Deltoid Muscle Research Articles

Investigation of musculoskeletal symptoms, work postures, quantification of muscle activity, and estimation of grip/push forces among sonographers

AbstractDue to the physical nature of their work, sonographers are exposed to many musculoskeletal disorder risk factors, including awkward posture, repetitive movements, forceful manual exertion, and static muscle contractions, especially in the upper limbs. The current study is an investigation of musculoskeletal disorders among sonographers, caused by various occupational risk factors via different sonographic scan types. During the first phase of this study, the musculoskeletal symptoms and work postures of 29 subjects were investigated. During the second phase, muscle activity was quantified, and grip/push forces were estimated using the data obtained from 10 volunteer sonographers. 82% of sonographers experienced musculoskeletal symptoms. Based on the final scores and action levels obtained via rapid upper limb assessment, while performing scans of left regions; ergonomic changes and interventions were found necessary, to relieve stress on the sonographer's body. The results of muscular activity per muscle and scan type, showed that the mean muscle activity of the middle deltoid muscle was significantly higher during the right abdominal scan (17.64% maximum voluntary contraction [MVC]), compared to those of thyroid (12.54% MVC) and left abdominal (7.32% MVC) scans. Additionally, mean grip and push forces during both abdominal scans were significantly higher than those during the thyroid scan. Despite an injury risk during all scans, risk factor impact was different among scan types. This groundbreaking study represents the first that captures and measures both grip and push forces simultaneously, which may prove helpful while investigating corrective interventions or optimizing design of sonography robots and ergonomic probes in future studies.

Effects of victim's body posture and attacker's gender on slashing attacks: a biomechanical study.

Sharp force injury has been and will remain to be a major cause of violent death; however, scientific evaluations on the impact of body posture of the victim and gender of the perpetrator on sharp force injury have been scarce. The purpose of this study was to evaluate the biomechanical characteristics found in individuals (male and female) when using a Chinese kitchen knife to slash the neck of a dummy while it was in the standing and supine positions. This work offers a solid basis for forensic identifications, criminal investigations, and court trials. A total of 12 male and 12 female college students participated in this study. Kinematic, kinetic, and surface electromyography (sEMG) data were evaluated when slashing the neck of a dummy while it was in the standing and supine positions using a Chinese kitchen knife. When slashing the neck of a standing dummy, participants showed shorter contact time (19.5%) and slower shoulder velocities (30.9%) as well as higher hip velocity (26.0%) and increased root mean square (RMS) and integral electromyography (iEMG) for the anterior deltoid (51.3% and 51.2%, respectively) compared to those while the dummy was in the supine position (all p < 0.05), regardless of gender. When slashing a dummy's neck while it was in standing and supine positions, male participants showed higher shoulder, elbow, and wrist velocities (22.6%, 22.7%, and 24.4%, respectively) and higher slashing velocity (19.8%), slashing force (24.2%), and energy (46.2%) than female participants (all p < 0.05). In addition, male participants showed shorter contact time (17.8%), and the values of RMS and iEMG of the anterior deltoid, biceps brachii, extensor carpi radialis longus, and flexor carpi ulnaris were less than those of female participants (98.9%, 47.3%, 65.6%, and 33.4% for RMS and 115.1%, 59.4%, 80.1%, and 47.8% for iEMG, respectively). There was no difference in slashing speed, slashing force, and energy when using a Chinese kitchen knife to slash the dummy's neck while it was in different body postures (standing and supine), suggesting a similar level of injury severity. However, there were significant differences in slashing action patterns between the two body postures, with longer contact time, smaller hip velocity, greater shoulder velocity, and less muscle activation level of the deltoid exertion when slashing the dummy's neck in the supine position. Gender may have a greater effect on the severity of slashing, and the gender difference may be partly related to the body weight difference. The findings from this study may provide quantitative indicators and references for analyzing the motive behind the crime, as well as for case reconstruction, and for the court's conviction and sentencing processes.

Which muscle is the external rotation compensator after superior capsular reconstruction?

