Deltoid Muscle Research Articles

The effects of working with a passive arm-support exoskeleton on objective and self-reported measures during field tasks – a randomised cross-over study

Musculoskeletal disorders (MSDs) are prevalent under poor working situations. Where it is not possible to remove the root cause of MSDs, passive exoskeletons could be a solution. In this randomised cross-over field study we investigated the effect of a passive arm-support exoskeleton. Ten participants, recruited from a Dutch gas company, were measured with and without exoskeleton assessing muscle activity, heart rate (HR), arm elevation, and reported about their experiences. Participants spent more time in high arm elevation levels with the exoskeleton than without. Muscle activity was lower in the trapezius (Beta: −1.8 [−3.1; −0.4]) and deltoid (Beta: −1.4 [−2.3; −0.6]) muscles, but not the biceps muscle, during the measurements with exoskeleton than without, suggesting effectiveness of the exoskeleton. HR and discomfort did not statistically significantly differ between the two conditions. Participants would recommend an exoskeleton to their colleagues, but mainly for repetitive work. Their opinions about the usefulness during work varied.

Clinical outcome of elbow extension restoration by posterior deltoid-to-triceps transfer in tetraplegia: a retrospective review of 51 patients.

In this study, we report the functional and perceived outcomes of 51 posterior deltoid-to-triceps transfers in patients with tetraplegia. With a minimum follow-up of 12 months, patients were divided into two subcategories based on preoperative posterior deltoid strength: Medical Research Council (MRC) 3 and MRC 4/5. At 12-month follow-up, all patients achieved antigravity elbow extension. Patients with a stronger posterior deltoid (MRC 4/5) attained an elbow extension with a strength grade MRC 3.7 (SD 0.6), while those with a weaker posterior deltoid (MRC 3) reached an elbow extension of MRC 3.1 (SD 0.6). Patient-reported outcome measure was evaluated using the Canadian Occupational Performance Measure (COPM) and demonstrated a significant improvement for both performance and satisfaction. No difference in the COPM scores could be found between the two subcategories. This study indicates that tetraplegic patients with a posterior deltoid strength grade of both MRC 4/5 as well as MRC 3 benefit from the procedure.Level of evidence: III.

Effects of track-based stair climbing robot on muscle activity, usability, and psychological anxiety: a preliminary study

This study investigated the effects of using the LiftCar-150 track-based stair-climbing robot on muscle activity, usability, and psychological anxiety. While stair-climbing robots enhance mobility for individuals with physical disabilities, existing research has predominantly focused on engineering perspectives, with limited attention to user-centered outcomes. Ten healthy participants and an 80 kg dummy rider completed stair-climbing tasks at slow (5 m/min) and fast (7 m/min) speeds. Muscle activity in the middle trapezius (MT), erector spinae (ES), multifidus (MF), gluteus maximus (Gmax), gluteus medius (Gmed), and anterior deltoid (AD) muscles was recorded by electromyography. Usability was evaluated in terms of safety, efficiency, and satisfaction using a 5-point Likert scale, while psychological anxiety was assessed with a visual analog scale (VAS) ranging from 0 to 10. Results showed that during stair ascent, activities of the back extensors (ES and MF) and gluteus muscles (Gmax and Gmed) significantly increased compared to descent, while anterior deltoid activity was higher during descent. Usability scores averaged 4.05 for stability, 4.1 for efficiency, and 3.7 for satisfaction. Perceived psychological anxiety scores were 4.2 ± 0.3 and 5.4 ± 0.5 at slow speed, and 3.5 ± 0.2 and 5.7 ± 0.4 at fast speed during ascent and descent, respectively. While operators recognized the robot’s stability and efficiency, satisfaction levels were neutral, and specific muscle activation was increased. These findings provide essential insights into optimizing the design and usability of stair-climbing robots to better address user needs.

Muscle reoxygenation is slower after higher cycling intensity, and is faster and more reliable in locomotor than in accessory muscle sites.

