Left Anterior Deltoid Research Articles

Influence of different passive shoulder exoskeletons on shoulder and torso muscle activation during simulated horizontal and vertical aircraft squeeze riveting tasks

Aircraft manufacturing involves riveting utilizing squeeze riveting tools at heights from below elbow to overhead levels. This study assessed utilization of passive shoulder exoskeletons on shoulder and torso muscle activation during simulated squeeze riveting. Horizontal and vertical riveting tasks using squeeze riveting tools were performed by 16 aircraft workers wearing three different shoulder exoskeletons and a no-exoskeleton condition capturing electromyographic signals from shoulder and torso muscles. Exoskeletons reduced normalized EMG for the left anterior deltoid at both heights (6.6% and 15.7%), the right anterior deltoid (8.3%) and the right and left medial deltoid (9.3% and 8.9%) at the upper height for horizontal squeeze riveting. Exoskeletons reduced normalized EMG for the right and left anterior deltoids (7.0%–10.6%) and medial deltoids (1.3%–7.1%) within the upper zones during vertical squeeze riveting. Participants felt exoskeletons would be beneficial for squeeze riveting, however no preference was found among the exoskeletons used.

Changes in steering performance and muscle activity of the upper extremity according to the position of the spinner knob

Introduction A spinner knob attached to the steering wheel enables one-handed driving. However, changes in steering performance and muscle activity of the upper extremity based on the differences in the position of the knob are unknown. Aim To quantify changes in steering performance and their muscle activity according to the position of the knob. Method Twenty right-handed healthy men with a mean age of 30.9 years participated in the study. Steering operation (reaction time, accuracy, right-left balance and adaptability) as assessed by steering with both hands and left one-handed driving with the spinner knob at three positions (8, 10, and 12 o'clock) were evaluated using a driving simulator. Muscle activities of the left anterior deltoid, biceps brachii and long head of the triceps brachii during the simulated tasks were also recorded using a wireless surface electromyography. Results Muscle activity while steering with the knob at 8 o'clock was significantly lower than with the knob at 10 or 12 o'clock, and was equivalent to the steering performance and muscle activity when driving with both hands. On the other hand, muscle activity while driving with the knob at 10 o'clock was significantly higher than with the knob in the other positions. Conclusion The present study provides basic data for determining the position of the spinner knob attached to the steering wheel when driving one-handed with the non-dominant left hand. Positioning of the knob at 8 o'clock can be recommended on the basis of steering performance and lower muscle activities. IMPLICATIONS FOR REHABILITATION The safe driving of an automobile requires the driver to have an adequate range of motion and advanced voluntary motor control of the upper and lower extremities. When steering with the bilateral hands becomes difficult and driving with one-hand is required, it is necessary to attach a spinner knob on the steering wheel. This study provides objective and valuable information for clinicians and therapists to determine the optimum position of the spinner knob.

The "Nipple Whipple"?! A Pilot Study to Assess the Ergonomic Effects of Nipple-Sparing Mastectomy.

Nipple-sparing mastectomies (NSMs) with reconstruction are believed to be more difficult to perform than skin-sparing mastectomies (SSMs), but there is little quantitative data to support this claim. This prospective study analyzed four surgeons performing mastectomies. Electromyography (EMG) electrodes placed on selected muscle groups on each surgeon were used to capture muscle exertion intraoperatively and a percentage of maximum voluntary exertion was calculated (%MVE). Data regarding surgeon demographics, exercise habits, musculoskeletal problems, and surgery-specific workload was collected using a questionnaire. A total of 61 mastectomies were analyzed; 40 were NSM and 21 were SSM/total mastectomies. NSM were considered to be more mentally demanding and physically demanding than SSM (p < 0.001). When the surgeons' EMG data was analyzed as a group, there was a statistically significant difference in %MVE for NSM versus SSM at high muscle activity in bilateral anterior deltoid muscle groups and at average muscle activity for the left anterior deltoid muscle only. At low muscle activity, there was a statistically significant increase in activation for SSM versus NSM in bilateral cervical erector spinae. Repeated measures ANOVA was performed, which showed statistically significant differences at high muscle activity between NSM and SSM in the left cervical erector spinae and bilateral anterior deltoid muscles. Our pilot study shows that intraoperative EMGs can assess muscle activity for mastectomy operations and show a difference between NSM and SSM. This is the first study to provide quantitative data on muscle strain with NSM.

