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It is unknown how structural (sex, stature, body mass) and functional (strength, flexibility) personal factors influence lifting strategy in paramedic work. We explored whether variance in peak low back forces and kinematic coordination patterns could be explained by structural and functional personal factors in paramedic lifting tasks. Seventy-two participants performed backboard and stretcher lifts. Peak low back forces normalised to body mass, as well as kinematic coordination patterns, were calculated as dependent variables. Being female, stronger, shorter, having higher body mass, and/or having greater lower body range of motion (ROM) were all independently associated with lower normalised low back forces across backboard and stretcher lifting. Females and stronger individuals seemed to define a movement objective to consistently minimise compressive forces, while individuals with greater hip ROM consistently minimised anteroposterior shear forces. The efficacy of improving strength and hip ROM to reduce low back forces in paramedic lifting should be investigated. Practitioner summary: Females, stronger individuals, and individuals with greater hip range of motion consistently exhibited lower normalised low back forces in paramedic lifting. Improving strength and hip range of motion via training is a potential proactive ergonomics approach to reduce peak low back forces in paramedic lifting tasks. [ABSTRACT FROM AUTHOR]

Markerless motion capture has been made available by the development of pose estimation algorithms that provide both an estimate of the location of body keypoints in two-dimensional images and its associated confidence. It seems relevant to use this additional information for three-dimensional (3D) point reconstruction. Yet, it has been little described, nor has its influence on 3D point reconstruction. Eight participants performed a manual material handling task, which was recorded by 10 video cameras. Each video was processed using OpenPose. Different 3D point reconstruction methods were compared: direct linear transform (DLT) and weighted DLT (wDLT), with 10 cameras and with a subset of 4 cameras. For each keypoint, confidence and position deviation from the 3D reconstructed point with 10 cameras projected in the image reference frame were assessed. Results suggest that using confidence information reduces both average and maximum 3D distance between 3D points reconstructed with 4 and 10 cameras. [ABSTRACT FROM AUTHOR]

There are no reports in the literature of powerlifting success after amputation. We had the unique opportunity to characterize functional outcomes, strength, muscle contractility and size, and corticospinal excitability in an accomplished, competitive powerlifter (best competition squat = 205.0 kg, deadlift = 262.7 kg) with a unilateral, transtibial amputation relative to amputee controls. Four men (age range = 23-49 years) with unilateral, lower-limb amputation (3 transtibial, 1 transfemoral) participated in 1 laboratory visit. We assessed 10-m gait speed, the timed up and go (TUG) test, 5-time sit-to-stand performance (5TSTS), contractile properties of the vastus lateralis (VL) and medial gastrocnemius by tensiomyography, and VL cross-sectional area (CSA) by ultrasonography. Unilateral assessments for the intact limb included isokinetic knee extension and flexion torque and power and transcranial magnetic stimulation derived corticospinal excitability. An interview with the powerlifter provided contextual perspective. Compared with the control subjects, the powerlifter performed the 5TSTS faster (6.8%), exhibited faster VL contraction times (intact limb = 12.2%; residual limb = 23.9%), and showed larger VL CSA for the intact limb (46.7%). The powerlifter exhibited greater knee extension and flexion peak torque and mean power, particularly at 180°·s -1, as well as greater corticospinal excitability for the intact VL (65.6%) and tibialis anterior (79.6%). By contrast, the control subjects were faster in the TUG (18.3%) and comfortable (13.0%) and fast (21.4%) in the 10-m walk test. The major themes of our interview included needing to modify lifting mechanics, persistence, and remarkable pain tolerance. Our findings highlight the impressive neuromuscular adaptations that are attainable after lower-limb amputation. [ABSTRACT FROM AUTHOR]

Back exosuits deliver mechanical assistance to reduce the risk of back injury, however, minimising restriction is critical for adoption. We developed the adaptive impedance controller to minimise restriction while maintaining assistance by modulating impedance based on the user's movement direction and nonlinear sine curves. The objective of this study was to compare active assistance, delivered by a back exosuit via our adaptive impedance controller, to three levels of assistance from passive elastics. Fifteen participants completed five experimental blocks (4 exosuits and 1 no-suit) consisting of a maximum flexion and a constrained lifting task. While a higher stiffness elastic reduced back extensor muscle activity by 13%, it restricted maximum range of motion (RoM) by 13°. The adaptive impedance approach did not restrict RoM while reducing back extensor muscle activity by 15%, when lifting. This study highlights an adaptive impedance approach might improve usability by circumventing the assistance-restriction trade-off inherent to passive approaches. Practitioner summary: This study demonstrates a soft active exosuit that delivers assistance with an adaptive impedance approach can provide reductions in overall back muscle activity without the impacts of restricted range of motion or perception of restriction and discomfort. [ABSTRACT FROM AUTHOR]

Resistance training intensity is commonly quantified as the load lifted relative to an individual's maximal dynamic strength. This approach, known as percent-based training, necessitates evaluating the one-repetition maximum (1RM) for the core exercises incorporated in a resistance training program. However, a major limitation of rigid percent-based training lies in the demanding nature of directly testing the 1RM from technical, physical, and psychological perspectives. A potential solution that has gained popularity in the last two decades to facilitate the implementation of percent-based training involves the estimation of the 1RM by recording the lifting velocity against submaximal loads. This review examines the three main methods for prescribing relative loads (%1RM) based on lifting velocity monitoring: (i) velocity zones, (ii) generalized load-velocity relationships, and (iii) individualized load-velocity relationships. The article concludes by discussing a number of factors that should be considered for simplifying the testing procedures while maintaining the accuracy of individualized L-V relationships to predict the 1RM and establish the resultant individualized %1RM-velocity relationship: (i) exercise selection, (ii) type of velocity variable, (iii) regression model, (iv) number of loads, (v) location of experimental points on the load-velocity relationship, (vi) minimal velocity threshold, (vii) provision of velocity feedback, and (viii) velocity monitoring device. [ABSTRACT FROM AUTHOR]

Objective: To explore (1) the goodness of fit of generalized and individualized relationships between the maximum number of repetitions performed to failure (RTF) and the fastest mean velocity and peak velocity of the sets (RTF–velocity relationships), (2) the between-sessions reliability of mean velocity and peak velocity values associated with different RTFs, and (3) whether the errors in the prediction of the RTF under fatigued and nonfatigued conditions differ between generalized and individualized RTF–velocity relationships. Methods: Twenty-three sport-science students performed 4 testing sessions with the prone bench pull exercise in a Smith machine: a 1-repetition-maximum [1RM] session, 2 identical sessions consisting of singles sets of RTF against 4 randomized loads (60%–70%–80%–90%1RM), and 1 session consisting of 4 sets of RTF against the 75%1RM. Results: Individualized RTF–velocity relationships presented a higher goodness of fit (r2 =.96–.97 vs.67–.70) and accuracy (absolute errors = 2.1–2.9 repetitions vs 2.8–4.3 repetitions) in the prediction of the RTF than generalized RTF–velocity relationships. The reliability of the velocity values associated with different RTFs was generally high (average within-subject coefficient of variation = 4.01% for mean velocity and 3.98% for peak velocity). The error in the prediction of the RTF increased by ~1 repetition under fatigue (ie, set 1 vs sets 2–4). Conclusions: Individualized RTF–velocity relationships can be used with acceptable precision and reliability to prescribe the loads associated with a given RTF during the match a specific XRM during the prone bench pull exercise, but a lower accuracy is expected in a fatigued state. [ABSTRACT FROM AUTHOR]