Wearable near-infrared spectroscopy (NIRS) can be used during dynamic exercise to reflect the balance of muscle oxygen delivery and uptake. This study describes the behaviour and reliability of postexercise reoxygenation with NIRS as a function of exercise intensity at four muscle sites during an incremental cycling test. We discuss physiological components of faster and slower reoxygenation kinetics in the context of sport science and clinical applications. We hypothesised that reoxygenation would be slower at higher intensity, and that locomotor muscles would be faster than accessory muscles. We quantified test-retest reliability and agreement for each site. Twenty-one trained cyclists performed two trials of an incremental cycling protocol with 5-min work stages and 1-min rest between stages. NIRS was recorded from the locomotor vastus lateralis and rectus femoris muscles, and accessory lumbar paraspinal and lateral deltoid muscles. Reoxygenation time course was analysed as the half-recovery time (HRT) from the end of work to half of the peak reoxygenation amplitude during rest. Coefficient of variability (CV) between participants, standard error of the measurement (SEM) within participants, and intraclass correlation coefficient (ICC) for test-retest reliability were evaluated at 50%, 75%, and 100% peak workloads. A linear mixed-effects model was used to compare differences between workloads and muscle sites. HRT was slower with increasing workload in the VL, RF, and PS, but not DL. VL had the fastest reoxygenation (lowest HRT) across muscle sites at all workloads (HRT = 8, 12, 17s at 50%, 75%, 100% workload, respectively). VL also had the greatest reliability and agreement. HRT was sequentially slower between muscle sites in the order of VL < RF < PS < DL, and reliability was lower than for the VL. This study highlights the potential for using wearable NIRS on multiple muscle sites during exercise. Reoxygenation kinetics differ between local muscle sites with increasing intensity. Moderate-to-good reliability in the VL support its increasing use in sport science and clinical applications. Lower reliability in other muscle sites suggest they are not appropriate to be used alone, but may add information when combined to better reflect systemic intensity and fatigue during exercise at different intensities.

IS Intra-masseteric Dexamethasone Better than Intra-deltoid Injection in Reducing Post-operative Sequelae Following Impacted Third Molar Surgery?: A Randomized Clinical Study.

The post-operative sequelae of third molar surgical extractions need to be controlled in order to reduce patient morbidity. Dexamethasone is a well-researched drug which has established its merit as an anti-inflammatory agent. The aim of this randomized clinical study was to compare the patient-centric outcomes after pre-emptive intramuscular injection of dexamethasone into the masseter and deltoid, respectively. The outcomes measured were pain, facial swelling and mouth-opening postoperatively on Day 1, 3 and 7. The subjects were randomly divided into two groups. Group 1 received an intra-oral injection of 8mg of dexamethasone into the masseter muscle and a placebo injection of distilled-water into the deltoid muscle 2h before surgical removal of impacted mandibular third molar. Group 2 received an intra-oral placebo injection of distilled-water into masseter muscle and an 8mg injection of dexamethasone into deltoid muscle. On comparison, Group 1 patients experienced statistically significant less pain (VAS score on day 1, 3, and 7), facial swelling (day 1, 3), and restricted mouth-opening (day 1, 3). The study concluded that pre-emptive dexamethasone injection, at masseter or deltoid, is helpful in reducing post-operative sequelae of mandibular third molar extraction. However, the immediate post-operative outcomes were found to be better mitigated when the injection was administered locally into masseter muscle.

A Comparison of the Plyometric Performance of Upper Limbs between Experienced and Non-Experienced Athletes.

Although explosive upper-limb movements are far less studied than the equivalent lower-limb movements, they are important in many sports activities. The goal of this study was to explore, for the first time, the performance of street workout (SW) athletes who primarily focus on explosive and isometric strength in the upper limbs and to examine the effect of the contraction type on performance during a classical upper-body movement. Eighteen men took part in this study (age: 22.6 ± 2.1 years, height: 179.6 ± 7.1 cm, bodyweight: 71.9 ± 6.6 kg). Of these, nine practiced SW and nine practiced various team and individual sports-the latter serving as the control group. The athletes performed three different types of push-ups-one in a concentric way and two others in a plyometric way-and a fatigue-inducing push-up set. Jump heights, myoelectrical activities (through electromyography), muscle architecture, and hypertrophy (through ultrasonography) were measured. The results show no significant differences in jump height between the push-up types. Both groups confounded, but the SW athletes jumped on average 66 ± 21% higher than the control athletes (p < 0.05). There was no major difference in EMG between groups, regardless of the push-up type, but the SW athletes had a greater pectoralis major and anterior deltoid thickness as well as a greater pennation angle of the pectoralis major. The results suggest that the plyometric performance of the upper limbs does not follow the same pattern as that of the lower limbs. The SW group's greater capacity in performing explosive push-ups could be attributed to greater upper-body muscle hypertrophy and more efficient execution of the movement.

