patient's limitations due to a particular pathology.

Workstation configuration and container type influence upper limb posture in grocery bagging

IntroductionRepetitive movements and awkward postures are two persistent injury risk factors for grocery store cashiers. Due to the recent rise in popularity of environmentally-friendly grocery bagging options, current recommendations for cashiers are likely outdated. Correspondingly, the objective of this study was to examine the effects of cashier-specific work demands, workstation configuration, and container type on upper limb postures during typical job activities. MethodsFifteen experienced cashiers bagged groceries at varying combinations of workstation height (low, medium, high) and container type (reusable bins, reusable bags, plastic bags). Upper limb movement was quantified with motion capture and amplitude probability distribution functions of humeral elevation and humeral axial internal rotation were used to assess the static (10th percentile), median (50th percentile), and peak (90th percentile) postural demands, which were then interpreted in the context of existing postural guidelines. ResultsHigh workstation height and reusable bags increased right arm elevation at peak posture by 15.7° compared to the low workstation height and reusable bin combination. However, reusable bins increased internal rotation demands of the right arm by 4.3° compared to other container types. Left arm elevation and internal rotation were consistently lower than right arm angles. ConclusionCashiers are encouraged to adjust the workstation to decrease the arm elevation and internal rotation required by higher workstation heights and tall containers, and to use both arms for scanning and packing, when possible, to reduce undesirable arm postures.

Upper limb position sense quantification using robotics in patients with stroke: Preliminary results

Proprioceptive deficits affect around 50% of stroke survivors. Most commonly used proprioception assessments have poor psychometric properties and are not adapted for people with multiple impairments. To address these limitations, we developed an assessment protocol that enables the quantification of elbow position sense without using the opposite arm, involving active movement of the evaluated limb or relying on working memory. The objectives of this study were to quantify elbow position sense of stroke survivors and to compare it with a control group. Elbow position sense of the affected arm was quantified in subacute stroke patients and compared to age-matched healthy persons. Elbow position sense was evaluated using a KINARM exoskeleton and a virtual reality display. The exoskeleton passively moved the participant's arm from an initial to a target position (no visual cues of arm position). A virtual arm representation was then projected on a screen placed over the participant's arm. The participant had to indicate verbally its relative position (more flexed or more extended) compared to the virtual representation. A 75% detection threshold was extracted from a sigmoid curve fit representing the relationship between the angular difference and the percentage of successful trials. Independent T-tests were used to compare the results of both groups. Eleven people with a stroke (67 ± 9 yrs old; 6 males; 72 ± 30 days post-lesion) and 19 age-matched controls (63 ± 6 yrs old; 8 males) were recruited. A significant difference in the mean elbow position sense detection thresholds between the stroke group (12.8 ± 5.2 degrees) and the control group (7.2 ± 3.5 degrees) was noted ( P = 0.001). This robotic assessment enables the quantification of elbow position sense in patients with stroke. Difference in detection thresholds observed between both groups demonstrated that stroke survivors might have impaired proprioception. More participants are required to confirm these results.

Myoelectric Control Based on a Generic Musculoskeletal Model: Toward a Multi-User Neural-Machine Interface.

This paper aimed to develop a novel electromyography (EMG)-based neural-machine interface (NMI) that is user-generic for continuously predicting coordinated motion betweenmuscle contractionmetacarpophalangeal (MCP) and wrist flexion/extension. The NMI requires a minimum calibration procedure that only involves capturing maximal voluntary muscle contraction for themonitoredmuscles for individual users. At the center of the NMI is a user-generic musculoskeletal model based on the experimental data collected from six able-bodied (AB) subjects and nine different upper limb postures. The generic model was evaluated on-line on both AB subjects and a transradial amputee. The subjectswere instructed to performa virtual hand/wrist posture matching task with different upper limb postures. The on-line performanceof the genericmodelwas also compared with that of the musculoskeletal model customized to each individual user (called "specific model"). All subjects accomplished the assigned virtual tasks while using the user-generic NMI, although the AB subjects produced better performance than the amputee subject. Interestingly, compared with the specific model, the generic model produced comparable completion time, a reduced number of overshoots, and improved path efficiency in the virtual hand/wrist posture matching task. The results suggested that it is possible to design an EMG-driven NMI based on a musculoskeletalmodelthat could fit multiple users, including upper limb amputees, for predicting coordinated MCP and wrist motion. The present new method might address the challenges of existing advanced EMG-based NMI that require frequent and lengthy customization and calibration. Our future research will focus on evaluating the developed NMI for powered prosthetic arms.