The aim of this study was to assess whether lifting velocity (MV) can provide accurate estimations of the maximum number of repetitions that can be performed to failure (RTF) during the parallel back‐squat exercise performed in a Smith machine. Thirty male wrestlers from the Turkey Olympic preparation center (age = 22.6 ± 2.2 years) completed four testing sessions: a session to determine the back‐squat one‐repetition maximum [1RM], two sessions consisting of single sets to failure against three loads (90%‐80%‐70%1RM), and one session consisting of four sets to failure against the 75%1RM. The goodness‐of‐fit of the generalized RTF‐MV relationship was strong (r2 = 0.838), but the individualized RTF‐MV relationships were stronger (r2 = 0.957 ± 0.058). Only 3 out of 60 individualized RTF‐MV relationships revealed a r2 lower than the r2 of the generalized RTF‐MV relationship (r2 = 0.685, 0.779 and 0.810). The reliability of the fastest MV associated with each RTF ranged from acceptable (4 out of 15 RTFs) to high (11 out of 15 RTFs). The raw and absolute errors in the prediction of RTF did not increase under fatigue and were comparable for both generalized (raw errors: −1.0–0.3 repetitions; absolute errors: 1.1–1.7 repetitions) and individualized (raw errors: −0.8 to 0.1 repetitions; absolute errors: 1.2–1.8 repetitions) RTF‐MV relationships. These results indicate that RTF can be predicted with acceptable precision from MV recordings in resistance‐trained skilled wrestlers during the parallel back‐squat exercise performed in a Smith machine. Highlights: The maximum number of repetitions completed to failure (RTF) can be predicted with acceptable precision from mean velocity (MV) recordings in resistance‐trained skilled wrestlers during the parallel back‐squat exercise performed in a Smith machine.The raw and absolute errors in the prediction of RTF is not influenced by the fatigue levels experienced at the beginning of the set.For more accurate RTF‐MV relationships, familiarity with lifting at maximal intended velocity and performing sets to failure seems beneficial. [ABSTRACT FROM AUTHOR]

Soft back exoskeletons are aimed at reducing musculoskeletal effort during manual handling tasks, contributing to the prevention of low back disorders like lumbar strains and sprains or intervertebral disk problems. However, large differences in their biomechanical effects are observed in the literature. A possible explanation could be the lack or disparity of familiarization protocols with the exoskeleton. The aim of this experimental study was to characterize the familiarization process with a soft back-support occupational exoskeleton and determine the time needed to stabilize biomechanical variables. Participants carried out 6 familiarization sessions of 1 h to the CORFOR® soft back-exoskeleton. Joint kinematics, postural stability, exoskeleton pressure perception, muscle activity, and performance were measured at the beginning of the first session and at the end of each session during stoop and squat liftings. Results showed that back kinematics, performance, and exoskeleton pressure perception changed during the first sessions and stabilized after sessions 3 or 4, depending on the variable. The authors recommend a familiarization protocol for the CORFOR® soft back-exoskeleton of 4 sessions of 1 h duration. This recommendation could help CORFOR® users, for instance, in the automotive industry, the food retail industry, or the agriculture field. [ABSTRACT FROM AUTHOR]

This study aimed to establish an ambulatory field-friendly system based on miniaturised wireless flexible sensors for studying the biomechanics of human-exoskeleton interactions. Twelve healthy adults performed symmetric lifting with and without a passive low-back exoskeleton, while their movements were tracked using both a flexible sensor system and a conventional motion capture (MoCap) system synchronously. Novel algorithms were developed to convert the raw acceleration, gyroscope, and biopotential signals from the flexible sensors into kinematic and dynamic measures. Results showed that these measures were highly correlated with those obtained from the MoCap system and discerned the effects of the exoskeleton, including increased peak lumbar flexion, decreased peak hip flexion, and decreased lumbar flexion moment and back muscle activities. The study demonstrated the promise of an integrated flexible sensor-based system for biomechanics and ergonomics field studies as well as the efficacy of exoskeleton in relieving the low-back stress associated with manual lifting. This study established and tested a flexible sensor-based ambulatory system for biomechanical evaluation of human-exoskeleton interactions and as a promising new tool for field ergonomics studies in practical or naturalistic settings. Abbreviations: MoCap: motion capture; WMSD: Work-related musculoskeletal disorders; EMG: electromyography; IMU: inertial measurement unit; TES: thoracic erector spinae; LES: lumbar erector spinae; WITH: tasks performed with wearing the exoskeleton; WITHOUT: tasks performed without wearing the exoskeleton; RMS: root mean square; RMSE: root-mean-square error; r: Pearson's correlation coefficient; ASIS: anterior superior iliac spine [ABSTRACT FROM AUTHOR]

BACKGROUND: Lifting heavy objects can induce postural stress and low back pain. OBJECTIVE: This study aimed to examine the effect of object weight expectations on trunk muscle activity and assess trunk muscle activity in people with chronic low back pain. METHODS: Twenty-two male college students (11 healthy and 11 participants with chronic low back pain) were recruited. The procedure was performed in three settings: lifting an expected 5-kg object, lifting an unexpected 10-kg object, and lifting an expected 10-kg object. Lifting was divided into five phases, and the muscle activity in each phase was compared between groups (chronic low back pain/control), object weight predictions, and phases. RESULTS: Compared to the control group, the chronic low back pain group had higher erector spinae muscle activity, regardless of weight or prediction, and significantly higher rectus femoris muscle activity in the early lifting phase of the expected 10-kg object (p = 0.043). Compared to when lifting the expected 10-kg object, erector spinae muscle activity was higher in the early lifting phase of the control group when lifting the unexpected 10-kg object (p = 0.016). CONCLUSIONS: Healthy individuals and individuals with chronic low back pain had different recruitment strategies for lifting objects heavier than predicted. [ABSTRACT FROM AUTHOR]

BACKGROUND: Work-related low back pain (LBP) increases the workforce disability and healthcare costs. This study evaluated the LBD risk level associated with handling the ACGIH TLVs in lifting tasks corresponding to various horizontal and vertical zones. OBJECTIVE: The aim of this study was to compare the low-risk ACGIH TLV to risk outcomes from various validated lifting assessment methods, including the OSU LBD Risk Model, NIOSH Lifting Equation, and LiFFT. METHODS: Twenty-four subjects were recruited for this study to perform various lifting conditions. The various ergonomic assessment methods were then used to obtain the risk assessment outcomes. RESULTS: The selected assessment methods showed that the ACGIH-defined TLVs are associated with less than high-risk for LBD for all the assessed tasks. The findings showed a moderate agreement (Kendall's W = 0.477) among the various assessment methods risk outcomes. The highest correlation (ρ= 0.886) was observed between the NIOSH Lifting Equation and LiFFT methods risk assessment outcomes. CONCLUSION: The findings showed that ACGIH-defined TLVs possesses less than high-risk for LBD. The outcomes of the selected ergonomic assessment methods moderately agree to each other. [ABSTRACT FROM AUTHOR]

