A Game-Based Rehabilitation System for Upper-Limb Cerebral Palsy: A Feasibility Study

Game-based rehabilitation systems provide an effective tool to engage cerebral palsy patients in physical exercises within an exciting and entertaining environment. A crucial factor to ensure the effectiveness of game-based rehabilitation systems is to assess the correctness of the movements performed by the patient during the game-playing sessions. In this study, we propose a game-based rehabilitation system for upper-limb cerebral palsy that includes three game-based exercises and a computerized assessment method. The game-based exercises aim to engage the participant in shoulder flexion, shoulder horizontal abduction/adduction, and shoulder adduction physical exercises that target the right arm. Human interaction with the game-based rehabilitation system is achieved using a Kinect sensor that tracks the skeleton joints of the participant. The computerized assessment method aims to assess the correctness of the right arm movements during each game-playing session by analyzing the tracking data acquired by the Kinect sensor. To evaluate the performance of the computerized assessment method, two groups of participants volunteered to participate in the game-based exercises. The first group included six cerebral palsy children and the second group included twenty typically developing subjects. For every participant, the computerized assessment method was employed to assess the correctness of the right arm movements in each game-playing session and these computer-based assessments were compared with matching gold standard evaluations provided by an experienced physiotherapist. The results reported in this study suggest the feasibility of employing the computerized assessment method to evaluate the correctness of the right arm movements during the game-playing sessions.

Multivariate analysis of body morphometric traits in conjunction with performance of reproduction and milk traits in crossbred progeny of Murrah × Jafarabadi buffalo (Bubalus bubalis) in North-Eastern Brazil

We studied the relationship between body morphometric traits, and their underlying association with milk production (MP), lactation length (LL), first calving interval (FCI) and subsequent calving interval (CI) of crossbred progeny of Murrah × Jafarabadi buffalo aiming to assist in selection programs. We carried out principal component analysis (PCA) of the body morphometric traits, which include breast width (BW), thigh width (THW), hip width (HW), rump width (RW), rump length (RL), body depth (BD), body length (BL), height withers (HEW), rear height (RH), shoulder width (SW), thorax width (TW), loin width (LW), distance from the head to ischium (DHI), and thoracic perimeter (TP). We determined the association of morphometric traits with milk/reproduction traits using canonical correlation analysis (CCA). The analysis revealed that the first six PCA accounted for 82.14% of the total observed variation, and the traits THW, HW, TW, LW, RW, HEW, TP, RH, and BW, accounted for almost half (48.00%) of the total variance indicating a higher contribution in body structural conformation. The first canonical function was significant (p<0.05), accounted for 72.46% of the total variance, and the canonical correlation was 0.56, indicating the dependence between both groups of traits. Higher canonical loadings were obtained for LL (0.49), FCI (0.46), BW (-0.71), BL (-0.56), DHI (-0.34), HEW, (-0.38) and TP (-0.50). These traits were most important for the derivation of canonical statistical variables, and presented a higher canonical correlations (r) between the dependent (LL/FCI) and independent (BW, BL, DHI, HEW and TP) groups. The results could suggest that the body morphometric traits THW, HW, TW, LW, RW, HEW, BD, TP, RH, and BW could play important role in body structural composition, indicating a suitable functional type, and aid designing of selection programs for buffalo breeding.

Quantifying the Multidimensional Impedance of the Shoulder During Volitional Contractions

The neuromuscular control of the shoulder requires regulation of 3D joint mechanics, but it is unknown how these mechanics vary during tasks that load the shoulder in different directions. The purpose of this study was to quantify how the 3D mechanics of the shoulder change with voluntary torque production. Eleven participants produced voluntary isometric torques in one of six directions along three measurement axes. Impedance was estimated by applying small, pseudorandom angular perturbations about the shoulder as participants maintained steady state torques. The nonparametric impedance frequency response functions estimated from the data were parameterized by a collection of second-order linear systems to model the 3D inertia, viscosity, and stiffness of the shoulder. Each component of the 3D stiffness matrix scaled linearly with volitional torque production. Viscosity also increased monotonically with torque but nonlinearly. The directions of maximal stiffness and viscosity were consistently aligned towards the direction of torque production. Further, the shoulder was least stiff and least viscous in the direction of internal/external rotation, suggesting it may be more prone to injury along this axis. These experimental findings and the corresponding mathematical model summarizing our results provide novel insights into how the neuromuscular system regulates 3D shoulder mechanics in response to volitional muscle activations.