Upper limb disorders and hand-arm vibration risks with hand-held olive beaters

Olive harvesting with hand-held beaters is a repetitive work, tiring and time consuming (more than 4–5 h/day). Operators work with vibrating tools in not natural body postures: they are therefore exposed to various risks, especially at the upper limbs. Unfortunately, also if in the agriculture sector the number of the declared upper limb disorders increased in the last years, hand-arm vibration and incongruent upper limb postures are not yet well perceived. In this work, the hand-arm vibration exposure and the OCRA index were calculated for five operators which used three different electric olive beaters. In all the observed tests both the hand-arm vibration and the OCRA scores produced results over the admitted limits. A(8) ranged between 8.6 ms-2 and 25.4 ms-2, far from the 5 ms-2 daily exposure limit values admitted by the European law (European Directive 2002/44). The OCRA checklist values ranged from a minimum value of 13.32 (red light level and light risk) for the left limb and a maximum of 34.41 (violet, high level and high risk) for the right limb. Relevance to industryThis paper describes the analysis of the combined risks to hand-arm vibration and to upper limb disorders in a typical agricultural harvesting task with a manual handled tool powered by electric engine. Tests were carried out during the olive harvesting with five operators using three different hand-held machines. Both vibration and OCRA parameters were acquired. Results showed that in all the observed tests both the hand-arm vibration and the OCRA scores were over the admitted limits. Beaters transmitted vibration to both the operators’ hand-arm system, but operators did not declare to perceive vibration at the right upper limb (because it was less affected by the vibration stimulus than the left one). To acquire reliable values for the upper limb biomechanical risk detection it should be necessary to use measured vibration data in field, avoiding personal judgments. When it is not possible to measure the vibration level, the employer should use the machine instruction, where the manufacturer should have written the vibration total value to which the hand-arm system is subjected, if it exceeds 2,5 m/s2 (European Directive 2006/42). When this information is not available in the machine instruction, the employer may refers to other sources (European Directive 2002/44), as databases provided by government or institutional bodies, including vibration values obtained by research specialists and vibration consultants.

A comparison of upper body and limb postures across technology and handheld device use in college students.

[Purpose] People using technology and handheld devices adopt postures of the upper limb and neck that could result in musculoskeletal pathology. Previous research has explored the postures assumed during isolated use of technology devices, such as a smartphone, however a comparison of posture assumed between multiple devices has not been completed. The purpose of this study was to compare the posture of the upper body and limb between handheld devices and technology. [Participants and Methods] Twenty one healthy college students completed this study. Pictures of participants were taken in a neutral posture and as they performed standard tasks with 3 devices (mobile phone, tablet, laptop). A mobile application calculated sagittal and coronal plane posture variables, which were compared between device conditions with an ANOVA and post-hoc tests. [Results] Head translation and angulation and shoulder angulation varied significantly between conditions in both planes. Shoulder translation varied significantly between conditions in the sagittal plane. Rib translation varied significantly between conditions in the coronal plane. Tablet use produced postures that were statistically different than the other devices. [Conclusion] Use of each device altered posture however, frequent, regular use of a tablet may produce greater deleterious effects than regular use of other handheld devices/technology.

Left subclavian artery malperfusion due to thoracic outlet syndrome during total vertebrectomy for invasive lung cancer: a case report

Thoracic outlet syndrome (TOS) can interrupt blood flow to upper limbs by vascular compression. We report a case of a 52-year-old man who presented left subclavian artery malperfusion due to TOS during total vertebrectomy (Th2–4) in the prone position for invasive lung cancer. At the time of resection of the vertebral bodies, his left radial systolic blood pressure had begun to drop intermittently and we noticed an interarm pressure difference. Accordingly, we began to monitor the right radial artery pressure and found that only the left radial artery pressure decreased as a result of compressive force from the surgical site. The operation was continued with intermittent malperfusion of the left arm, and when it was prolonged, we asked the surgeons to release the compression. No symptoms of ischemia or nerve injuries in the left arm were observed after the surgery. Retrospective review of his preoperative enhanced computed tomography images suggested a slightly compressed left subclavian artery in the costoclavicular space. Combination of the prone position and a specific upper limb position may be a risk factor for intraoperative TOS. An interarm blood pressure difference is a clue to detect accidental arterial TOS during general anesthesia.