Augmented tactile and performance feedback has been used to (re)train a modified lifting technique to reduce lumbar spine flexion, which has been associated with low back disorder development during occupational repetitive lifting tasks. However, it remains unknown if the presence of trunk extensor neuromuscular fatigue influences learning of this modified lifting technique. Therefore, we compared the effectiveness of using augmented tactile and performance feedback to reduce lumbar spine flexion during a repetitive lifting task, in both unfatigued and fatigued states. Participants completed repetitive lifting tests immediately before and after training, and 1-week later, with half of the participants completing training after fatiguing their trunk extensor muscles. Both groups demonstrated learning of the modified lifting technique as demonstrated by increased thorax-pelvis coordination variability and reduced lumbar range of motion variability; however, experiencing trunk extensor neuromuscular fatigue during lift (re)training may have slight negative influences on learning the modified lifting technique. Practitioner summary: An augmented lift (re)training paradigm using tactile cueing and performance feedback regarding key movement features (i.e. lumbar spine flexion) can effectively (re)train a modified lifting technique to reduce lumbar flexion and redistribute motion to the hips and knees. However, performing (re)training while fatigued could slightly hinder learning this lifting technique. [ABSTRACT FROM AUTHOR]

BACKGROUND: The use of home delivery services has expanded due to coronavirus disease – 2019, and couriers' high level of work intensity has become a severe social issue in various nations. OBJECTIVE: This study investigates the risk factors of musculoskeletal disorders (MSDs) caused by frequent loading and unloading actions, known to be the most demanding tasks for couriers. METHODS: A self-report survey and post-hoc interview were employed to collect personal information, task frequency, and the incidence of MSDs. Frequent actions during loading and unloading packages were identified, and the Rapid Entry Body Assessment (REBA) and National Institute for Occupational Safety and Health (NIOSH) lifting equations were assessed. RESULTS: Approximately 29.5% of the 44 subjects suffered from MSDs, and identify the types of actions that frequently occur during loading and unloading packages. According to the REBA survey, 60% of the responses for both loading and unloading are distributed within the risk range of 8–13 points, suggesting a high risk (mean REBA score: 8.8 (loading), 8.5 (unloading)). In every case, NIOSH determined that the lifting index (LI) was harmful (mean LI: 1.62). Thereby, the bending or twisting posture of the hands and neck, long horizontal distance between the packages and the body, and high lifting frequency were identified as major problems. CONCLUSION: The study identified a very high level of musculoskeletal risk for couriers, and the detailed working methods and body parts vulnerable to MSDs. [ABSTRACT FROM AUTHOR]

Optimisation-based predictive models are widely-used to explore the lifting strategies. Existing models incorporated empirical subject-specific posture constraints to improve the prediction accuracy. However, over-reliance on these constraints limits the application of predictive models. This paper proposed a multi-phase optimisation method (MPOM) for two-dimensional sagittally symmetric semi-squat lifting prediction, which decomposes the complete lifting task into three phases—the initial posture, the final posture, and the dynamic lifting phase. The first two phases are predicted with force- and stability-related strategies, and the last phase is predicted with a smoothing-related objective. Box-lifting motions of different box initial heights were collected for validation. The results show that MPOM has better or similar accuracy than the traditional single-phase optimisation (SPOM) of minimum muscular utilisation ratio, and MPOM reduces the reliance on experimental data. MPOM offers the opportunity to improve accuracy at the expense of efforts to determine appropriate weightings in the posture prediction phases. Practitioner summary: Lifting optimisation models are useful to predict and explore the human motion strategies. Existing models rely on empirical subject-specific posture constraints, which limit their applications. A multi-phase model for lifting motion prediction was constructed. This model could accurately predict 2D lifting motions with less reliance on these constraints. [ABSTRACT FROM AUTHOR]

Despite the automatization of many industrial and logistics processes, human workers are still often involved in the manual handling of loads. These activities lead to many work-related disorders that reduce the quality of life and the productivity of aged workers. A biomechanical analysis of such activities is the basis for a detailed estimation of the biomechanical overload, thus enabling focused prevention actions. Thanks to wearable sensor networks, it is now possible to analyze human biomechanics by an inverse dynamics approach in ecological conditions. The purposes of this study are the conceptualization, formulation, and implementation of a deep learning-assisted fully wearable sensor system for an online evaluation of the biomechanical effort that an operator exerts during a manual material handling task. In this paper, we show a novel, computationally efficient algorithm, implemented in ROS, to analyze the biomechanics of the human musculoskeletal systems by an inverse dynamics approach. We also propose a method for estimating the load and its distribution, relying on an egocentric camera and deep learning-based object recognition. This method is suitable for objects of known weight, as is often the case in logistics. Kinematic data, along with foot contact information, are provided by a fully wearable sensor network composed of inertial measurement units. The results show good accuracy and robustness of the system for object detection and grasp recognition, thus providing reliable load estimation for a high-impact field such as logistics. The outcome of the biomechanical analysis is consistent with the literature. However, improvements in gait segmentation are necessary to reduce discontinuities in the estimated lower limb articular wrenches. [ABSTRACT FROM AUTHOR]

Context: The quadratus lumborum ( QL) is expected to contribute to segmental motor control ofthe lumbar spine to prevent low back pain. It has different layers (anterior [QL-a] and posterior [QL-p] layers), whose functional differences are becoming apparent. However, the difference between the QL-a and QL-p activities during bridge exercises utilized in rehabilitation is unclear. Objective : To compare QL - a and QL - p activities during bridge exercises . Design: Repeated-measurement design was used to assess electromyographic activity of trunk muscles recorded during 14 types of bridge exercises . Setting : University laboratory . Participants : A total of 13 healthy men with no history of lumbar spine disorders participated . Intervention. The participants performed 14 types of bridge exercises (3,3, and 8 types of side bridge, back bridge, and front bridge [FB], respectively ). Main Outcome Measures: Fine - wire electromyography was used for QL -a and QL - p activity measurements during bridge exercises . Results : Both QL - a and QLp showed the highest activity during the side bridge with hip abduction (47.3% [29.5%] and 43.0% [32.9%] maximal voluntary isometric contraction, respectively). The activity of the QL-a was significantly higher than that of the QL-p during back bridge with ipsilateral leg lift and FB elbow-toe with ipsilateral arm and contralateral leg lift (P < .05). With regard to the QL-p, the activity of the FB hand-knee with contralateral arm and ipsilateral leg lift, the FB elbow-knee with contralateral arm and ipsilateral leg lift, and the FB elbow-toe with contralateral arm and ipsilateral leg lift were significantly higher than that of the FB elbow -knee and FB elbow-toe (P <. 05 ). Conclusion: This study indicates different regional activities; the QL-a activated during the back bridge with ipsilateral leg lift and FB with ipsilateral arm lift, and the QL-p activated during the FB with ipsilateral leg lift. These results have implications for the rehabilitation of low back pain or lumbar scoliosis patients based on QL recruitment. [ABSTRACT FROM AUTHOR]

The revised NIOSH lifting equation (RNLE) aims to manage lifting-related lower back pain (LBP), by determining safe load limits. Many researchers have studied the multiplier development criteria, the universal applicability of the equation and its ability to identify an increased risk of LBP in lifting tasks. Although a number of strengths of the equation have been highlighted, many limitations have also been identified. The need for new multipliers, such as worker and environmental characteristics, was highlighted in order to make the equation more adaptable. The RNLE was designed to protect 75% of female workers and is therefore inherently conservative. Additionally, as all multipliers have values less than or equal to 1, the recommended weight limits (RWLs) can be further reduced. Thus, new multipliers may be defined, by combining two or more existing multipliers, to make the RWLs more realistic. [ABSTRACT FROM AUTHOR]