The effects of target location on musculoskeletal load, task performance, and subjective discomfort during virtual reality interactions

The objective of this study was to evaluate the effect of different target locations on musculoskeletal loading and task performance during virtual reality (VR) interactions. A repeated-measures laboratory study with 20 participants (24.2 ± 1.5 years; 10 males) was conducted to compare biomechanical exposures (joint angle, moment, and muscle activity in the neck and shoulder), subjective discomfort, and task performance (speed and accuracy) during two VR tasks (omni-directional pointing and painting tasks) among different vertical target locations (ranged from 15° above to 30° below eye height). The results showed that neck flexion/extension angle and moment, shoulder flexion angle and moment, shoulder abduction angle, muscle activities of neck and shoulder muscles, and subjective discomfort in the neck and shoulder significantly varied by target locations (p's < 0.001). The target locations at 15° above and 30° below eye height demonstrated greater shoulder flexion (up to 52°), neck flexion moment (up to 2.7Nm), anterior deltoid muscle activity, and subjective discomfort in the neck and shoulder as compared to the other locations. This result indicates that excessive vertical target locations should be avoided to reduce musculoskeletal discomfort and injury risks during VR interactions. Based on relatively lower biomechanical exposures and trade-off between neck and shoulder postures, vertical target location between eye height and 15° below eye height could be recommended for VR use.

Characterizing the comfort limits of forces applied to the shoulders, thigh and shank to inform exosuit design

Recent literature emphasizes the importance of comfort in the design of exosuits and other assistive devices that physically augment humans; however, there is little quantitative data to aid designers in determining what level of force makes users uncomfortable. To help close this knowledge gap, we characterized human comfort limits when applying forces to the shoulders, thigh and shank. Our objectives were: (i) characterize the comfort limits for multiple healthy participants, (ii) characterize comfort limits across days, and (iii) determine if comfort limits change when forces are applied at higher vs. lower rates. We performed an experiment (N = 10) to quantify maximum tolerable force pulling down on the shoulders, and axially along the thigh and shank; we termed this force the comfort limit. We applied a series of forces of increasing magnitude, using a robotic actuator, to soft sleeves around their thigh and shank, and to a harness on their shoulders. Participants were instructed to press an off-switch, immediately removing the force, when they felt uncomfortable such that they did not want to feel a higher level of force. On average, participants exhibited comfort limits of ~0.9–1.3 times body weight on each segment: 621±245 N (shoulders), 867±296 N (thigh), 702±220 N (shank), which were above force levels applied by exosuits in prior literature. However, individual participant comfort limits varied greatly (~250–1200 N). Average comfort limits increased over multiple days (p<3e-5), as users habituated, from ~550–700 N on the first day to ~650–950 N on the fourth. Specifically, comfort limits increased 20%, 35% and 22% for the shoulders, thigh and shank, respectively. Finally, participants generally tolerated higher force when it was applied more rapidly. These results provide initial benchmarks for exosuit designers and end-users, and pave the way for exploring comfort limits over larger time scales, within larger samples and in different populations.

Healing Rate and Clinical Outcomes of Lesser Tuberosity Osteotomy for Anatomic Shoulder Arthroplasty

Several techniques are available for subscapularis management during total shoulder arthroplasty (TSA). Lesser tuberosity osteotomy (LTO) is advocated owing to improved biomechanical strength and high rates of healing. However, displacement or nonunion of the LTO could theoretically cause functional deficits for the affected shoulder. The purpose of this study is to examine the healing rate and clinical outcomes of LTO in patients undergoing anatomic TSA.

Methods

A retrospective review of our institution's prospectively enrolled TSA registry was performed. Patients undergoing primary TSA who had an LTO performed and radiographs at a minimum of 3 months postoperatively were included. Two fellowship-trained shoulder and elbow surgeons reviewed all radiographs and categorized LTO healing into three groups: healed, nondisplaced nonunion, or displaced nonunion. Physical examination data and patient-reported outcome scores including American Shoulder and Elbow Score, Single Assessment Numeric Evaluation scores, and the Veteran Rand mental and physical component scores were obtained at a median of 1 year after surgery. Comparative statistical analysis was performed on the healed versus nondisplaced nonunion groups.