Differences in ergonomic and workstation factors between computer office workers with and without reported musculoskeletal pain.

Some studies have suggested a causal relationship between computer work and the development of musculoskeletal disorders. However, studies considering the use of specific tools to assess workplace ergonomics and psychosocial factors in computer office workers with and without reported musculoskeletal pain are scarce. The aim of this study was to compare the ergonomic, physical, and psychosocial factors in computer office workers with and without reported musculoskeletal pain (MSP). Thirty-five computer office workers (aged 18-55 years) participated in the study. The following evaluations were completed: Rapid Upper Limb Assessment (RULA), Rapid Office Strain Assessment (ROSA), and Maastricht Upper Extremity Questionnaire revised Brazilian Portuguese version (MUEQ-Br revised). Student t-tests were used to make comparisons between groups. The computer office workers were divided into two groups: workers with reported MSP (WMSP, n = 17) and workers without positive report (WOMSP, n = 18). Those in the WMSP group showed significantly greater mean values in the total ROSA score (WMSP: 6.71 [CI95% :6.20-7.21] and WOMSP: 5.88 [CI95% :5.37-6.39], p = 0.01). The WMSP group also showed higher scores in the chair section of the ROSA, workstation of MUEQ-Br revised, and in the upper limb RULA score. The chair height and armrest sections from ROSA showed the higher mean values in workers WMSP compared to workers WOMSP. A positive moderate correlation was observed between ROSA and RULA total scores (R = 0.63, p < 0.001). Our results demonstrated that computer office workers who reported MSP had worse ergonomics indexes for chair workstation and worse physical risk related to upper limb (RULA upper limb section) than workers without pain. However, there were no observed differences in workers with and without MSP regarding work-related psychosocial factors. The results suggest that inadequate workstation conditions, specifically the chair height, arm and back rest, are linked to improper upper limb postures and that these factors are contributing to MSP in computer office workers.

Can the use of an alternatively designed tamper alter spine posture and risk of upper limb injury while tamping espresso?

Tamping is the process of compressing espresso grinds in order to pull shots of espresso and has been identified as one of the most strenuous tasks performed by baristas due to relatively high force and repetition as well as awkward spine and upper limb postures. Therefore, the current study aimed to determine if an alternatively designed tamper is able to alter spine posture and upper limb risk of risk while tamping. To test this, the current study measured 1) three-dimensional thoracic and lumbar spine posture using electromagnetic sensors adhered over the spine; 2) force applied to the tamper using a force plate; and 3) risk of upper limb injury using RULA and the Strain Index while tamping with a traditional vertical handle tamper and a flat handle-less tamper. Ten experienced baristas each performed 20 tamps (10 with the traditional tamper and 10 with the flat tamper; order randomized) of standard weight/grind espresso. Tamping with the flat tamper resulted in more neutral thoracic and lumbar spine postures and reduced force applied when using the flat tamper. The flat tamper also resulted in a lower score for both RULA and the Strain Index indicating a lower risk of injury to the upper limb. Based on the findings of this study, a flat, handle-less tamper has the potential to be a more ergonomically effective tool for tamping espresso grinds.

Assessment of upper limb musculoskeletal pain and posture in workers of packaging units of pharmaceutical industries.