Objectives. Findings from previous studies implied that appropriately controlling load knowledge might help improve the biomechanical performance during lifting tasks. However, only load weight knowledge was often discussed in previous studies. The current study aimed to complement the existing studies and provide improved knowledge about the influence of load knowledge on lifting biomechanics. Methods. Twenty-four healthy male participants were recruited and instructed to perform symmetric lifting tasks with different load weights under different load knowledge conditions. Load weights were set at three levels (40, 80 and 120%) of each participant's maximum acceptable lifting capacity. The examined load knowledge conditions included 'no knowledge' condition, 'weight known' condition, 'fragile material known' condition and 'weight and fragile material known' condition. Results. We found that when knowing fragility information about lifting materials, workers tended to be more cautious by adopting a less dynamic motion pattern during the landing phase, as evidenced by decreases of 6–8% in elbow joint acceleration. The 'cautious' lifting pattern when fragility load knowledge was presented could contribute to reduced risk of lower back disorder. Conclusion. This finding could help to develop lower back disorder prevention interventions to improve occupational safety and health. [ABSTRACT FROM AUTHOR]

Individual responses to fatigue have been observed in lifting kinematics, suggesting a subject-specific approach is necessary for fatigue identification. One-class support vector machines (OCSVM) may provide an objective method to classify fatigue-related kinematic changes during repetitive lifting. Participants completed a repetitive lifting protocol while motion capture recorded lifting motions. Subject-specific kinematics from participants' first 35% of lifts trained OCSVM decision boundaries. The remaining lifts were separated into test sets and classified against the decision boundary to identify the percentage of outlier lifts within each test set. Spearman's correlation assessed if the test sets' percentage of outlier lifts increased concurrently with participants' rating of perceived exertion (RPE). Significant positive associations were found for participants who demonstrated evidence of fatigue, while no significant associations were found for participants who did not demonstrate evidence of fatigue. These results demonstrate the prospective efficacy of an outlier detection tool for fatigue detection during repetitive lifting. Practitioner Summary: An objective subject-specific fatigue detection method is desired for workplace tasks, such as lifting. An outlier detection machine learning approach was identified when lifting movement patterns changed from baseline throughout a repetitive lifting protocol. Participants who demonstrated an increase in outlier movement patterns had a concurrent increase in self-reported fatigue. [ABSTRACT FROM AUTHOR]

The aim of the present study was to examine whether relative strength influences lifting kinematics (e.g., lifting time, barbell velocity, vertical displacement) during the bench press (BP) exercise with healthy men. Loaded BP 6-repetition maximum normalized to body mass (i.e., relative strength) was examined in 110 resistance-trained men (age: 22.9 ± 2.5 years, height: 180.9 ± 6.9 cm, body mass: 80.3 ± 7.9 kg), by analysing lifting kinematics using a linear encoder. According to relative BP strength, subjects were classified as beginners, recreationally trained, intermediate, and advanced. Results showed that in the intermediate (p = 0.004, ES = 0.85) and advanced (p = 0.016, ES = 0.81) groups barbell velocity was lower in the sticking region of the BP action, compared with beginners, however there were no significant differences between groups for vertical displacement (p = 0.122–1.000) and lifting time (p = 0.052–1.000). These findings suggest that greater relative strength improves the capacity to perform the eccentric but not the concentric phase of BP. Enhanced barbell lowering indicates that the sticking region is caused by a high demand for eccentric force production during biomechanically disadvantageous conditions. [ABSTRACT FROM AUTHOR]

Objective: The aim of this review was to determine how exoskeletons could assist Australian Defence Force personnel with manual handling tasks. Background: Musculoskeletal injuries due to manual handling are physically damaging to personnel and financially costly to the Australian Defence Force. Exoskeletons may minimize injury risk by supporting, augmenting, and/or amplifying the user's physical abilities. Exoskeletons are therefore of interest in determining how they could support the unique needs of military manual handling personnel. Method: Industrial and military exoskeleton studies from 1990 to 2019 were identified in the literature. This included 67 unique exoskeletons, for which Information about their current state of development was tabulated. Results: Exoskeleton support of manual handling tasks is largely through squat/deadlift (lower limb) systems (64%), with the proposed use case for these being load carrying (42%) and 78% of exoskeletons being active. Human–exoskeleton analysis was the most prevalent form of evaluation (68%) with reported reductions in back muscle activation of 15%–54%. Conclusion: The high frequency of citations of exoskeletons targeting load carrying reflects the need for devices that can support manual handling workers. Exoskeleton evaluation procedures varied across studies making comparisons difficult. The unique considerations for military applications, such as heavy external loads and load asymmetry, suggest that a significant adaptation to current technology or customized military-specific devices would be required for the introduction of exoskeletons into a military setting. Application: Exoskeletons in the literature and their potential to be adapted for application to military manual handling tasks are presented. [ABSTRACT FROM AUTHOR]

Paramedics represent a unique occupational group where the nature of their work, providing prehospital emergency care, makes workplace modifications to manage and control injury risks difficult. Therefore, the provision of workplace education and training to support safe lifting remains a viable and important approach. There is, however, a lack of evidence describing movement strategies that may be optimal for paramedic work. The purpose of this study was to determine if a strategy leveraging a greater contribution of work from the lower body relative to the torso was associated with lower biomechanical exposures on the spine. Twenty-five active duty paramedics performed 3 simulated lifting activities common to paramedic work. Ground reaction forces and whole body kinematics were recorded to calculate: peak spine moment and angle about the L4/L5 flexion-extension axis as indicators of biomechanical exposure; and, joint work, integrated from net joint power as a measure of technique inclusive of movement dynamics. Paramedics generating more work from the lower body, relative to the trunk, were more likely to experience lower peak L4/L5 spine moments and angles. These data can inform the development of workplace training and education on safe lifting that focuses on paramedics generating more work from the lower body. [ABSTRACT FROM AUTHOR]

Lift technique training programs have been implemented to help reduce injury risk, but the underlying content validity of cues used within these programs is not clear. The objective of this study was to determine whether biomechanical variables, that commonly used lifting cues aim to elicit, are associated with resultant low back extensor moment exposures. A sample of 72 participants were recruited to perform 10 repetitions of a floor-to-waist height barbell lift while whole-body kinematics and ground reaction forces were collected. Kinematic, kinetic, and energetic variables representative of characteristics commonly targeted by lifting cues were calculated as predictor variables, while peak and cumulative low back moments were calculated as dependent measures. Multiple regression revealed that 56.6–59.2% of variance in low back moments was explained by predictor variables. From these regression models, generating motion with the legs (both greater hip and knee work), minimizing the horizontal distance of the body to the load, maintaining a stable body position, and minimizing lift time were associated with lower magnitudes of low back moments. These data support that using cues targeting these identified variables may be more effective at reducing peak low back moment exposures via lift training. [ABSTRACT FROM AUTHOR]

In the context of extra-terrestrial missions, the effects of hypogravity (0 < G < 1) on the human body can reduce the well-being of the crew, cause musculoskeletal problems and affect their ability to perform tasks, especially during long-term missions. To date, studies of the effects of hypogravity on human movement are limited to experiments on the lower limbs. Here, we extend the knowledge base to the upper limbs, by conducting experiments to evaluate the effect of hypogravity on upper limb physical fatigue and mental workload in participants. Our hypothesis was that hypogravity would both increase participant productivity, by reducing overall physical fatigue expressed in Endurance Time, and reduce mental workload. Task Intensity-Endurance time curves are developed especially in seated positions, while performing static, dynamic, repetitive tasks. This experiment involved 32 healthy participants without chronic problems of the musculoskeletal system aged 33.59 ± 8.16 years. Using the collected data, fatigue models were constructed for tasks of varying Intensity. In addition, all participants completed the NASA – Task Load Index subjective mental workload assessment, which revealed the level of subjective workload when executing different tasks. We found two trends in the empirical fatigue models associated with the difference between the strength capabilities of males and females. The first is a significant positive (p = 0.002) relation between Endurance time and gravity level (⅙ G Moon, ⅓ G Mars, 1G) with negative coefficient for males and females for a static task. And there is marginal relation (p < 0.1) between overall mental workload and gravity level with a positive coefficient for males and females for the same task. The same trend was observed for dynamic and repetitive tasks. We concluded that the Task Intensity-Endurance Time model, adapted to hypogravity in combination with subjective mental assessment, is useful to human fatigue investigation. The combination of these methods used for ergonomic analysis and digital human modeling, could improve worker productivity. Finally, this study may help prepare astronauts for long-term missions on the Moon and Mars and improve our understanding of how we can prevent musculoskeletal disorders caused by hazardous manual handling under such extreme environments. [ABSTRACT FROM AUTHOR]