The Recommended Deltoid Intramuscular Injection Sites in the Adult Population: A Cadaveric Pilot Study With an Orthopedic Perspective.

Background and aim The deltoid is a common site for intramuscular injections, but guidelines for administration lack standardization. Global researchers propose various techniques, and recent study reports indicate a 1.5-15% incidence of nerve palsies due to injections. This pilot cadaveric study aimed to standardize the deltoid intramuscular injection sites in the Southeast Asian population. Methods This cadaveric study of a two-year duration was conducted in the Department of Anatomy as an intramural research project in collaboration with the Departments of Anatomy and Orthopedics. In the first year of study, which was the pilot phase of the project, the available six cadavers, i.e., 12 upper extremity specimens were dissected. Anthropometric measurements of deltoid muscle along with the distance of underlying neurovascular structures like the axillary nerve and posterior circumflex humeral artery were measured from neighboring bony landmarks. This article presents the observations of the six cadavers studied in the pilot phase and shall be followed up by another article after the project. Results In adults, in anatomical position, the mean distances of the axillary nerveand posterior circumflex humeral artery from the mid-acromial point are 8.19±0.616 and 8.66±0.968 cm, respectively. The deltoid thickness at 3, 5, and 7 cm from mid-acromial point was observed to be 1.079±0.13 cm (0.5-1.78 cm), 1.599±0.12 cm (1-2.96 cm), and 1.815±1.0 cm (1.2-2.5 cm), respectively. The acquired qualitative and quantitative data were tabulated, graphically represented, and statistically analyzed. Conclusions The deltoid intramuscular injection (IMI) must be given at or below the level of the midpoint of the deltoid muscle, but never in the upper half. We recommend a site, 4 fingerbreadths/9 cm below the mid-acromion point as the safest site to avoid injury to any underlying neurovascular structures.

Effect of electrical muscle stimulation on the improvement of deltoid muscle atrophy in a rat shoulder immobilization model.

Immobilization following trauma or surgery induces skeletal muscle atrophy, and improvement in the muscle atrophy is critical for successful clinical outcomes. The purpose of this study is to evaluate the effect of electrical muscle stimulation (EMS) on muscle atrophy. The study design is a controlled laboratory study. Eighty rats (56 to establish the deltoid muscle atrophy [DMA] model and 24 to evaluate the effect of EMS on the model) were used. DMA was induced by completely immobilizing the right shoulder of each rat by placing sutures between the scapula and humeral shaft, with the left shoulder as a control. After establishing the DMA model, rats were randomly assigned into three groups: low-frequency EMS (L-EMS, 10 Hz frequency), medium-frequency EMS (M-EMS, 50 Hz frequency), and control (eight rats per group). After 3 weeks, the deltoid muscles of each rat were harvested, alterations in gene expression and muscle cell size were evaluated, and immunohistochemical analysis was performed. DMA was most prominent 3 weeks after shoulder immobilization. Murf1 and Atrogin were significantly induced at the initial phase and gradually decreased at approximately 3 weeks; however, MyoD expressed an inverse relationship with Murf1 and Atrogin. IL6 expression was prominent at 1 week. The time point for the EMS effect evaluation was selected at 3 weeks, when the DMA was the most prominent with a change in relevant gene expression. The M-EMS group cell size was significantly larger than that of L-EMS and control group in both the immobilized and intact shoulders (all p < 0.05), without significant differences between the L-EMS and control groups. The M-EMS group showed significantly lower mRNA expressions of Murf1 and Atrogin and higher expressions of MyoD and Col1A1 than that of the control group (all p < 0.05). In immunohistochemical analysis, similar results were observed with lower Atrogin staining and higher MyoD and Col1A1 staining in the M-EMS group. DMA model was established by complete shoulder immobilization, with the most prominent muscle atrophy observed at 3 weeks. M-EMS improved DMA with changes in the expression of relevant genes. M-EMS might be a solution for strengthening atrophied skeletal muscles and facilitating rehabilitation after trauma or surgery.