Work-related musculoskeletal disorders are defined as the disabling or painful injury to the muscles, nerves or tendons that are caused by work or aggravated by it. Some studies confirm the association between working in packaging units in various industries and the pain in the upper limb, but also there are controversies about the possible risk factors among different working populations. The present study aims to define the potential ergonomic risk factors for musculoskeletal pain in the upper limb. The Nordic Musculoskeletal Questionnaire was used for assessment of the musculoskeletal pain. Some other questions about the possible risk factors were included in the questionnaire. In order to assess posture, rapid upper limb assessment (RULA) test was performed by trained ergonomists. The findings of the study reveals that shoulder pain is associated with work history (P-value = 0.01), smoking (P-value = 0.02), the level of education (P-value = 0.04) and age more than 40 years old (P-value = 0.01). Wrist pain was associated with shiftwork (P-value = 0.04) and especially fixed shiftwork (P-value = 0.04) and also age more than 40(P-value = 0.03) and missed days from work with a cut point of 7 days (P-value = 0.03). After regression, only the work history (OR = 14.4 for 10 to 20 years and OR = 32.2 for more than 20 years) and shiftwork (OR = 2.35) remained statistically significant. In this study, RULA was not associated with symptoms in the upper limb in non-heavy working industries so we do not recommend it for screening purposes. The use of decades of working history and shiftwork can be considered for this purpose in the shoulder and wrist pain respectively.

The influence of upper limb position on landing technique during a drop vertical jump

The influence of upper limb position on landing technique during a drop vertical jump

Limb-position robust classification of myoelectric signals for prosthesis control using sparse representations.

The fundamental objective in non-invasive myoelectric prosthesis control is to determine the user's intended movements from corresponding skin-surface recorded electromyographic (sEMG) activation signals as quickly and accurately as possible. Linear Discriminant Analysis (LDA) has emerged as the de facto standard for real-time movement classification due to its ease of use, calculation speed, and remarkable classification accuracy under controlled training conditions. However, performance of cluster-based methods like LDA for sEMG pattern recognition degrades significantly when real-world testing conditions do not resemble the trained conditions, limiting the utility of myoelectrically controlled prosthesis devices. We propose an enhanced classification method that is more robust to generic deviations from training conditions by constructing sparse representations of the input data dictionary comprised of sEMG time-frequency features. We apply our method in the context of upper-limb position changes to demonstrate pattern recognition robustness and improvement over LDA across discrete positions not explicitly trained. For single position training we report an accuracy improvement in untrained positions of 7.95%, p ≪ .001, in addition to significant accuracy improvements across all multiposition training conditions, p <; .001.

EEG-based BCI for the linear control of an upper-limb neuroprosthesis

Assistive technologies help patients to reacquire interacting capabilities with the environment and improve their quality of life. In this manuscript we present a feasibility study in which healthy users were able to use a non-invasive Motor Imagery (MI)-based brain computer interface (BCI) to achieve linear control of an upper-limb functional electrical stimulation (FES) controlled neuro-prosthesis. The linear control allowed the real-time computation of a continuous control signal that was used by the FES system to physically set the stimulation parameters to control the upper-limb position. Even if the nature of the task makes the operation very challenging, the participants achieved a mean selection accuracy of 82.5% in a target selection experiment. An analysis of limb kinematics as well as the positioning precision was performed, showing the viability of using a BCI–FES system to control upper-limb reaching movements. The results of this study constitute an accurate use of an online non-invasive BCI to operate a FES-neuroprosthesis setting a step toward the recovery of the control of an impaired limb with the sole use of brain activity.

Kufor–Rakeb syndrome (KRS): Clinico-radiological phenotype of a probable sporadic case with “eye of tiger” sign

Abstract Kufor–Rakeb syndrome (KRS) is a rare autosomal recessive form of pallidopyramidal degeneration, supranuclear upgaze paresis and cognitive decline, first described in Kufor–Rakeb. Disease pathogenesis of KRS is due to loss of function of ATP13A2 (PARK9) gene which was identified by Ramirez et al. A 24 years old adolescent male presented with one-year history of abnormal behavior followed by apathy since 3 months. Subsequently, he developed one episode of abrupt abnormal twisting posture of left upper limb and lower limb lasting for an hour which preceded slowness in his daily activities and anarthria. He also developed tremulousness in all four extremities and cognitive decline in the form of difficulty in simple calculation and naming. On neurological examination he had cognitive decline, supranuclear upgaze paresis, pyramidal features in the form of spasticity, hyperreflexia with extensor plantar response and extrapyramidal features in the form of tremor and myoclonus suggestive of facial-faucial-finger mini myoclonus (FFF mini myoclonus) without sensory involvement. MRI brain revealed bilateral cerebral, brainstem and cerebellar generalized atrophy and DWI showed hypo intensity in putamen and globus pallidus surrounding a hyperintense lesion like “eye of tiger” sign. He showed minimal improvement initially on trihexyphenidyl and levodopa plus carbidopa combination but response was not consistent on follow up and he became bed bound within one and half years after disease onset. In our patient dystonia was an early feature and interestingly MRI brain showed “eye of tiger” sign which has not been reported earlier in the literature.