Lifting something off the ground is an essential task and lifting is a documented risk factor for low back pain (LBP). The standard lifting techniques are stoop (lifting with your back), squat (lifting with your legs), and semi-squat (midway between stoop and squat). Most clinicians believe the squat technique is optimal; however, training on squat lifting does not prevent LBP and utilizing greater lumbar flexion (i.e. stoop) when lifting is not a risk factor for LBP. The disconnect between what occurs in clinical practice and what the evidence suggests has resulted in ongoing debate. Clinicians must ask the right questions in order to apply the evidence appropriately. A proposed clinical framework of calm tissue down, build tissue up, improve work capacity can be used to determine which lifting technique is optimal for a patient at any given time. When applying this clinical framework, clinicians should consider metabolic, biomechanical, physical stress tolerance, and pain factors in order to address the movement system. For example, stoop lifting is more metabolically efficient and less challenging to the cardiopulmonary system. There may be few biomechanical differences in spinal postures and gross loads on the lumbar spine between stoop, squat, and semi-squat lifting; however, each lift has distinct kinematic patterns that affects muscle activation patterns, and ultimately the movement system. Clinicians must find the optimal dosage of physical stress to address all aspects of the movement system to minimize the risk of injury. There is no universal consensus on the optimal lifting technique which will satisfy every situation; however, there may be a lifting technique that optimizes movement to achieve a specific outcome. The calm tissue down, build tissue up, improve work capacity framework offers an approach to determine the best lifting technique for an individual patient at any give time. [ABSTRACT FROM AUTHOR]

BACKGROUND: Manual demolition tasks are heavy physical demanding tasks which involve forceful exertion of sustained pushing. They result in muscle fatigue which could lead to musculoskeletal disorders. Assessments of maximum endurance time (MET) are essential in understanding the developing of muscle fatigue for these tasks. OBJECTIVE: The objectives of this study were to determine the effects of handle height and load conditions on the MET, and to establish MET models for the simulated demolition tasks. METHODS: Twenty three male participants performed simulated demolition tasks under three loads and three handle heights conditions until they could not do so any longer. Their METs and ratings of perceived exertion were recorded and analyzed. RESULTS: The results showed that both load and handle height were significant (p < 0.0001) factors affecting the MET. Regression models to predict the MET under handle height and load conditions were established. The mean absolute deviations of these models were between 1.91 and 4.84 min. CONCLUSION: The MET models established may be used to estimate the MET which may be adopted in work/rest arrangement for demolition tasks using a handheld demolition hammer. [ABSTRACT FROM AUTHOR]

As we seek to develop high fidelity human simulation models for ergonomic applications, the characterisation of the variability in human performance is needed. This technical note describes a method for generating probability density functions (PDFs) for one performance characteristic: trunk kinematics. A PDF from the Johnson family of distributions is defined by four parameters (γ, ξ, δ and λ) and can represent a variety of distributions. In this study, previously published trunk kinematic data were fit to Johnson distributions and regression equations for each of the four parameters were created as a function of starting lift height. Using regression coefficients and Monte Carlo simulation, PDFs for novel lifting conditions were generated. These predicted PDFs were compared with histograms of empirical data collected from a new group of ten lifters performing lifts in these novel conditions. A Kolmogorov–Smirnov goodness of fit test was performed to assess the quality of the fit. Seven of the predicted distributions of these kinematic variables were found to be a good fit with the novel empirical data. [ABSTRACT FROM AUTHOR]

Body-borne load reportedly increases incidence of military-related knee injury by altering trunk and lower limb biomechanics. This investigation determined whether body-borne load impacts lateral trunk flexion during a single-leg cut, and whether greater lateral trunk flexion exaggerates knee abduction biomechanics. Thirty-six participants had trunk and knee biomechanics quantified during a single-leg cut with four body-borne loads (20, 25, 30 and 35 kg). To evaluate the impact of load on lateral trunk flexion and its relation with knee abduction biomechanics, peak stance lateral trunk flexion was submitted to a linear mixed model with load (20, 25, 30, and 35 kg) and sex (male, female) as fixed effects, and dominant limb peak stance knee abduction joint angle and moment considered as covariates. During the cut, there was a significant sex by load interaction for peak stance lateral trunk flexion (p = 0. 0 3 8), and peak stance lateral trunk flexion angle exhibited a significant association with peak stance knee abduction angle (p < 0. 0 0 1) and moment (p = 0. 0 1 4). Adopting lateral trunk flexion during loaded single-leg cuts may increase knee biomechanics related to ACL injury, but adding load only decreased lateral trunk flexion for female participants and did not further exaggerate knee abduction biomechanics. [ABSTRACT FROM AUTHOR]

Background: The atlas stone lift is a popular strongman exercise where athletes are required to pick up a large, spherical, concrete stone and pass it over a bar or place it on to a ledge. The aim of this study was to use ecologically realistic training loads and set formats to (1) establish the preliminary biomechanical characteristics of athletes performing the atlas stone lift; (2) identify any biomechanical differences between male and female athletes performing the atlas stone lift; and (3) determine temporal and kinematic differences between repetitions of a set of atlas stones of incremental mass. Methods: Kinematic measures of hip, knee and ankle joint angle, and temporal measures of phase and repetition duration were collected whilst 20 experienced strongman athletes (female: n = 8, male: n = 12) performed three sets of four stone lifts of incremental mass (up to 85% one repetition maximum) over a fixed-height bar. Results: The atlas stone lift was categorised in to five phases: the recovery, initial grip, first pull, lap and second pull phase. The atlas stone lift could be biomechanically characterised by maximal hip and moderate knee flexion and ankle dorsiflexion at the beginning of the first pull; moderate hip and knee flexion and moderate ankle plantarflexion at the beginning of the lap phase; moderate hip and maximal knee flexion and ankle dorsiflexion at the beginning of the second pull phase; and maximal hip, knee extension and ankle plantarflexion at lift completion. When compared with male athletes, female athletes most notably exhibited: greater hip flexion at the beginning of the first pull, lap and second pull phase and at lift completion; and a shorter second pull phase duration. Independent of sex, first pull and lap phase hip and ankle range of motion (ROM) were generally smaller in repetition one than the final three repetitions, while phase and total repetition duration increased throughout the set. Two-way interactions between sex and repetition were identified. Male athletes displayed smaller hip ROM during the second pull phase of the first three repetitions when compared with the final repetition and smaller hip extension at lift completion during the first two repetitions when compared with the final two repetitions. Female athletes did not display these between-repetition differences. Conclusions: Some of the between-sex biomechanical differences observed were suggested to be the result of between-sex anthropometric differences. Between-repetition differences observed may be attributed to the increase in stone mass and acute fatigue. The biomechanical characteristics of the atlas stone lift shared similarities with the previously researched Romanian deadlift and front squat. Strongman athletes, coaches and strength and conditioning coaches are recommended to take advantage of these similarities to achieve greater training adaptations and thus performance in the atlas stone lift and its similar movements. [ABSTRACT FROM AUTHOR]