Superior capsular reconstruction using the long head of biceps tendon: a biomechanical assessment of tenodesis location and angle of fixation

BackgroundMassive irreparable rotator cuff tears (MIRCT) treated with superior capsular reconstruction (SCR) using the long head of the biceps tendon have shown satisfactory early results. Different techniques and positions for biceps tenodesis have been described. This study aimed to evaluate the effect of tenodesis location and glenohumeral fixation angle for graft tensioning on the biomechanics of a SCR using a single strand biceps technique. MethodsEight cadaveric shoulders were mounted to a custom biomechanical simulator which employed static tone loads to the deltoid and rotator cuff muscles. All cadavers were first tested in the intact condition, and then in the simulated MIRCT condition by sectioning the tendinous insertions of the supraspinatus and upper border of the infraspinatus. SCR using the long head of the biceps tendon was then evaluated. Three biceps tenodesis locations relative to the greater tuberosity (anterior, middle, and posterior) and two glenohumeral fixation angles (0° and 30°) for graft tensioning were tested. An optical tracking system was used to quantify superior-inferior (SI) and anterior-posterior (AP) humeral head translation relative to the glenoid, while the functional abduction force was quantified using a load sensor. All tests were conducted at 0°, 30° and 60° of glenohumeral abduction in a randomized fashion. ResultsWhen assessing isolated superior humeral head migration, all biceps tenodesis locations were effective at decreasing superior migration, with no tenodesis location significantly better than the other (P=0.213). However, biceps grafts tensioned at 30° of glenohumeral abduction were significantly better at reducing proximal humeral migration as compared to graft tensioning at 0° abduction (P=0.008).Posterior humeral head translation observed in the MIRCT condition was significantly reduced when tensioning the biceps tendon at 30° of glenohumeral abduction compared to 0° for all tenodesis locations (P≤0.043). Tenodesis location also significantly influenced posterior humeral head translation (P=0.001), with middle and posterior positions restoring near normal humeral head position when fixed at 30° glenohumeral abduction. All SCR techniques using the biceps tendon improved the functional abduction force relative to the MIRCT condition, although no statistically significant differences were observed relative to the intact condition (P≥0.448). DiscussionSCR using the long head biceps tendon is biomechanically effective in reducing posterosuperior translation of the humeral head in the setting of a MIRCT. Graft tensioning and fixation at 30° of glenohumeral abduction combined with either a middle or posterior tenodesis location on the greater tuberosity most effectively restores near normal time-zero humeral head kinematics.

Preoperative Increases in T2-Weighted Fat-Suppressed Magnetic Resonance Imaging Signal Intensities Associated With Advanced Tissue Degeneration and Mitochondrial Dysfunction in Rotator Cuff Tears

PurposeThe purpose of this study was to investigate the relationship between magnetic resonance imaging (MRI) signal intensities and mitochondrial function in patients undergoing arthroscopic rotator cuff repair, assessed through histological and genetic profiling of tendon tissue. MethodsThis study, conducted between April 2022 and January 2023, included 20 patients undergoing rotator cuff repair for atraumatic/degenerative tears. Rotator cuff tendon edge samples were obtained during arthroscopic rotator cuff repair. Patients were classified based on signal intensity from preoperative T2-weighted fat suppressed MRI. Specifically, they were categorized as having either high or low signal intensity at the rotator cuff tendon edge, with the deltoid muscle serving as a reference. Comparative analyses specifically compared the histological features and genetic profiles of the tendon tissue at the rotator cuff tendon edge. Histological evaluation of harvested tendon specimens during arthroscopic rotator cuff repair employed the modified Bonar score. Real-time polymerase chain reaction was used to assess expression of various mitochondrial and apoptosis-related genes. The mitochondrial morphology of the rotator cuff torn site was examined using electron microscopy. ResultsThe higher signal intensity group showed significantly higher modified Bonar scores (p=0.0068), decreased mitochondrial gene expression, increased TUNEL-positive cells (p=0.032), lower SOD activity (p=0.011), reduced ATP5A (p=0.031), and increased cleaved caspase-9 activity (p=0.026) when compared to the lower signal intensity group. Electron microscopy revealed fewer mitochondrial cristae in the higher signal intensity group. ConclusionOur results suggest correlations between high MRI signal intensities and the presence of degeneration, mitochondrial dysfunction, and increased apoptosis in rotator cuff tissues. This underscores the utility of MRI signal intensity as an indicator of tissue condition. Clinical RelevanceBuilding on the established premise that elevated preoperative MRI signal intensities may indicate higher rates of postoperative rotator cuff re-tears, the current study substantiates these findings from a mitochondrial function perspective.