Results

We included 142 shoulders in 130 patients who met the inclusion criteria with an average age of 65.2 years (SD: 10.3). Radiographic evaluation at a median of 1.0 years postoperatively (range: 6 months to 2.2 years) revealed 124 (87%) healed LTO, 12 (8%) nondisplaced nonunions, and six (5%) displaced nonunions. The median American Shoulder and Elbow Score total score was 89.2 (IQR: 72.2, 98.3) in the healed LTO group versus 96.7 (30, 98.3) in the LTO nondisplaced nonunion group (P = 0.9637). The median Veteran Rand mental component was 55.1 (IQR: 43.4, 61.0) in the healed LTO group versus 54.6 (38.8, 58.2) in the LTO nondisplaced nonunion group (P = 0.5679). The median Single Assessment Numeric Evaluation score was 85.0 (IQR: 70.0, 95.0) in the LTO-healed group versus 75.1 (35.0, 97.1) in the LTO nondisplaced nonunion group (P = 0.7699). There were no significant differences in revision surgery occurrence between the groups to address subscapularis instability: one patient in the LTO-healed group underwent revision surgery for subscapularis repair 3 months after primary surgery because of continued pain and weakness, and no patients in the other LTO groups underwent revision surgery.

Conclusion

Although there is a risk of nonunion and displacement using the LTO technique in TSA, the overall clinical outcomes and radiographic union rates are high with a very low risk of revision surgery. In addition, radiographic evidence of nonunion does not significantly correlate with clinical outcomes.

Comparative biomechanical characteristics of one-arm hang in climbing for beginners and qualified athletes

PURPOSE

The aim of the study was to identify the basic kinematic characteristics of the one-arm hang in climbing for beginners and qualified climbers.

MATERIAL AND METHODS

Technique of the one-arm hang in climbing among 20 leading climbers of the World and Ukraine and 20 beginner male amateur climbers was analyzed. A qualified athlete participated in the demonstration of various models of the one-arm hang performance. By means of Kinovea software 0.8.15, the kinematic characteristics of two models of the technique were analyzed (model 1 for beginner athletes, model 2 for qualified athletes).

RESULTS

The presence of significant differences ( p < 0.001) between beginners and qualified athletes in the magnitude of the angles between the shoulder and clavicle, between the spine and the vertical axis in the phase of fixation of the one-arm hang was revealed. The dynamics of the angle between the shoulder and clavicle from the moment of capture of the climbing hold to the phase of fixation of the hang was shown. A theoretical justification for the correct climbing technique regarding to the laws of mechanics and the laws of force interaction in kinematic chain was provided.

CONCLUSIONS

Beginner athletes carry out the one-arm hang mainly due to the ligamentous apparatus of the joints of the shoulder girdle with minimal inclusion of muscles, which is dangerous by trauma to the ligaments of the shoulder joint. Skilled athletes perform the one-arm hang with trunk and leg muscles included, which reduces the strain from the ligamentous apparatus and lowers the possibility of injury to the ligaments of the shoulder joint.

Effects of different fatigue locations on upper body kinematics and inter-joint coordination in a repetitive pointing task

Studies have shown that muscle fatigue can lead to posture, joint angle, inter-joint coordination and variability alterations. However, the three-dimensional kinematic effects of localized muscular fatigue on a multijoint movement remain unclear. Healthy young adults (N = 17, 10 females) performed a standing repetitive pointing task when they were non-fatigued, and after localized muscle fatigue was induced at the elbow, the shoulder, and the trunk using isometric protocols performed until exhaustion. Joint angles and angular standard deviation (SD) of trunk, shoulder and elbow, and continuous relative phase (CRP) and CRP SD between trunk and shoulder, and shoulder and elbow were computed and compared between fatigue conditions. Results showed that trunk lateral flexion SD increased after fatigue of the elbow (0.1°, p = 0.04), shoulder (0.1°, p = 0.04) and trunk (0.1°, p<0.01). However, fatigue at different muscles brought different kinematic changes. Shoulder fatigue induced the greatest overall changes, with angular changes at all three joints. Trunk fatigue increased the shoulder horizontal abduction SD, elbow flexion SD and trunk-shoulder CRP. Elbow fatigue induced angular changes at trunk, shoulder and elbow, but did not affect CRP or CRP SD. This study highlights the crucial role of trunk variability in compensating for localized muscle fatigue during a repetitive upper limb task performed while standing.