This study explored the influence of different take-off thresholds on the reliability and magnitude of countermovement jump (CMJ) performance variables. Twenty-three men were tested on two separate sessions. CMJ performance variables were obtained against three external loads (0.5–30-60 kg) using three take-off thresholds: 10 N (arbitrary value of 10 N), 5SD (mean value plus 5 standard deviations of the vertical force recorded during the flight phase), and PRF (peak difference between the vertical force trace and 0 N during the flight phase). No significant differences in reliability were observed between the three thresholds (CV and ICC values of one threshold were within 95% CI of the other thresholds). The magnitude of the variables generally differed between the 10 N threshold and the 5SD and PRF thresholds (P <.05), but not between the 5SD and PRF thresholds (P >.05). These results demonstrate that the take-off threshold influences the magnitude of CMJ performance variables but not their reliability. [ABSTRACT FROM AUTHOR]

While evaluating the physical workload on workers, the force exerted needs to be estimated in a convenient way because biomechanical analysis for physical workload evaluation requires data on both posture and exerted force. The aim of this study was to investigate the effectiveness of exerted force estimation using a wearable device that can be easily utilized even by ordinary workers. We measured eight electromyograms (EMGs) on the forearm and the forearm posture with an armband type wearable sensor during manual material handling with varying holding weights and heights. The measurement results showed that the EMGs monotonically increased with an increase in weight. In addition, the EMGs varied with the holding height even when the same weight was held. We constructed an estimation function of the weight using multiple regression analysis. Two sets of explanatory variables were used to investigate the effectiveness of the forearm posture data: the eight EMGs (i.e., SET 1) and the eight EMGs and the two forearm angles (i.e., SET 2). Multiple regression analysis showed that the accuracy of SET 2 was better than that of SET 1. In addition, the average absolute error of the estimation function with SET 2 was 1.49 kg; thus, we concluded that the accuracy of this estimation function has sufficient accuracy for the evaluation of physical workload. [ABSTRACT FROM AUTHOR]

Purpose The Epic Lift Capacity (ELC) test is used to determine a worker's maximum lifting capacity. In the ELC test, maximum lifting capacity is often determined as the maximum weight lifted without exhibiting a visually appraised "high-risk workstyle." However, the criteria for evaluating lifting mechanics have limited justification. This study applies feature detection and biomechanical analysis to motion capture data obtained while participants performed the ELC test to objectively identify aspects of movement that may help define "high-risk workstyle". Method In this cross-sectional study, 24 participants completed the ELC test. We applied Principal Component Analysis, as a feature detection approach, and biomechanical analysis to motion capture data to objectively identify movement features related to biomechanical exposure on the low back and shoulders. Principal component scores were compared between high and low exposure trials (relative to median exposure) to determine if features of movement differed. Features were interpreted using single component reconstructions of principal components. Results Statistical testing showed that low exposure lifts and lowers maintained the body closer to the load, exhibited squat-like movement (greater knee flexion, wider base of support), and remained closer to neutral posture at the low back (less forward flexion and axial twist) and shoulder (less flexion and abduction). Conclusions Use of feature detection and biomechanical analyses revealed movement features related to biomechanical exposure at the low back and shoulders. The objectively identified criteria could augment the existing scoring criteria for ELC test technique assessment. In the future, such features can inform the design of classifiers to objectively identify "high-risk workstyle" in real-time. [ABSTRACT FROM AUTHOR]

Physically demanding and repetitive tasks expose workers to work-related musculoskeletal disorders (WMSDs). Over the last few decades, various rule-based postural assessment systems have been developed and widely used to facilitate the measurement and evaluation of risks related to WMSDs in many industries. However, the applicability of rule-based assessment to tasks involving heavy material handling has not yet been examined. This study investigated the applicability of three rule-based assessment systems (RULA, REBA, and OWAS) to a bricklaying task. To achieve this goal, an automated assessment tool was developed to implement those systems on whole-body data sets consisting of static postures captured by wearable inertial measurement unit suits. The study demonstrates the use of this tool in assessing risk levels (grand scores) encountered by 43 masons during the laying of 16.6-kg concrete masonry units (CMUs) in a standard wall. Furthermore, the biomechanical analysis of the same data set was carried out and utilized as ground truth to evaluate those results. It was found that rule-based assessment may lead to erroneously inflated risk evaluation in heavy manual handling tasks. In contrast, biomechanical analysis provided sensitive risk evaluations that distinguish the different degrees of risk arising from different motion patterns while participants performed the same tasks. These findings suggest using biomechanical analysis as an objective and robust method to evaluate risks encountered in tasks involving heavy material handling. [ABSTRACT FROM AUTHOR]

The primary aims of the study were to (a) quantify the effect of load magnitude on lumbopelvic-hip complex (LPHC) and scapular muscle activation and (b) quantify the effect of different carry positions on bilateral glutei medii (GM) and external oblique (EO) activation during unilateral dumbbell carries. Eighteen resistance-trained individuals (22.662.6 years) completed 3 trials of 3 carry positions (overhead, frontracked, and suitcase) with 3 load conditions (light, moderate, and heavy) across a twelve-meter distance with the dumbbell held on the subject’s dominant side. Electromyographic data were collected on the dominant upper (UT) and lower trapezius (LT), latissimus dorsi (LD), and serratus anterior (SA) as well as bilateral GM and EO. Repeated measures analysis of variance revealed a significant load by muscle interaction [F(14, 81.931) 5 15.474; p, 0.001; ηp² 5 0.477]. Follow-up pairwise comparisons revealed increased muscle activation with increased load acrossmostmuscles. There was also a significantmuscle by position interaction for bilateralGMand EO [GM: F(1.157, 19.662) 520.240; p,0.001; ηp² 50.544] [EO: F(1.302, 22.129)525.620; p,0.001; ηp² 50.601]. Post-hoc analysis revealed bilateral differences in muscle activation for the GM in the suitcase position and for the EO in the overhead and suitcase position, where the nondominant side showed significantly greater activation (all p, 0.039). These findings suggest unilateral carries may be used to target LPHC and scapular muscle activation; however, load and carry position should be considered because variations affect muscle activation. [ABSTRACT FROM AUTHOR]

Occupational exoskeletons and exosuits have been shown to reduce muscle demands and fatigue for physical tasks relevant to a variety of industries (e.g., logistics, construction, manufacturing, military, healthcare). However, adoption of these devices into the workforce has been slowed by practical factors related to comfort, form-factor, weight, and not interfering with movement or posture. We previously introduced a low-profile, dual-mode exosuit comprised of textile and elastic materials to address these adoption barriers. Here we build upon this prior work by introducing an extension mechanism that increases the moment arm of the exosuit while in engaged mode, then collapses in disengaged mode to retain key benefits related to being lightweight, low-profile, and unobstructive. Here we demonstrate both analytically and empirically how this extensible exosuit concept can (a) reduce device-to-body forces (which can improve comfort for some users and situations), or (b) increase the magnitude of torque assistance about the low back (which may be valuable for heavy-lifting jobs) without increasing shoulder or leg forces relative to the prior form-fitting exosuit. We also introduce a novel mode-switching mechanism, as well as a human-exosuit biomechanical model to elucidate how individual design parameters affect exosuit assistance torque and device-tobody forces. The proof-of-concept prototype, case study, and modeling work provide a foundation for understanding and implementing extensible exosuits for a broad range of applications. We envision promising opportunities to apply this new dual-mode extensible exosuit concept to assist heavy-lifting, to further enhance user comfort, and to address the unique needs of last-mile and other delivery workers. [ABSTRACT FROM AUTHOR]