BackgroundSuperior capsular reconstruction (SCR) is a surgical option for massive irreparable rotator cuff tears, particularly involving the supraspinatus and infraspinatus. In this procedure, the torn infraspinatus is not repaired or reconstructed. However, an improvement in postoperative external rotation (ER) angle and strength is observed. There is a lack of studies explaining how ER is restored after SCR. The aim of this study is to identify the ER compensator by assessing the muscle volume of the posterior deltoid and teres minor. MethodsSixty-eight patients with massive rotator cuff tears underwent SCR during 2016-2021. Of these patients, 28 who met the following inclusion criteria were retrospectively reviewed: (1) massive rotator cuff tears including the supraspinatus and infraspinatus; (2) severe muscle atrophy and fatty change; (3) intact or reparable subscapularis tendon; (4) Hamada of grade 3 or lower. Posterior deltoid and teres minor volume were measured by using an open-source medical image processing software preoperatively and 1-year postoperatively. The percentage of the posterior deltoid and teres minor muscle volume change was compared between patients with 1-year postoperative ER manual motor testing (MMT) of grade 5 and of grade < 5. The relationship between grade of fatty change, percentage of the muscle volume change, and ER angle and strength were evaluated. ResultsThere was a significant increase in the 1-year postoperative teres minor volume compared with the preoperative volume (24.6±10.3 cm³ versus 20.9±8.3 cm³, p<0.000), while the posterior deltoid volume remained unchanged (178.1±48.3 cm³ versus 178.8±47 cm³). Patients with ER MMT of grade 5 had a greater teres minor volume compared to those with an ER MMT grade of less than 5 (22.3% versus 9.4%), although this difference was not significant (p=0.074, 95% CI=-1.3–27.0). The posterior deltoid volume showed no significant change. The percentage of teres minor volume change had a weak positive correlation with ER strength (r=0.308, p=0.055, 95% CI=-0.02–1.0). There was a significant negative correlation between ER strength and the severity of both preoperative and postoperative fatty changes in the teres minor (r=-0.258, p=0.065, 95% CI=-1.0–-0.042 and r=-0.323, p=0.028, 95% CI=-1.0–-0.113, respectively). The pre- and postoperative fatty changes in the teres minor were negatively correlated with the percentage of teres minor volume change (r=-0.298, p=0.062, 95% CI=-1.0–0.031 and r=-0.413, p=0.015, 95% CI=-1.0–-0.1, respectively). ConclusionThe teres minor may serve as a potential compensator for ER in patients with massive rotator cuff tears following SCR.

Intraoperative Electromyogram Analysis of Postural Musculature With Three-dimensional Screen Display Versus Operating Microscope in Ophthalmic Surgery: A Clinical Methods Study

Background and Objective: To objectively analyze the effect of three-dimensional screen-based surgery (3D SBS) versus traditional operating microscope (TOM) on operating surgeon posterior chain postural musculature during ophthalmic surgery. We hypothesized an increase in median amplitude of electromyography (EMG) signals when using a TOM compared to 3D SBS. The goal was to assess surgical ergonomics that may contribute to cervical and lumbar spine pathology. EMG analysis was conducted at the University of Cincinnati Medical Center Epilepsy Monitoring Unit. Data were collected in the private practice setting at Cincinnati Eye Institute. Materials and Methods: This was an institutional review board exempt, nonrandomized, prospective, single center, n = 1 clinical methods study. EMG surface electrodes were affixed to the bilateral splenius capitis, sternocleidomastoid, upper trapezius, anterior deltoid, and quadratus lumborum musculature. EMG data were collected across four sessions consisting of one day each using 3D SBS or a TOM, and two cross-over days. A survey regarding surgeon comfort was administered before, during, and after each surgery, and at the end of each day. Results: EMG cross-over data demonstrated an increase in muscle activation in all measured muscles except the anterior deltoids and right quadratus lumborum with use of a TOM. Survey data showed increased fatigue when using a TOM relative to 3D SBS. Conclusion: EMG demonstrated increased postural muscle activation when utilizing TOM relative to 3D SBS. Similar to previous studies, our survey data suggest inferior ergonomics of TOM relative to 3D SBS. [ Ophthalmic Surg Lasers Imaging Retina 2024;55:XX–XX.]

Utility of the Repetitive Nerve Stimulation Test and Needle EMG in the Trapezius Muscle for the Early Diagnosis of ALS.

To document the utility of decremental responses in the repetitive nerve stimulation test (RNS) and spontaneous activities in needle electromyography (EMG) in the trapezius muscle for the diagnosis of amyotrophic lateral sclerosis. Subjects were retrospectively identified from our EMG database. Cervical spondylosis was represented as a disease control group. We investigated the sensitivity and specificity of RNS and EMG in the trapezius muscle and those of diagnostic criteria including the Gold Coast criteria (GCC). We reviewed 120 patients with amyotrophic lateral sclerosis and 17 patients with cervical spondylosis. "RNS or EMG" achieved the highest sensitivity (85%). The specificity was the highest for RNS (94%). Addition of RNS of the deltoid muscle achieved 98% sensitivity in the upper-limb onset amyotrophic lateral sclerosis. The sensitivity of the GCC was very high (88%). Neurophysiological parameters investigated in this study having close to 100% specificities or sensitivities are useful as complements to the GCC.