In-Water and On-Land Swimmers' Symmetry and Force Production

Although performance and biomechanical evaluations are becoming more swimming-specific, dryland testing permits monitoring of a larger number of performance-related variables. However, as the degree of comparability of measurements conducted in-water and on land conditions is unclear, we aimed to assess the differences between force production in these two different conditions. Twelve elite swimmers performed a 30 s tethered swimming test and four isokinetic tests (shoulder and knee extension at 90 and 300°/s) to assess peak force, peak and average torque, and power symmetry index. We observed contralateral symmetry in all the tests performed, e.g., for 30 s tethered swimming and peak torque shoulder extension at 90°/s: 178 ± 50 vs. 183 ± 56 N (p = 0.38) and 95 ± 37 vs. 94 ± 35 N × m (p = 0.52). Moderate to very large direct relationships were evident between dryland testing and swimming force production (r = 0.62 to 0.96; p < 0.05). Swimmers maintained similar symmetry index values independently of the testing conditions (r = −0.06 to −0.41 and 0.04 to 0.44; p = 0.18–0.88). Asymmetries in water seems to be more related to technical constraints than muscular imbalances, but swimmers that displayed higher propulsive forces were the ones with greater force values on land. Thus, tethered swimming and isokinetic evaluations are useful for assessing muscular imbalances regarding propulsive force production and technical asymmetries.

The Relationship between General Upper-Body Strength and Pole Force Measurements, and Their Predictive Power Regarding Double Poling Sprint Performance

In recent years, there is an increasing importance of double poling (DP) performance regarding the outcome in classic cross-country skiing (XCS) races. So far, different approaches were used to predict DP performance but there is a lack of knowledge how general strength parameters are related to DP performance parameters gathered from in field-test situations. Therefore, the aim of this study was to determine the relationship between general strength measurements of different upper-body segments and pole force measurements during a DP sprint exercise. In addition, multiple linear regressions were calculated to determine the predictive power of theses variables regarding DP sprint performance, represented as maximum velocity. Thirteen none-elite cross-country skiers performed two 60 m DP sprints at maximal speed on a tartan track using roller skis. In addition, maximum isometric and concentric strength tests were performed on a motor-driven dynamometer with four major upper-body segments (trunk flexion / extension, shoulder / elbow extension). Especially the mean pole force and the strength test parameters correlated significantly (r ≥ 0.615) in all except one comparison. However, regression analyses revealed that neither pole force parameters (R² = 0.495) nor isometric (R² = 0.456) or dynamic (R² = 0.596) strength test parameters could predict the DP performance significantly. This study showed that standardized isokinetic strength tests could be used to estimate pole force capabilities of XCS athletes. However, pole-force and strength test parameters failed to predict significantly maximal velocity during a DP sprint exercise, which might be attributed to the non-elite subject group.

Effect of different trunk postures on scapular muscle activities and kinematics during shoulder external rotation

BACKGROUND

Shoulder external rotation at abduction (ER) is a notable motion in overhead sports because it could cause strong stress to the elbow and shoulder joint. However, no study has comprehensively investigated the effect of different trunk postures during ER. This study aimed to investigate the effect of different trunk postures on scapular kinematics and muscle activities during ER.

METHODS

Fourteen healthy men performed active shoulder external rotation at 90° of abduction with the dominant arm in 15 trunk postures. At maximum shoulder external rotation in 15 trunk postures, including 4 flexion-extension, 6 trunk rotation, and 4 trunk side-bending postures, as well as upright posture as a control, scapular muscle activities and kinematics were recorded using surface electromyography and an electromagnetic tracking device, respectively. The data obtained in the flexion-extension, trunk rotation, and trunk side-bending postures were compared with those obtained in the upright posture.

RESULTS

In the flexion-extension condition, scapular posterior tilt and external rotation significantly decreased, but the muscle activities of the lower trapezius and infraspinatus significantly increased in maximum trunk flexion. Moreover, scapular upward rotation and the activity of the serratus anterior significantly increased in maximum trunk extension. In the rotation condition, scapular posterior tilt and external rotation significantly decreased, but the activity of the serratus anterior significantly increased in the maximum contralateral trunk rotation posture. In the trunk side-bending condition, scapular posterior tilt and the external rotation angle significantly decreased.

CONCLUSION

Trunk postures affected scapular kinematics and muscle activities during ER. Our results suggest that different trunk postures activate the lower trapezius and serratus anterior, which induce scapular posterior tilt.