Prolonged or repetitive spine flexion induces creep deformation of posterior spine tissues allowing for increased intervertebral motion beyond 'normal' limits, which may influence sub-regional (intersegmental) spine motion during subsequent manual lifting tasks. Using spine skin-surface kinematics, intersegmental lumbar spine motion was recorded over 20 minutes of prolonged static spine flexion and a subsequent manual lifting task (2 lifts every 3 minutes, 30 minutes total) in 14 participants. Results demonstrated that mid to lower lumbar intersegmental levels (i.e. L2/L3 to L4/L5) experienced the greatest overall creep deformation and range of motion during both prolonged flexion and manual lifting; however, overall range of motion during manual lifting was unaffected. Additionally, creep deformation did not completely recover within 30 minutes. Future work should continue to investigate the influence of this residual creep, as well as how overall creep deformation impacts spine neuromuscular control and stability, and ultimately the development of low back disorders. Practitioner summary: Mid to lower lumbar spine levels (i.e. L2/L3 to L4/L5) experienced the greatest creep deformation and range of motion during both prolonged flexion and manual lifting. Repeated lifting following prolonged flexion may limit creep recovery; however, overall lifting kinematic motion remained unchanged. [ABSTRACT FROM AUTHOR]

Background: Intrinsic factors including altered joint motion in the upper extremity may lead to altered biomechanics in tennis players and could result in symptoms of lateral elbow tendinopathy. Purpose: To compare upper extremity passive motion and elbow carrying angle between three groups of women: recreational tennis players with LET, non-symptomatic recreational tennis players, and a control group of non-tennis players. Study Design: Cross-sectional. Methods: A convenience sample of 63 women was recruited and placed into one of the three groups: nonsymptomatic tennis players (NSTP), symptomatic tennis players (STP), and a control group. Elbow carrying angle, passive range of motion of the shoulder, elbow, forearm, and wrist were measured during a single session. Results: A significant difference was found between the groups for wrist flexion (p < 0.00), forearm pronation (p = 0.002), elbow flexion (p = 0.020) and extension (p = 0.460), as well as shoulder internal rotation (p < 0.00). No significant differences were found in other motions or carrying angle between the three groups (p =0.059). Post-hoc comparisons indicated that shoulder internal rotation and wrist flexion was less in both STP and NSTP groups compared with the control group. Elbow flexion and forearm pronation were greater in STP than the other two groups. Conclusion: Impairments including loss of shoulder internal rotation and wrist flexion and greater motion at the elbow and forearm were found in the UE of symptomatic tennis players. Evaluation of passive motion and muscle length should be performed prior to establishing a rehabilitation plan for symptomatic tennis players. [ABSTRACT FROM AUTHOR]

Background: Human babies are carried by their caregivers during infancy, and the use of ergonomic aids to wear the baby on the body has recently grown in popularity. However, the effects of wearing or holding a baby in-arms on an individual's mechanics during gait and a common object retrieval task are not fully understood.Research Question: What are the differences in: 1) spatiotemporal, lower extremity kinematics, and ground reaction force variables during gait, and 2) technique, center of mass motion, and kinematics during an object retrieval task between holding and wearing an infant mannequin?Methods: In this prospective biomechanics study, 10 healthy females performed over-ground walking and an object retrieval task in three conditions, holding: (1) nothing (unloaded), (2) an infant mannequin in-arms, and (3) an infant mannequin in a baby carrier. Mechanics were compared using repeated measures ANOVA.Results: During gait, greater vertical ground reaction force and impulse and braking force was found during the in-arms and carrier conditions compared to unloaded. Significant but small (<5°) differences were found between conditions in lower extremity kinematics. Increased back extension was found during carrier and in-arms compared to unloaded. Step length was the only spatiotemporal parameter that differed between conditions. During object retrieval, most participants used a squatting technique to retrieve the object from the floor. They maintained a more upright posture, with less trunk flexion and anteroposterior movement of their center of mass, and also did not try to fold forward over their hips during the two loaded conditions. Lower extremity kinematics did not differ between unloaded and carrier, suggesting that babywearing may promote more similar lower extremity mechanics to not carrying anything.Significance: Holding or wearing an infant provides a mechanical constraint that impacts the forces and kinematics, which has implications for caregivers' pain and dysfunction. [ABSTRACT FROM AUTHOR]

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Background. The physical demands associated with patient handling activities have been well documented in healthcare. However, many activities contribute to the physical demands of caregivers. Our purpose was to evaluate upper extremity muscle activity and kinematics during intravenous (IV) pole interaction. Materials and methods. Muscle activity was measured from six muscles using surface electromyography and joint kinematics were measured using motion capture. Participants performed two IV pole tasks: loading an IV bag and a medical device onto the pole. Two poles were evaluated: a traditional IV pole and a redesigned pole with ergonomic considerations. Results. Cervical extensor activity was significantly greater for the bag task with the traditional pole (43.29 ± 5.10% maximal voluntary exertion) compared to the redesigned pole (28.55 ± 3.42% maximal voluntary exertion). Peak right shoulder flexion was reduced from 102.88° ± 32.42° with the traditional pole to 55.44° ± 19.59° with the redesigned pole. Conclusion. Interactions with a traditional pole are comparable to upper extremity muscle activity during manual patient handling transfers. The redesigned pole reduced shoulder flexion during bag attachment, leading to less time in an overhead posture. Caregivers frequently interact with IV poles and reducing the physical demands associated with pole use could aid in a reduction of musculoskeletal disorders. [ABSTRACT FROM AUTHOR]

In military life, load carriage is an unavoidable part of field operations which is the reason why soldiers often make use of a military backpack. Infantry soldiers usually carry loads weighting more than 30% of their body weight. When the soldier carries a certain weight, his energy expenditure increases, which causes a reduction in performance. The transported load has a movement similar to the vertical displacement of the center of mass of the soldier while walking. This leads to a significant increase in the acceleration forces generated by the action of said load on the body which explains the increase in energy expenditure. The objective of this project was to develop a load carriage system that suspends the load and reduces its vertical displacement. Results show a reduction in both the vertical excursion of the load and in the total vertical ground reaction force when carrying a load with the developed prototype, with respect to the conventional military backpack. [ABSTRACT FROM AUTHOR]

The objectives of this study were to quantify loads imposed upon the lumbar spine while lifting/lowering with one versus two hands and to create guidelines for one-handed lifting/lowering that are protective of the lower back. Thirty subjects (15 male, 15 female) performed one- and two-handed exertions in a laboratory, lifting from/lowering to 18 lift origins/destinations using medicine balls of varying masses. An electromyography-assisted model predicted peak spinal loads, which were related to tissue tolerance limits to create recommended weight limits. Compared to two-handed exertions, one-handed exertions resulted in decreased spinal compression and A/P shear loading (p < 0.001) but increased lateral shear (p < 0.001). Effects were likely driven by altered moment exposures attributable to altered torso kinematics. Differences between spinal loads for one- versus two-handed exertions were influenced by asymmetry (p < 0.001) and amplified at lower lift origin/destination heights, lower object masses and larger horizontal distances between the body and the load (p < 0.001). Practitioner summary: A biomechanical model was utilised to compare spinal loading for one versus two-handed lifting/lowering. Spinal loads in compression and A/P shear were reduced for one-handed relative to two-handed exertions. As current lifting guidelines cannot appropriately be applied to one-handed scenarios, one-handed weight limits protecting the lower back are presented herein. Abbreviations: LBD: low back disorder, EMG: electromyography, A/P: anterior/posterior, MVC: maximum voluntary contraction [ABSTRACT FROM AUTHOR]