Biomechanical effects of deltoid muscle atrophy on rotator cuff tissue: a finite element study

The deltoid muscle and rotator cuff tissue are structural components that maintain the dynamic stability of the shoulder joint. However, atrophy of the deltoid muscle may affect the stability of the shoulder joint, which in turn alters the mechanical distribution of rotator cuff tissue. Currently, the effect of muscle volume changes in the deltoid muscle on reducing the load on the rotator cuff tissue is still unknown. Therefore, this paper intends to analyze the mechanical changes of rotator cuff tissue by deltoid muscle atrophy through finite elements. Based on previously published finite element shoulder models, the deltoid muscle was modeled by constructing deltoid muscle models with different degrees of atrophy as, 100% deltoid muscle (Group 1), 80% deltoid muscle (Group 2), and 50% deltoid muscle (Group 3), respectively. The three models were given the same external load to simulate glenohumeral joint abduction, and the stress changes in the rotator cuff tissue were analyzed and recorded. In all three models, the stress in the rotator cuff tissue showed different degrees of increase with the increase of abduction angle, especially in the supraspinatus muscle. At 90° of glenohumeral abduction, supraspinatus stress increased by 58% and 118% in Group 2 and Group 3, respectively, compared with Group 1; In the subscapularis, the stress in Group 3 increased by 59% and 25% compared with Group 1 and Group 2, respectively. In addition, the stress of the infraspinatus muscle and teres minor muscle in Group 2 and Group 3 were higher than that in Group 1 during the abduction angle from 30° to 90°. Deltoid atrophy alters the abduction movement pattern of the glenohumeral joint. During glenohumeral abduction activity, deltoid atrophy significantly increases the stress on the rotator cuff tissue, whereas normal deltoid volume helps maintain the mechanical balance of the rotator cuff tissue.

Effect of loupe and microscope on dentists’ neck and shoulder muscle workload during crown preparation

Although there is consensus among dentists that visual aids not only improve vision but also help improve posture, evidence is scarce. This study aimed to evaluate the effect of visual aids (loupe and microscope) on the muscle workload of dentists during crown preparation on dentiform first molars in each quadrant of a phantom head, considering dentists’ muscles, patients’ tooth positions and surfaces. Six right-handed dentists from a single tertiary hospital participated. Surface electromyography device recorded the muscle workload of the bilateral upper trapezius, sternocleidomastoid, cervical erector spinae, and anterior deltoid during crown preparation. The results showed significantly lower workload in all examined muscles when using a microscope compared to the naked eye (p < 0.05), whereas the loupe showed reduced workload in some specific muscles. The muscle with the highest workload for all visual aids was the cervical erector spinae, followed by the upper trapezius. When analyzed by tooth surface, while the loupe did not significantly reduce overall workload compared to the naked eye for each surface, the microscope significantly reduced workload for most surfaces (p < 0.05). Therefore, during crown preparation, the workload of the studied muscles can successfully be reduced with the use of a loupe or microscope.

Effect of electroacupuncture combined with rehabilitation techniques on shoulder function in patients with rotator cuff injuries.

The rotator cuff is located below the acromion and deltoid muscles and comprises multiple tendons that wrap around the humeral head, maintaining shoulder joint stability. To explore the effect of electroacupuncture combined with rehabilitation techniques on shoulder function in patients with rotator cuff injuries. We selected 97 patients with rotator cuff injuries treated in the People's Hospital of Yuhuan from February 2020 to May 2023. Patients were grouped using the envelope method. After treatment, the study group's treatment effective rate was 94.90% (46/49 patients), significantly higher than that in the control group (79.17%, 38/48 cases; P < 0.05). Before treatment, there was no difference in Constant Murley Score (CMS) scores, shoulder mobility, or 36-Item Short Form Health Survey (SF-36) scale scores (P > 0.05). Compared with those before treatment, the CMS scores (including pain, daily living ability, shoulder mobility, and muscle strength), all aspects of shoulder mobility (forward flexion, posterior extension, external rotation, internal rotation), and SF-36 scale scores (including physiological, psychological, emotional, physical, vitality, and health status) were higher in both groups after treatment and significantly higher in the study group (P < 0.05). There was no difference in the occurrence of complications between the two treatment groups (P > 0.05). Electroacupuncture combined with rehabilitation techniques has a good treatment effect on patients with rotator cuff injuries, helps accelerate the recovery of shoulder function, improves the quality of life, and is highly safe.