Biomechanical and Metabolic Effectiveness of an Industrial Exoskeleton for Overhead Work

Overhead work activities can lead to shoulder pain and serious musculoskeletal disorders (WMSD), such as rotator cuff injury and degeneration. Recently developed exoskeletons show promising results in supporting workers in such activities. In this study, a novel exoskeleton was investigated for two different overhead tasks with twelve participants. To investigate the effects of the device, electromyographic (EMG) signals of different shoulder and adjacent muscles as well as kinematic and metabolic parameters were analyzed with and without the exoskeleton. The mean EMG amplitude of all evaluated muscles was significantly reduced when the exoskeleton was used for the overhead tasks. This was accompanied by a reduction in both heart rate and oxygen rate. The kinematic analysis revealed small changes in the joint positions during the tasks. This study demonstrated the biomechanical and metabolic benefits of an exoskeleton designed to support overhead work activities. The results suggest improved physiological conditions and an unloading effect on the shoulder joint and muscles which are promising indicators that the exoskeleton may be a good solution to reduce shoulder WMSD among workers who carry out overhead tasks on a regular basis.

Synergies reciprocally relate end-effector and joint-angles in rhythmic pointing movements

During rhythmic pointing movements, degrees of freedom (DOF) in the human action system-such as joint-angles in the arm-are assumed to covary to stabilise end-effector movement, e.g. index finger. In this paper, it is suggested that the end-effector movement and the coordination of DOF are reciprocally related in synergies that link DOF so as to produce the end-effector movement. The coordination of DOF in synergies and the relation between end-effector movement and DOF coordination received little attention, though essential to understand the principles of synergy formation. Therefore, the current study assessed how the end-effector movement related to the coordination of joint-angles during rhythmic pointing across target widths and distances. Results demonstrated that joint-angles were linked in different synergies when end-effector movements differed across conditions. Furthermore, in every condition, three joint-angles (shoulder plane of elevation, shoulder inward-outward rotation, elbow flexion-extension) largely drove the end-effector, and all joint-angles contributed to covariation that stabilised the end-effector. Together, results demonstrated synergies that produced the end-effector movement, constrained joint-angles so that they covaried to stabilise the end-effector, and differed when end-effector movement differed. Hence, end-effector and joint-angles were reciprocally related in synergies-indicating that the action system was organised as a complex dynamical system.

A Systematic Methodology to Analyze the Impact of Hand-Rim Wheelchair Propulsion on the Upper Limb

Manual wheelchair propulsion results in physical demand of the upper limb extremities that, because of its repetitive nature, can lead to chronic pathologies on spinal cord injury patients. The aim of this study was to design and test a methodology to compare kinematic and kinetic variables of the upper limb joints when propelling different wheelchairs. Moreover, this methodology was used to analyze the differences that may exist between paraplegic and tetraplegic patients when propelling two different wheelchairs. Five adults with paraplegia and five adults with tetraplegia performed several propulsion tests. Participants propelled two different wheelchairs for three minutes at 0.833 m/s (3 km/h) with one minute break between the tests. Kinematic and kinetic variables of the upper limb as well as variables with respect to the propulsion style were recorded. Important differences in the kinetic and kinematic variables of the joints of the upper limb were found when comparing paraplegic and tetraplegic patients. Nevertheless, this difference depends on the wheelchair used. As expected, in all tests, the shoulder shows to be the most impacted joint.

Sex differences in glenohumeral muscle activation and coactivation during a box lifting task

Manual material handling is associated with shoulder musculoskeletal disorders, especially for women. Sex differences in glenohumeral muscle activity may contribute to women's higher injury risk by affecting shoulder load and stability. We assessed the effects of sex (25 women vs 26 men) and lifting load (6 kg vs 12 kg) on muscle activation during box lifting from hip to eye level. Surface and intramuscular electromyography were recorded from 10 glenohumeral muscles. Most muscles were more activated for the heavier box and for women. These effects were larger for 'prime movers' than for stabilisers and antagonists. Despite their apparently heterogeneous effects on muscle activity, sex and mass did not affect Muscle Focus, a metric of coactivation. This may be partly related to the limited sensitivity of the Muscle Focus. Nevertheless, sex differences in strength, more than in coactivation patterns, may contribute to the sex imbalance in the prevalence of musculoskeletal disorders. Practitioner summary: We studied sex differences in glenohumeral muscle activity in a lifting task to eye level. Women lifting a 6-kg box activated their muscles similarly to men lifting a 12-kg box, i.e. up to 48% of their maximum capacity. Interventions minimising shoulder load should be implemented, especially for women. Abbreviations: BB: biceps brachii; DeltA: anterior deltoid; DeltL: lateral deltoid; DeltP: posterior deltoid; DoF: degrees of freedom; ED: effect duration; EMG: electromyography; ES: effect size; Infra: infraspinatus; Lat: latissimus dorsi; MF: muscle focus; MMH: manual material handling; MVA: maximal voluntary activation; Pect: pectoralis major; Subscap: subscapularis; Supra: supraspinatus; TB: triceps brachii.