Does the use of an armrest modify upper extremity muscle demands during lateral sitting transfers in manual wheelchair users living with spinal cord injury?

Performing sitting transfers figures among the most demanding activities in manual wheelchair users living with spinal cord injury (MWU SCI ). Surprisingly, little is known about how the built environment may change movement strategies and upper extremity (UE) muscle demands during transfers. This study aims to determine to what extent the use of an armrest changes UE muscle demands during lateral sitting transfers in MWU SCI . Twenty MWU SCI performed lateral transfers toward the left under three experimental conditions: 1. without armrest, 2. with a left armrest at 9 cm, 3. with a left armrest at 18 cm above seat surface. Bilateral recorded EMG signals of the anterior deltoid, pectoralis major, biceps, and triceps were selected for analysis. Muscular utilization ratio (MUR) was obtained through amplitude-normalization using maximum voluntary contractions. Peak MUR and area under the MUR curve (AUC) of each muscle were compared across conditions using a non-parametric ANOVA. When transferring using the 9-cm armrest, the peak MUR increased in both triceps and decreased in left anterior deltoid, while the AUC decreased in right biceps compared to transfers without armrest. When transferring using the 18-cm armrest, the peak MUR increased in both triceps and decreased in left anterior deltoid and biceps, while AUC decreased in both biceps compared to transfers without armrest. Furthermore, the peak MUR increased in left pectoralis major compared to transfers using the 9-cm armrest. The use of an armrest during sitting transfers shifts part of the UE muscle demands from the shoulder flexors to the elbow extensors in MWU SCI . This adaptation may be linked to a reduced forward trunk flexion during transfer, although a confirmatory kinematic analysis is needed. Nonetheless, the availability of an armrest during transfers provides additional opportunities to vary UE muscle demands and to minimize UE musculoskeletal risk exposure.

A Comparison of Examination Equipment Used During Common Clinical Ophthalmologic Tasks

OCCUPATIONAL APPLICATIONS Ophthalmologists and other eye-care physicians frequently use clinical examination equipment that restricts access to patients and requires the adoption of sustained, non-neutral working postures of the neck and shoulders. The use of ergonomic principles in the design of examination equipment could help reduce these physical demands, which may be partly responsible for the high prevalence of neck and shoulder pain among ophthalmologists. This study compared the effects of a set of this alternative “ergonomic” equipment to a set of conventional equipment on measures of neck and shoulder muscle activity and upper arm posture during simulations of common clinical ophthalmologic tasks. Results suggested that some aspects of the alternative equipment may help reduce exposures to sustained, non-neutral working postures of the neck and shoulder among ophthalmologists. Ophthalmologists and other eye-care physicians may consider implementing similar alternative equipment interventions into their practices.TECHNICAL ABSTRACT Background: Ophthalmologists report a high prevalence of work-related musculoskeletal symptoms, particularly of the neck and shoulders. Improving the design of equipment used in the clinical environment may reduce exposures to physical risk factors (e.g., sustained muscular exertions and non-neutral postures) associated with neck and shoulder pain among ophthalmologists. Purpose: This study compares estimates of neck and shoulder muscle activity and upper arm posture during use of conventional and alternative examination equipment common in clinical ophthalmologic practice. Methods: Fifteen ophthalmologists performed one mock clinical examination using conventional equipment and one mock clinical examination using alternative equipment with the potential to reduce exposure to sustained muscular exertions and non-neutral upper arm postures. The alternative equipment included a slit lamp biomicroscope with inclined viewing oculars, adjustable elbow supports, and a wider tabletop with more room for supporting the arms in comparison to the conventional slit lamp biomicroscope. A wireless binocular indirect ophthalmoscope was also evaluated that had a more even weight distribution than the conventional design. Measurements of upper trapezius and anterior deltoid muscle activity, upper arm posture, and perceived usability were used to compare the conventional and alternative equipment. Results: In comparison to the conventional slit lamp biomicroscope, the alternative slit lamp biomicroscope led to (i) 12% to 13% reductions in upper trapezius muscle activity levels, (ii) a 9% reduction in left anterior deltoid muscle activity levels, and (iii) a 15% reduction in the percentage of work time spent with the left upper arm elevated in positions greater than 60º. In addition, participants rated the comfort and adjustability of both the alternative slit lamp biomicroscope and binocular indirect ophthalmoscope more favorably than the conventional equipment. Conclusions: The results suggest that the alternative slit lamp biomicroscope may help to reduce overall muscular demands and non-neutral postures of the neck and shoulder region among ophthalmologists.