Safety and immunogenicity of the live-attenuated hRVFV-4s vaccine against Rift Valley fever in healthy adults: a dose-escalation, placebo-controlled, first-in-human, phase 1 randomised clinical trial

Rift Valley fever virus, a pathogen to ruminants, camelids, and humans, is an emerging mosquito-borne bunyavirus currently endemic to Africa and the Arabian Peninsula. Although animals are primarily infected via mosquito bites, humans mainly become infected following contact with infected tissues or fluids of infected animals. There is an urgent need for adequate countermeasures, especially for humans, because effective therapeutics or vaccines are not yet available. Here we assessed the safety, tolerability, and immunogenicity of a next-generation, four-segmented, live-attenuated vaccine candidate, referred to as hRVFV-4s, in humans. A first-in-human, single-centre, randomised, double-blind, placebo-controlled trial was done in Belgium in which a single dose of hRVFV-4s was administered to healthy volunteers aged 18-45 years. Participants were randomly assigned using an interactive web response system. The study population encompassed 75 participants naive to Rift Valley fever virus infection, divided over three dosage groups (cohorts) of 25 participants each. All participants were followed up until 6 months. Using a staggered dose escalating approach, 20 individuals of each cohort were injected in the deltoid muscle of the non-dominant arm with either 104 (low dose), 105 (medium dose), or 106 (high dose) of 50% tissue culture infectious dose of hRVFV-4s as based on animal data, and five individuals per cohort received formulation buffer as a placebo. Primary outcome measures in the intention-to-treat population were adverse events and tolerability. Secondary outcome measures were vaccine-induced viraemia, vaccine virus shedding, Rift Valley fever virus nucleocapsid antibody responses (with ELISA), and neutralising antibody titres. Furthermore, exploratory objectives included the assessment of cellular immune responses by ELISpot. The trial was registered with the EU Clinical Trials Register, 2022-501460-17-00. Between August and December, 2022, all 75 participants were vaccinated. No serious adverse events or vaccine-related severe adverse events were reported. Pain at the injection site (51 [85%] of 60 participants) was most frequently reported as solicited local adverse event, and headache (28 [47%] of 60) and fatigue (28 [47%] of 60) as solicited systemic adverse events in the active group. No vaccine virus RNA was detected in any of the blood, saliva, urine, or semen samples. Rift Valley fever virus nucleocapsid antibody responses were detected in most participants who were vaccinated with hRVFV-4s (43 [72%] of 60 on day 14) irrespective of the administered dose. In contrast, a clear dose-response relationship was observed for neutralising antibodies on day 28 with four (20%) of 20 participants responding in the low-dose group, 13 (65%) of 20 responding in the medium-dose group, and all participants (20 [100%] of 20) responding in the high-dose group. Consistent with the antibody responses, cellular immune responses against the nucleocapsid protein were detected in all dose groups, whereas a more dose-dependent response was observed for the Gn and Gc surface glycoproteins. Neutralising antibody titres declined over time, whereas nucleocapsid antibody responses remained relatively stable for at least 6 months. The hRVFV-4s vaccine showed a high safety profile and excellent tolerability across all tested dose regimens, eliciting robust immune responses, particularly with the high-dose administration. The findings strongly support further clinical development of this candidate vaccine for human use. The Coalition for Epidemic Preparedness Innovations with support from the EU Horizon 2020 programme.

Evaluation of the applicability of weak shoulder and arm sparing signs in amyotrophic lateral sclerosis by multiple neurologists and neurology residents: A single-center study.