Age and sex-related upper body performance differences in competitive young tennis players

Objective

The aims of this study were to analyze the shoulder functional profile of young male and female tennis players and to establish the relationship among physical variables and serve speed.

Methods

A total of 128 Spanish tennis players (Under-13 (n = 32/32 males/females) and Under-15 (n = 36/28 males/females), were tested during National training camps. Tests included passive shoulder range of motion (ROM) for both internal (IR) and external rotation (ER) and isometric strength (i.e., IR and ER) of the dominant/non-dominant shoulders, medicine ball throws (MBT), and serve speed. Age and sex pairwise comparisons were carried using the Hedges’ g index (d_g).

Results

Results showed age and sex effects on serve speed and all MBT, with males showing greater changes (1.51≤d_g≤1.98) with age than females (0.92≤d_g≤1.35; p<0.05). U15 males showed higher (p<0.05) absolute shoulder IR and ER strength than U13, with only significant differences between males and females in the U15. Regarding ROM, U15 males showed a decreased IR ROM compared to U13 (d_g = -0.84; p<0.05) and higher significant IR bilateral deficit (d_g = 0.51; p<0.05). The distances obtained in the different MBT were the variables more correlated to serve speed.

Conclusion

The present results suggest that shoulder strength, medicine ball throws and serve speed increased along with age in young elite tennis players of both sexes. However, a decreased range of motion and bilateral deficit for glenohumeral internal rotation is evident in male under-15 tennis players. Muscle strength, power and shoulder range of motion are key factors for serve speed in young tennis players.

Postural and muscular adaptations to repetitive simulated work

Complex repetitive tasks are common in the workplace and have been associated with upper extremity disorders. The purpose of this study was to examine the progressive effects of highly repetitive work on joint kinematics and muscle activity of the trunk and upper extremity. Fifteen healthy men performed 60 one-minute cycles of 4 simulated automotive-related tasks. Electromyography of eight muscles and kinematics of the trunk and right upper extremity were collected. Data were analysed at 12-min intervals and divided into a complete work cycle. The time to complete the work cycle decreased by 6.3 s over the trials. Peak shoulder flexion decreased and peak elbow flexion increased during the work cycle. Muscle activity magnitude and variability was influenced by time during the repetitive tasks. This study found adaptations to highly repetitive but light work in only 1 h; redistributing muscle demands within the shoulder over time may reduce muscle fatigue development. Practitioner Summary: While the work was not strenuous, we were able to demonstrate muscular and postural adaptations in a single hour of simulated work. By evaluating both the whole work cycle and the sub-tasks, we aim to develop new methods for evaluating the risk of complex tasks in prolonged repetitive work.

Outcomes of the lower trapezius muscle activities during various narrow-base push-up exercises

BACKGROUND

In clinics, training of the lower trapezius muscle for the rehabilitation of the shoulder is often applied. The narrow-base push-up exercise is considered suitable training of the proximal shoulder complex, but the effect on the lower trapezius muscle has not yet been investigated.

OBJECTIVE

The purpose of this study was to investigate the effect of push-up, push-up plus, and support surfaces on the lower trapezius muscle during the narrow-base push-up exercise.

METHODS

A total of 11 males participated in this study. Surface electromyographic response of the lower trapezius muscle was examined during the narrow-base push-up exercise.

RESULTS

The lower trapezius muscle activity increased significantly in both the stable and the unstable conditions during the narrow-base push-up phase compared with both conditions during the narrow-base push-up plus phase.

CONCLUSIONS

The narrow-base push-up is considered a suitable exercise for strengthening the lower trapezius muscle regardless of support surfaces.

Validity and reliability of serratus anterior hand held dynamometry

BACKGROUND

Strength testing of the serratus anterior muscle with hand held dynamometry (HDD) in supine subjects has low reproducibility, and is influenced by compensatory activity of other muscles like the pectoralis major and upper trapezius. Previously, two manual maximum voluntary isometric contraction tests of the serratus anterior muscle were reported that recruited optimal surface electromyography (sEMG) activity in a sitting position. We adapted three manual muscle tests to make them suitable for HHD and investigated their validity and reliability.

METHODS

Twenty-one healthy adults were examined by two assessors in one supine and two seated positions. Each test was repeated twice. Construct validity was determined by evaluating force production (assessed with HHD) in relation to sEMG of the serratus anterior, upper trapezius and pectoralis major muscles, comparing the three test positions. Intra- and interrater reliability were determined by calculating intra-class correlation coefficients (ICC) smallest detectable change (SDC) and standard error of measurement (SEM).