Insights into the Medial Pectoral Nerve Transfer for Shoulder Abduction in Brachial Plexus Injuries: A Retrospective Case Series Analysis

Treatment priority in C5, C6, and C7 brachial plexus root avulsion is the recovery of shoulder function through reinnervation of shoulder muscles. The medial pectoral nerve is a potential donor for axillary nerve transfer, but outcomes are sparsely reported. This study reports the results of medial pectoral nerve transfer to the axillary nerve. We conducted a retrospective analysis of 12 patients with traumatic brachial plexus injury (C5, C6, and C7 root avulsion) who underwent medial pectoral nerve transfer to the axillary nerve. Sociodemographic and clinical characteristics, including electromyography findings, were documented. We assessed postoperative shoulder abduction strength and range of motion. Statistical analyses compared presurgery and postsurgery outcomes and contrasted our results with those from a study using spinal accessory nerve transfer to the suprascapular nerve. Postsurgery, the mean shoulder abduction range of motion was 65.45°, with a median strength of M2. Significant improvement was noted compared to preoperative values. However, outcomes did not significantly surpass those from spinal accessory nerve transfer. Electromyography showed a low incidence of motor unit action potentials in the deltoid. Medial pectoral nerve transfer to the axillary nerve did not yield superior results in shoulder abduction and deltoid reinnervation in our group of patients. At present, different nerve donors may also need to be considered for deltoid muscle reinnervation in patients with C5, C6, and C7 root avulsion to achieve better shoulder abduction recovery.

Comparing Access to Engaging Hill-Sachs Lesions Between the Modified Posterior Deltoid Split Approach and Standard Deltopectoral Approach for Bone Grafting.

Hill-Sachs lesions are common after shoulder instability, and treatment options vary but include remplissage or implantation of structural bone graft. Large Hill-Sachs lesions not addressed by remplissage are challenging to manage and may frequently require an open surgical approach for bone filling treatment options. The optimal approach to maximize visualization of the humeral head during these procedures remains unclear. The purpose of this study was to compare the area of the humeral head accessed using a modified posterior deltoid split approach versus a standard deltopectoral approach without surgical dislocation, with particular attention to access of engaging Hill-Sachs lesions for the purpose of bone grafting in the setting of anterior shoulder instability. It was hypothesized that both approaches would provide equal access to a simulated Hill-Sachs lesion. Controlled laboratory study. Four human cadaveric shoulders were mounted in the beach-chair position. The modified posterior deltoid split approach and nonextensile deltopectoral approaches were performed. A typical Hill-Sachs lesion was simulated on the humeri. The percentage of the total surface area of the humeral head that was accessed, including access to the simulated Hill-Sachs lesion, was mapped using 3-dimensional digitizing software. The deltopectoral approach provided 45% ± 15.2% access (range, 24% to 58%) to the humeral head versus 22.2% ± 6.1% (range, 17% to 30%) for the modified posterior deltoid split approach (P = .057). The modified posterior deltoid split approach enabled 100% access of the simulated Hill-Sachs lesion compared with 0% for the nonextensile deltopectoral approach. The angle of access to the articular surface was direct and perpendicular with the modified posterior deltoid split approach. The overall surface area of the humeral head accessed via the modified posterior deltoid split approach was less compared with the deltopectoral approach; however, the entire area of a typical Hill-Sachs lesion was able to be accessed from the modified posterior deltoid split approach, whereas this area was not well visualized from the standard deltopectoral approach. The modified posterior deltoid split approach provided sufficient access to the humeral head for the purposes of grafting an engaging Hill-Sachs lesion in the setting of anterior shoulder instability.

Analysis of Muscles Electrical Activities During Bench Press

The primary objective of the study was to compare the muscle electrical activity during Benchpress for the different muscle groups. The amount of contribution of each mentioned muscle duringbench press was also analyzed.For the purpose of the present investigation, total of 10 male power lifterswere chosen as the sample forthe study.The analysis showed that there is a significant difference in the muscle electrical activity during Benchpress for the different muscle groups. The results pertaining to EMG data of 1RM bench pressrevealed maximum muscle electrical activity in case of Pectoralis Major. Hence the Pectoralis Majordisplayed better muscle electrical activity than the Anterior deltoid and Triceps

Comparative analysis of biomechanical characteristics between the new Tai Chi elastic band exercise for opening and closing movement and elastic band resistance training for the reverse fly movement.