The role of anticipatory postural adjustments in interlimb coordination of coupled arm movements in the parasagittal plane: II. Postural activities and coupling coordination during cyclic flexion–extension arm movements, ISO- and ANTI-directionally coupled

When coupling cyclic adduction-abduction movements of the arms in the transverse (horizontal) plane, isodirectional (ISO) coupling is less stable than antidirectional (ANTI) coupling. We proposed that such deficiency stems from the disturbing action that anticipatory postural adjustments exert on ISO coupling. To ascertain if postural adjustments differentiate ISO versus ANTI coupling coordination in other types of cyclic arm movements, we examined flexion-extension oscillations in the parasagittal plane. Oscillations of the right arm alone elicited cyclic Postural Adjustments (PAs) in the left Anterior Deltoid and Posterior Deltoid, which replicated the excitation-inhibition pattern of the prime movers right Anterior Deltoid, right Posterior Deltoid. Cyclic PAs also developed symmetrically in Erector Spinae (RES and LES) and in phase opposition in Ischiocruralis (RIC and LIC), so as to discharge to the ground both an anteroposterior force, Fy, and a moment about the vertical axis, Tz. Oscillations of both arms in ISO coupling induced symmetric PAs in both ES and IC muscles, thus generating a large Fy but no Tz. In ANTI coupling, PAs in RES and LES remained symmetric but smaller in size, while PAs in RIC and LIC were large and opposite in phase, resulting in a large Tz and small Fy. Altogether, PAs would thus favour ISO and hamper ANTI parasagittal movements because (1) in the motor pathways to the prime movers of either arm, a convergence would occur between the voluntary commands and the commands for PAs linked to the movement of the other arm, the two commands having the same sign (excitatory or inhibitory) during ISO and an opposite sign during ANTI; (2) the postural effort of trunk and leg muscles would be higher for generating Tz in ANTI than Fy in ISO. These predictions fit with the finding that coupling stability was lower in ANTI than in ISO, i.e., opposite to horizontal movements. In conclusion, in both parasagittal and horizontal arm movements, the less coordinated coupling mode was the one constrained by postural adjustments through the two above mechanisms.

Co-activation of primary motor cortex ipsilateral to muscles contracting in a unilateral motor task

ObjectiveThis study aims to investigate the role of the primary motor cortex ipsilateral to the movement (ipsilateral M1) in unilateral motor execution. MethodsFifteen right-handed healthy subjects underwent functional magnetic resonance imaging (fMRI) and transcranial magnetic stimulation (TMS) experiments. Motor tasks were performed with the right-side limb. Subjects followed visual cues to execute movements in the scanner and independent component analysis (ICA) was applied to analyse the data. Interhemispheric inhibition (IHI), short-interval intracortical inhibition (SICI) and recruitment curves (RCs) of motor-evoked potentials (MEPs) in right M1 were measured by TMS and responses were recorded from the left flexor carpi radialis (FCR) and left anterior deltoid (AD). ResultsGroup ICA showed activations of bilateral M1s highly related to motor tasks. Additionally, TMS results showed significant increases of MEP RCs on the left FCR and left AD during right wrist flexion and right shoulder flexion. Prominent decreases of IHI and SICI were also observed under the same conditions. ConclusionsDuring unilateral muscle contraction, co-activation of the ipsilateral M1 involves additional processes modulated by intra- and interhemispheric interactions and its size of activations is specifically enhanced on the homotopic representation. SignificanceThe ipsilateral M1 plays a central role in unilateral motor executions.

Cortico-cortical properties in Parsonage-Turner Syndrome: a TMS case study

We report the long-term effects of one unilateral Parsonage-Turner Syndrome case (PTS) on motor cortex representation of a proximal upper limb muscle. The subject suffered from a sporadic painful episode of weakness of the shoulder girdle muscles seven years earlier. At this time, needle EMG recordings showed only few MUs in the left anterior deltoid muscle (AD), while nerve conduction was found normal. Arthroscanner examination was unremarkable confirming the absence of joint lesion. The episode lasted for one year.