OnabotulinumtoxinA Injection for Poststroke Upper-Limb Spasticity: Guidance for Early Injectors From a Delphi Panel Process

BackgroundOnabotulinumtoxinA reduces muscle hypertonia associated with poststroke spasticity (PSS). PSS manifests as several common postures. ObjectiveTo define treatment paradigms for PSS upper-limb common postures. DesignModified Delphi method. SettingExpert panel. ParticipantsTen injectors experienced in the treatment and clinical research of PSS (physiatrists and neurologists) were invited to participate in the Delphi panel. MethodsThe Delphi panel reviewed an electronic worksheet with PSS upper-limb postures to define onabotulinumtoxinA treatment paradigms (Round 1). During Round 2, panel members discussed in person Round 1 results and voted until consensus (≥66% agreement). Recommendations were geared toward those with new or early injection experience. Main Outcome MeasurementsExpert consensus on onabotulinumtoxinA treatment parameters for PSS including muscles to inject, dose per muscle and posture, and treatment adjustments for suboptimal response. ResultsFor each posture, consensus was reached on targeted subsets of muscles. Doses ranged for individual muscles (10-100 U) and total doses per posture (50-200 U). An onabotulinumtoxinA dilution 50 U/mL (2:1 dilution ratio) was considered most appropriate; dilution ratios of 1:1 to 4:1 may be appropriate in some circumstances. The majority (89%) of panel members would increase the dose and/or the number of muscles treated for a suboptimal response to onabotulinumtoxinA. The panel identified 3 common aggregate upper-limb postures: (1) adducted shoulder + flexed elbow + pronated forearm + flexed wrist + clenched fist; (2) flexed elbow + pronated forearm + flexed wrist + clenched fist; and (3) flexed wrist + clenched fist. The recommended starting dose per aggregate was 300 U, 300 U, and 200 U, with a total maximum dose of 400 U, 400 U, and 300 U, respectively. Localization guidance techniques were considered essential for all postures. ConclusionsConsensus on common muscles and onabotulinumtoxinA treatment paradigms for postures associated with upper-limb PSS was achieved via a modified Delphi method. The purpose of this analysis is to educate early onabotulinumtoxinA injectors rather than provide an evidence-based review. Level of EvidenceV

Evaluation of a Task-Based Intervention After Tendon Transfer to Restore Lateral Pinch

ObjectiveTo quantify changes in pinch force and brachioradialis (BR) activation after a task-based training program designed to improve pinch force after BR to flexor pollicis longus (FPL) transfer. DesignOne-group repeated-measures design compared pinch force and BR activation pre- and posttraining. Significant differences were tested with Wilcoxon signed-rank tests for pairwise comparisons at the P≤.05 level. SettingTesting occurred in a Veterans Affairs Medical Center research laboratory and training was in a home setting. ParticipantsParticipants with cervical spinal cord injury (SCI) and previous BR to FPL transfer were enrolled in the study (N=8). Six patients completed the training program and posttraining measures. InterventionsThe 10-week training was a home program that included novel activities to increase BR activation and practice producing pinch force in a variety of upper limb postures. Participants were provided with the task-based training equipment and instructed to practice 3 times per week. Main Outcome MeasuresFine-wire electromyography of the transferred BR was recorded in maximum effort pinch force (N). Secondary measures included the strength and activation of the antagonist elbow extensor. ResultsPinch force increased 3.7N (.38kg) and BR muscle activation increased 10% (P≤.05) after the training. There was no increase in elbow extension strength, but participants with previous posterior deltoid to triceps transfer achieved greater activation of the antagonist elbow extensor. ConclusionsThe findings from this pilot study suggest that outcomes of tendon transfer and conventional therapy can be improved for patients with chronic cervical SCI.