RESULTS

Serratus anterior muscle sEMG activity was most isolated in a seated position with the humerus in 90° anteflexion in the scapular plane. This resulted in the lowest measured force levels in this position with a mean force of 296 N (SEM 15.8 N). Intrarater reliability yielded an ICC of 0.658 (95% CI 0.325; 0.846) and an interrater reliability of 0.277 (95% CI -0.089;0.605). SDC was 127 Newton, SEM 45.8 Newton.

CONCLUSION

The results indicate that validity for strength testing of the serratus anterior muscle is optimal with subjects in a seated position and the shoulder flexed at 90° in the scapular plane. Intrarater reliability is moderate and interrater reliability of this procedure is poor. However the high SDC values make it difficult to use the measurement in repeated measurements.

On the edge between soft and rigid: an assistive shoulder exoskeleton with hyper-redundant kinematics

In this paper, we present a prototype of an innovative portable shoulder exoskeleton for human assistance and augmentation. The device provides torques to flexion/extension movements of the shoulder, compensating for gravitational forces, and is passively compliant along the remaining degrees of freedom letting the shoulder moving along them. The novelty of our system is a flexible link, made of a hyper-redundant passive structure, that avoids joint misalignment by adapting to the complex movements of the humerus head, similarly to a soft component. The flexible link is compliant to rotations around one axis but rigid around the other two axes, allowing transmission of flexion/extension torque but kinematically transparent along the remaining degrees of freedom. The device is light weight and allows to cover around the 82% of the shoulder flexion/extension range of motion. The exoskeleton was tested on a cohort of 5 healthy subjects, monitoring shoulder kinematics, interaction forces and acquiring the electromyography of three major muscles contributing to shoulder flexion. During both static postures and dynamic movements, assistance from the exoskeleton resulted in a significant reduction of muscular effort in the anterior (-32.2% in static, -25.3% in dynamic) and medial deltoid (56.9% in static, -49.6% in dynamic) and an average reduction of the biceps brachii.

IMU-based assistance modulation in upper limb soft wearable exosuits

Soft exosuits have advantages over their rigid counterparts in terms of portability, transparency and ergonomics. Our previous work has shown that a soft, fabric-based exosuit, actuated by an electric motor and a Bowden cable, reduced the muscular effort of the user when flexing the elbow. This previous exosuit used a gravity compensation algorithm with the assumption that the shoulder was adducted at the trunk. In this investigation, the shoulder elevation angle was incorporated into the gravity compensation control via inertial measurement units (IMUs). We assessed our updated gravity compensation model with four healthy, male subjects (age: $26.2 \pm 1.19$ years) who followed an elbow flexion reference trajectory which reached three amplitudes $(25^{\circ}, 50^{\circ}, 75^{\circ})$ and was repeated at three shoulder angles $(25^{\circ}, 50^{\circ}, 75^{\circ})$. To assess the performance of the exosuit; the smoothness, tracking accuracy and muscle activity were investigated during each motion. We found a reduction of biceps brachii activation (24.3%) in the powered condition compared to the unpowered condition. In addition, there was an improvement in kinematic smoothness (0.83%) and a reduction of tracking accuracy (26.5%) in the powered condition with respect to the unpowered condition. We can conclude that the updated gravity compensation algorithm has increased the number of supported movements by considering the shoulder elevation, which has improved the usability of the device.

Absolute reliability and concurrent validity of a novel electromechanical pulley dynamometer for measuring shoulder rotation isometric strength in asymptomatic subjects. Study conducted at Pontificia Universidad Católica, Santiago, Chile

OBJECTIVE

To estimate the test-retest reliability of measurements in shoulder internal and external rotators' isometric peak torque using a new dynamometer, and to compare it with isokinetic dynamometer.

METHODS

The validity study was conducted in September-October 2016 at Pontificia Universidad Catolica de Chile and the Clinica Las Condes, Santiago, Chile. It comprised of asymptomatic university students who were randomly tested twice within a two-week period while in a supine position at 90° of shoulder abduction, using the novel functional electromechanical pulley dynamometer. Concurrent validity was assessed through comparing the values with the gold standard isokinetic dynamometer in the same position. SPSS 17 was used for data analysis.