Amyotrophic lateral sclerosis (ALS) exhibits selective muscle weakness. The weak shoulder and arm sparing signs, assessed by a single experienced neurologist, have been reported to be superior to previous signs in sensitivity and specificity. However, it is unknown whether the same results are observed when assessed by multiple neurologists. Subjects were retrospectively identified from our department's inpatient database from 2014 to 2023. Medical Research Council (MRC) scores of the deltoid (Del), biceps brachii (BB), triceps brachii (TB), and first dorsal interosseous (FDI) muscles were evaluated. The weak shoulder sign was defined as positive when Del was weaker than BB and TB. The arm sparing sign was defined as positive when both Del and FDI were weaker than BB and TB. Sensitivity was analyzed in all ALS patients and in subgroups based on the region of symptom onset, presence or absence of upper motor neuron (UMN) signs, and the Japanese ALS Severity Classification. Seventy-one patients with ALS were identified. Eight neurologists and three neurology residents evaluated each patient's MRC scores. The weak shoulder and arm sparing signs were observed in 72% and 48% of patients, respectively, with no significant difference in sensitivity across patient subgroups. The weak shoulder and arm sparing signs showed high and moderate sensitivity, respectively, consistent with a previous report, even when evaluated by multiple examiners. This expands the clinical utility and increases the reliability of these signs, potentially contributing to accurate ALS diagnosis when combined with other clinical features and objective assessments.

Muscle hypertrophy response across four muscles involved in the bench press exercise: Randomized 10 weeks training intervention

Background and purposeResistance training exercise provides increases in muscle size and is used by coaches and health care professional as a tool to improve functional performance. The aim of the present study was to investigate the effect of 10 weeks of resistance training program performed on the bench press (BP) exercise on the hypertrophic responses of four different muscles (pectoralis major, anterior and medial deltoid, brachii, and pectoralis minor) involved in the task compared to controls. MethodsTwenty-four healthy males were recruited, and thirteen performed a resistance training intervention while eleven were control. RT group trained for 10 weeks and the protocol consisted of a time under tension for each set of 36s (3–4 sets) with 12 repetitions with an intensity of 50–55% of the 1RM, a training frequency of 3 times a week, with a 3 min rest between sets. Muscle cross-sectional area (CSA) was measure by magnetic resonance imaging. ResultsIndividuals in the RT group demonstrated higher changes in CSA of the pectoralis major, pectoralis minor, anterior deltoid, and triceps brachii (P ≤ 0.019) than in the Control group. It was identified in the RT group higher increases in CSA of all muscles compared to medial deltoid (P ≤ 0.016), while pectoralis major demonstrated larger increases in CSA than pectoralis minor and triceps brachii (P ≤ 0.030). ConclusionsWe demonstrated that 10 weeks of resistance training performed on the BP exercise led to increases in muscle size of the muscles involved in the task, but not in the same magnitude.

Positional Analysis of Assisting Muscles for Handling-Assisted Exoskeletons.

In order to better design handling-assisted exoskeletons, it is necessary to analyze the biomechanics of human hand movements. In this study, Anybody Modeling System (AMS) simulation was used to analyze the movement state of muscles during human handling. Combined with surface electromyography (sEMG) experiments, specific analysis and verification were carried out to obtain the position of muscles that the human body needs to assist during handling. In this study, the simulation and experiment were carried out for the manual handling process. A treatment group and an experimental group were set up. This study found that the vastus medialis muscle, vastus lateralis muscle, latissimus dorsi muscle, trapezius muscle, deltoid muscle and triceps brachii muscle require more energy in the process of handling, and it is reasonable and effective to combine sEMG signals with the simulation of the musculoskeletal model to analyze the muscle condition of human movement.

Effects of the stretching program in male volleyball players with posterior shoulder tightness

BackgroundStretching programs are often used to improve muscle stiffness and thereby posterior shoulder tightness (PST); however, knowledge about their effects on the viscoelastic properties of muscles and performance is limited. ObjectiveThe aim of this study was to investigate the effects of a six-week stretching program on the viscoelastic properties of posterior shoulder muscles, shoulder functional performance and range of motion in volleyball players with PST. Study designA Randomized Controlled Trial. Level of evidenceLevel II. MethodsThe study was conducted in 34 male (aged 19–26) professional volleyball players with PST. They were randomly assigned to stretching and control groups. A stretching routine (combining sleeper stretch and cross body stretch exercises) was performed in the stretching group for six weeks. Measurements were taken during the first assessment and six weeks after the initiation of stretching for the following: shoulder external/internal rotation range of motion, spike velocity, single arm seated shot-put test, and infraspinatus– posterior deltoid muscle stiffness (by shear wave elastography). ResultsWhile the stretching group had statistically better results regarding increased shoulder internal rotation (p < 0.01), spike velocity (p = 0.02) and seated single arm shot put distance (p < 0.01), stretching did not have any effect on tissue stiffness. ConclusionsA 6-week program of sleeper stretch, and cross body stretch exercises improved shoulder internal rotation and functional performance. A clinically meaningful change in muscle mechanical properties cannot be detected after a 6-week stretching program.