The effect of grip force, stroke rotation and frequency on discomfort for a torqueing tasks.

Occupational tasks involve awkward upper limb postures, especially movement of forearm with repetitive combined gripping and torqueing exertions, which may lead to development of WMSDs. From the literature survey it was observed that there was a lack of studies focussed on the combined effect of torque and grip exertions on forearm discomfort. The present study was to investigate the effects of grip force, stroke rotation and frequency of exertions on discomfort and Electromyography (EMG) activities of the forearm muscles in a repetitive torqueing task. Twenty-seven male participants volunteered in this study. The participants performed repetitive exertions for a 5 minutes duration for each combination of the different levels of stroke rotation, grip force and frequency of exertions. Three levels of stroke rotation, three levels of grip force and three levels of frequency of exertion were chosen as independent variables. Therefore a 3 × 3 customized factorial design was used for the experiment for each level of grip force. Hence, the study was divided into three groups on the basis of grip force (50N, 70N and 90N). The ANOVA showed that stroke rotation and frequency of exertion were significant on discomfort. Further Students Newmann test (SNK) revealed that discomfort was increased with increasing stroke rotation and frequency of exertion. The multivariate analysis of variances (MANOVA) performed on EMG data instead of ANOVA because EMG activities of five muscles simultaneously were recorded. The Results found that extensor muscles were more fatigued in torqueing with gripping task. It was found that stroke rotation for the torqueing tasks must be kept below 45°. It was concluded that it is important to control stroke rotation to improve performance of repetitive torqueing activity.

The effects of upper limb posture and a sub-maximal gripping task on corticospinal excitability to muscles of the forearm

Variations in handgrip force influences shoulder muscle activity, and this effect is dependent upon upper limb position. Previous work suggests that neural coupling between proximal and distal muscles with changes in joint position is a possible mechanism but these studies tend to use artificially constrained postures that do not reflect activities of daily living. The purpose of this study was to examine the effects of upper limb posture on corticospinal excitability to the forearm muscles during workplace relevant arm positions. Motor evoked potentials (MEPs) were elicited in four forearm muscles via transcranial magnetic stimulation at six arm positions (45°, 90° and 120° of humeral elevation in both the flexion and abduction planes). MEPs were delivered as stimulus–response curves (SRCs) at rest and at constant intensity during two gripping tasks. Boltzmann plateau levels were smaller for the flexor carpi radialis in flexion at 45° versus 90° (p=0.0008). Extensor carpi radialis had a greater plateau during flexion than abduction (p=0.0042). Corticospinal excitability to the forearm muscles were influenced by upper limb posture during both the resting and gripping conditions. This provides further evidence that upper limb movements are controlled as a whole rather than segmentally and is relevant for workplace design considerations.

Micro movements of the upper limb in fibromyalgia: The relation to proprioceptive accuracy and visual feedback

The purpose of this study was to explore the role of visual and proprioceptive feedback in upper limb posture control in fibromyalgia (FM) and to assess the coherence between acceleration measurements of upper limb micro movements and surface electromyography (sEMG) of shoulder muscle activity (upper trapezius and deltoid). Twenty-five female FM patients and 25 age- and sex-matched healthy controls (HCs) performed three precision motor tasks: (1) maintain a steady shoulder abduction angle of 45° while receiving visual feedback about upper arm position and supporting external loads (0.5, 1, or 2kg), (2) maintain the same shoulder abduction angle without visual feedback (eyes closed) and no external loading, and (3) a joint position sense test (i.e., assessment of proprioceptive accuracy). Patients had more extensive increase in movement variance than HCs when visual feedback was removed (P<0.03). Proprioceptive accuracy was related to movement variance in HCs (R⩾0.59, P⩽0.002), but not in patients (R⩽0.25, P⩾0.24). There was no difference between patients and HCs in coherence between sEMG and acceleration data. These results may indicate that FM patients are more dependent on visual feedback and less reliant on proprioceptive information for upper limb posture control compared to HCs.