RESULTS

Of the 24 subjects, 5(21%) were males and 19(79%) were females. The overall mean age was 23.1±2.2 years, body mass index 23.6±2.13 kg/m2 and Shoulder Pain and Disability Index score was 3.9±6.4. There was no statistically non-significant difference in terms of test-retest trials and between the devices (p>0.05). Absolute reliability was 24.3% for internal rotation and 27.9% for external rotation. Both dynamometer systems were very highly correlated for internal rotators peak torque (0.93) and highly correlated for external rotators peak torque (0.84).

CONCLUSIONS

Compared to the gold standard, the new device was found to be a valid instrument in measuring maximal voluntary isometric peak torque in internal and external rotation.

Evaluation and comparison of lift styles for an ideal lift among individuals with different levels of training

Training for safe lifting techniques is used by employers to lower their workers' exposure to risk of workplace injuries. To determine effectiveness of training, 266 attendees at two professional conferences were asked to identify and demonstrate their preferred lift technique with the demonstration being an ideal floor-to-waist height lift of a10-kg weighted crate. 'Bend your knees' was the most frequent preferred cue for each of the self-reported participant groups: untrained (n = 65), trained (n = 86), and trainers (n = 115) according to safe lifting techniques. The demonstrations showed that this cue was incorporated into the skill of lifting by all groups. Trained participants showed a stronger conformity for depth of squat; but, the overall variability suggested a lack of consensus on the ideal depth of squat. The trained group experienced less loading at L5/S1 (p = .021) compared to untrained that was countered by higher loading of the knee (p = .046). Trainers showed lower knee (p = .006) and shoulder (p = .03) loading with similar L5/S1 loading as the trained participants suggesting a broader set of criteria for safe lifting. While the study population was likely biased towards a common understanding of safe lifting techniques given the conferences were for ergonomists and safety professionals, the results provided valuable insight into potential knowledge gaps, and key messaging that is being delivered and integrated into one's knowledge; a program review of lift training is recommended.

Evaluation of a proposed chair with an arm support for wiring terminal blocks on a vertical plane

To reduce the muscular exertion of an operator wiring terminal blocks on a vertical plane, a chair with a unique back that can be used as a back support or arm support is proposed in this study. A digital version of the chair was first developed based on anthropometric data and tested with a digital anthropometric subject using the Jack software before the physical chair was developed. To evaluate the effects of the physical chair, an experiment of wiring terminal blocks was conducted with 12 subjects to test whether the use of the arm support can reduce muscular exertion. The results showed that (1) exertion on the anterior deltoid, upper trapezium, and erector spinae muscles decreased with decrease in terminal block height; (2) using the arm support reduced exertion on the anterior deltoid and upper trapezium muscles; and (3) the subjects reported less self-perceived fatigue in the wrist, elbow, and shoulder regions when the arm support was used. These results confirm that the proposed chair can reduce muscular workload in the shoulder muscle over a proper range of working heights. However, using the arm support may restrict certain working postures and lead to force generation in upper extremity muscles.

Using EMG Amplitude and Frequency to Calculate a Multimuscle Fatigue Score and Evaluate Global Shoulder Fatigue

OBJECTIVE

The authors developed a function to quantify fatigue in multiple shoulder muscles by generating a single score using relative changes in EMG amplitude and frequency over time.

BACKGROUND

Evaluating both frequency and amplitude components of the electromyographic signal provides a more complete evaluation of muscle fatigue than either variable alone; however, little effort has been made to combine time and frequency domains for the evaluation of myoelectric fatigue.

METHOD

Surface EMG was measured from 14 shoulder muscles while participants performed simulated, repetitive work tasks until exhaustion. Each 60-s work cycle consisted of four tasks (dynamic push, dynamic pull, static drill, static force target matching task) scaled to participants' anthropometrics and strength. The function was generated to calculate a multimuscle fatigue score (MMFS) based on changes in EMG frequency, amplitude, and the number of muscles showing signs of myoelectric fatigue (increase in EMG amplitude; decrease in EMG frequency).

RESULTS

The function was evaluated through changes in MMFS over time: first (31.8 ± 14.6), middle (47.6 ± 25.3), last (58.6 ± 35.5) reference exertions ( p < .05). The evaluation of the relationships between MMFS and changes in strength ( r = -0.510) and MMFS and perceived fatigue (RPF) ( r = 0.298) showed significant relationships over time ( p < .05). MMFS scores increased over time ( p < .05) with significant relationships between MMFS and strength changes and RPF ( p < .05).

CONCLUSION AND APPLICATION

The MMFS allows for comparisons between workplace tasks, which can aid in workplace design to mitigate the development of fatigue.