The objective of this study was to compare and analyze the representative opening and closing movement of Tai Chi elastic band exercise with the reverse fly movement of elastic band resistance training. The aim was to explore the biomechanical differences between the two exercises and provide theoretical support for the application of Tai Chi elastic band exercise in health intervention. A total of 26 male participants were recruited and randomly divided into two groups in a 1:1 ratio. There were 13 participants in each Tai Chi elastic band exercise group and elastic band resistance training group. Both groups of participants used an elastic band to perform movement in the experiment. Experimental data were collected using the Vicon infrared motion capture system and Delsys surface EMG system. The AnyBody software was utilized to simulate the creation of a musculoskeletal model for both exercises. The study found that the Tai Chi elastic band exercise group exhibited smaller horizontal abduction angle and flexion angle of the shoulder joint, as well as normalized RMS of the anterior deltoid and triceps brachii, compared to the elastic band resistance training group (P < 0.01); the Tai Chi elastic band exercise group exhibited greater elbow flexion angle, elbow flexion torque, and muscle strength of the infraspinatus, coracobrachialis, biceps brachii, brachialis and brachioradialis, compared to the elastic band resistance training group (P < 0.01); the Tai Chi elastic band exercise group exhibited smaller horizontal abduction angular velocity of the shoulder joint and a lower normalized RMS of the posterior deltoid, compared to the elastic band resistance training group (P < 0.05). (1) The opening and closing movement of Tai Chi elastic band exercise is characterized by a large elbow flexion angle, a small shoulder joint horizontal angle and flexion angle, and a slow and uniform speed of movement. The reverse fly movement of elastic band resistance training is characterized by a large horizontal abduction angle of the shoulder joint, a large flexion angle of the shoulder joint, a small flexion angle of the elbow joint, and a fast and uneven speed. (2) The opening and closing movement exerts a greater torque on the elbow flexion, while the reverse fly movement exerts a greater torque on the shoulder joint horizontal abduction and external rotation. (3) The opening and closing movement provide greater stimulation to the infraspinatus, coracobrachialis, and elbow flexor, while the reverse fly movement provides greater stimulation to the posterior deltoid, anterior deltoid, subscapularis, and elbow extensor. In summary, the variation in joint angle, joint angular velocity, and hand position could be the factor contributing to the differences in joint torque and muscle activity between the opening and closing movement of Tai Chi elastic band exercise and the reverse fly movement of elastic band resistance training.

Activation patterns of rotator-cuff muscles from quantitative IVIM DWI after physical testing

BackgroundThe diagnostic value of clinical rotator cuff (RC) tests is controversial, with only sparse evidence available about their anatomical specificity. We prospectively assessed regional RC muscle activation patterns by means of intravoxel incoherent motion (IVIM) diffusion-weighted magnetic resonance imaging (MRI) after the execution of common clinical RC tests.MethodsTen healthy subjects (five males, five females) underwent three sessions of diffusion-weighted 3-T shoulder MRI before and after testing the supraspinatus (SSP, Jobe test, session 1), subscapularis (SSC, lift-off test, session 2, at least 1 week later), and infraspinatus muscle (ISP, external rotation test, session 3, another week later). IVIM parameters (perfusion fraction, f; pseudo-diffusion coefficient. D*; and their product, fD*) were measured in regions of interest placed in images of the SSP, SSC, ISP, and deltoid muscle. The Wilcoxon signed-rank test was used for group comparisons; p-values were adjusted using the Bonferroni correction.ResultsAfter all tests, fD* was significantly increased in the respective target muscles (SSP, SSC, or ISP; p ≤ 0.001). After SSP testing, an additional significant increase of fD* was observed in the deltoid, the SSC, and the ISP muscle (p < 0.001). After the SSC and ISP tests, no significant concomitant increase of any parameter was observed in the other RC muscles.ConclusionIVIM revealed varying activation patterns of RC muscles for different clinical RC tests. For SSP testing, coactivation of the deltoid and other RC muscles was observed, implying limited anatomical specificity, while the tests for the SSC and ISP specifically activated their respective target muscle.Relevance statementFollowing clinical RC tests, IVIM MRI revealed that SSP testing led to shoulder muscle coactivation, while the SSC and ISP tests specifically activated the target muscles.Key PointsIn this study, intravoxel incoherent motion MRI depicted muscle activation following clinical rotator cuff tests.After supraspinatus testing, coactivation of surrounding shoulder girdle muscles was observed.Subscapularis and infraspinatus tests exhibited isolated activation of their respective target muscles.Graphical

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.