Fatigue-related changes in intermuscular electromyographic coherence across rotator cuff and deltoid muscles in individuals with and without subacromial pain.

Neuromuscular fatigue induces superior migration of the humeral head in individuals with subacromial pain. This has been attributed to weakness of rotator cuff muscles and overactive deltoid muscles. Investigation of common inputs to motoneuron pools of the rotator cuff and deltoid muscles offers valuable insight into the underlying mechanisms of neuromuscular control deficits associated with subacromial pain. This study aims to investigate intermuscular coherence across the rotator cuff and deltoid muscles during a sustained submaximal isometric fatiguing contraction in individuals with and without subacromial pain. Twenty symptomatic and 18 asymptomatic young adults participated in this study. Surface electromyogram (EMG) was recorded from the middle deltoid (MD) and infraspinatus (IS). Intramuscular EMG was recorded with fine-wire electrodes in the supraspinatus (SS). Participants performed an isometric fatiguing contraction of 30° scaption at 25% maximum voluntary contraction (MVC) until endurance limit. Pooled coherence of muscle pairs (SS-IS, SS-MD, IS-MD) in the 2-5 Hz (delta), 5-15 Hz (alpha), and 15-35 Hz (beta) frequency bands during the initial and final 30 s of the fatigue task were compared. SS-IS and SS-MD delta-band coherence increased with fatigue in the asymptomatic group but not the symptomatic group. In the alpha and beta bands, SS-IS and SS-MD coherence increased with fatigue in both groups. IS-MD beta-band coherence was greater in the symptomatic than the asymptomatic group. Individuals with subacromial pain failed to increase common drive across rotator cuff and deltoid muscles and have altered control strategies during neuromuscular fatigue. This may contribute to glenohumeral joint instability and subacromial pain experienced by these individuals.NEW & NOTEWORTHY Through the computation of shared neural drive across glenohumeral muscles, this study reveals that individuals with subacromial pain were unable to increase shared neural drive within the rotator cuff and across the supraspinatus and deltoid muscles during neuromuscular fatigue induced by sustained isometric contraction. These deficits in common drive across the shoulder muscles likely contribute to the joint instability and pain experienced by these individuals.

Association between Deltoid Muscle Density and Proximal Humeral Fracture in Elderly Patients.

The potential role of deltoid muscle density in the occurrence of proximal humeral fractures remains uncertain. Therefore, the primary objective of this study was to examine the correlation between deltoid muscle density, as measured by CT attenuation value in Hounsfield units (HU), and the incidence of proximal humeral fractures in elderly patients. By investigating this association, we aim to shed light on the possible influence of deltoid muscle density on fracture risk in this specific population. A total of 68 patients with computed tomography (CT) images were retrospectively reviewed. Among them, 34 patients presented with fractures following low-energy injuries, while the remaining 34 patients served as controls and underwent CT scans after low-energy injuries without any fractures. The muscle density of the deltoid muscles was assessed at the approximate tubercle of humerus. We compared these parameters between the two groups and conducted analyses considering factors such as age, sex, laterality, and deltoid muscle density of the shoulders. The demographic factors related to the shoulder did not exhibit any significant association with proximal humeral fracture. However, we observed a noteworthy difference in deltoid muscle density between patients with fractures (40.85 ± 1.35) and the control group (47.08 ± 1.61) (p = 0.0042), indicating a lower muscle density in the fracture group. Based on the findings of this study, we can conclude that there exists a negative correlation between deltoid muscle density and the incidence of proximal humeral fractures. These results suggest that lower deltoid muscle density may be associated with an increased risk of proximal humeral fractures in the elderly population under investigation.