Study Design: A biomechanical analysis correlating internal disc strains and tissue damage during simulated repetitive lifting.Objective: To understand the failure modes during simulated safe and unsafe repetitive lifting.Summary Of Background Data: Repetitive lifting has been shown to lead to lumbar disc herniation (LDH). In vitro studies have developed a qualitative understanding of the effect of repetitive loading on LDH. However, no studies have measured internal disc strains and subsequently correlated these with disc damage.Methods: Thirty human cadaver lumbar functional spinal units were subjected to an equivalent of 1 year of simulated repetitive lifting under safe and unsafe levels of compression, in combination with flexion (13-15°), and right axial rotation (2°) for 20,000 cycles or until failure. Safe or unsafe lifting were applied as a compressive load to mimic holding a 20 kg weight either close to, or at arm's length, from the body, respectively. Maximum shear strains (MSS) were measured, and disc damage scores were determined in nine regions from axial post-test magnetic resonance imaging (MRI) and macroscopic images.Results: Twenty percent of specimens in the safe lifting group failed before 20,000 cycles due to endplate failure, compared with 67% in the unsafe group. Over half of the specimens in the safe lifting group failed via either disc protrusion or LDH, compared with only 20% via protrusion in the unsafe group. Significant positive correlations were found between MRI and macroscopic damage scores in all regions (rs > 0.385, P < 0.049). A significant positive correlation was observed in the left lateral region for MSS versus macroscopic damage score (rs = 0.486, P < 0.037) and MSS versus failure mode (rs = 0.724, P = 0.018, only specimens with disc failure). Pfirrmann Grade 3 discs were strongly associated with subsequent LDH (P = 0.003).Conclusion: Increased shear strains were observed in the contralateral side to the applied rotation as disc injury progressed from protrusion to LDH. Larger compressive loads applied to simulate unsafe lifting led to frequent early failure of the endplate, however, smaller compressive loads at similar flexion angles applied under safe lifting led to more loading cycles before failure, where the site of failure was more likely to be the disc. Our study demonstrated that unsafe lifting leads to greater risk of injury compared with safe lifting, and LDH and disc protrusion were more common in the posterior/posterolateral regions.Level Of Evidence: N/A. [ABSTRACT FROM AUTHOR]

Objectives Varied work-related musculoskeletal disorders (WMSDs) claim rates were found between companies even when they were in the same sectors with similar sizes. This study aimed to (i) identify common risk factors for back, shoulder, hand/wrist, and knee WMSDs among manufacturing jobs, and (ii) characterize the biomechanical exposures in jobs and work organizational practices between high and low WMSD claim rate companies so that more focused, industry-specific intervention strategies may be developed. Methods Using historical workers' compensation data, manufacturing companies were divided into two paired groups (low and high in the lower 25%ile and higher 75%ile, respectively). On-site job evaluations were conducted in 16 companies to determine job biomechanical risk levels. Management and workers' representatives in 32 paired companies were interviewed to identify possible differences between management strategies and management/worker relationships. A total of 39 injured workers were also interviewed to gather information of self-reported injury causes and suggested preventive measures. Results Analyses of 432 job evaluations showed that more jobs had higher risk levels of prolonged standing and heavy lifting in the high back WMSD claim rate companies than the low claim rate ones. No high biomechanical risk factors were found to be associated with jobs in high shoulder claim rate companies. High repetition, pinch force, and Strain Index were associated with high hand/wrist WMSD claim rate companies. High work pace and job stress were common among high knee WMSD claim rate companies. There were no statistically significant differences for the organizational factors between high and low WMSD claim rate companies. Heavy lifting, fast work pace, high hand/wrist repetition, high hand force, and awkward shoulder postures were identified as major contributing factors by the injured workers. Conclusions High WMSD claim rate companies appeared to have more high biomechanical exposure jobs than low WMSD claim rate companies. Available job evaluation methods for the low back and hand/wrists are satisfactory in quantifying job risk levels in the manufacturing industry. Research into more sensitive job evaluation methods for the shoulder and knee are needed. [ABSTRACT FROM AUTHOR]

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 [ABSTRACT FROM AUTHOR]

Farm youth often carry loads that are proportionally large and/or heavy, and field measurements have determined that these tasks are equivalent to industrial jobs with high injury risks. The purpose of this study was to determine the effects of age, load amount, and load symmetry on lower extremity joint moments during carrying tasks. Three age groups (8-10 years, 12-14 years, adults), three load amounts (0%, 10%, 20% BW), and three load symmetry levels (unilateral large bucket, unilateral small bucket, bilateral small buckets) were tested. Inverse dynamics was used to determine maximum ankle, knee, and hip joint moments. Ankle dorsiflexion, ankle inversion, ankle eversion, knee adduction, and hip extension moments were significantly higher in 8-10 and 12-14 year olds. Ankle plantar flexion, ankle inversion, knee extension, and hip extension moments were significantly increased at 10% and 20% BW loads. Knee and hip adduction moments were significantly increased at 10% and 20% BW loads when carrying a unilateral large bucket. Of particular concern are increased ankle inversion and eversion moments for children, along with increased knee and hip adduction moments for heavy, asymmetrical carrying tasks. Carrying loads bilaterally instead of unilaterally avoided increases in knee and hip adduction moments with increased load amount. [ABSTRACT FROM AUTHOR]

Farm youth commonly perform animal care tasks such as feeding and watering. The purpose of this study was to determine the effects of age, bucket size, loading symmetry, and amount of load on upper body moments during carrying tasks. Fifty-four male and female participants in four age groups (8-10 years, 12-14 years, 15-17 years, and adults, 20-26 years) participated in the study. Conditions included combinations of large or small bucket sizes, unilateral or bilateral loading, and load levels of 10% or 20% of body weight (BW). During bucket carrying, elbow flexion, shoulder flexion, shoulder abduction, shoulder external rotation, L5/S1 extension, L5/S1 lateral bending, and L5/S1 axial rotation moments were estimated using video data. The 8-10 year-old group did not display higher proportional joint moments as compared with adults. Decreasing the load from 20% BW to 10% BW significantly decreased maximum normalized elbow flexion, shoulder flexion, shoulder abduction, shoulder external rotation, L5/S1 lateral bending, and L5/S1 axial rotation moments. Carrying the load bilaterally instead of unilaterally also significantly reduced these six maximum normalized joint moments. In addition, modifying the carrying task by using smaller onegallon buckets produced significant reductions in maximum L5/S1 lateral bending moments. [ABSTRACT FROM AUTHOR]

The start from blocks is a fundamental component of all track and field sprint events (≤ 400 m). This narrative review focusses on biomechanical aspects of the block phase and the subsequent first flight and stance phases. We discuss specific features of technique and how they may be important for a high level of performance during the start. The need to appropriately quantify performance is discussed first; external power has recently become more frequently adopted because it provides a single measure that appropriately accounts for the requirement to increase horizontal velocity as much as possible in as little time as possible. In the "set" position, a relatively wide range of body configurations are adopted by sprinters irrespective of their ability level, and between-sprinter differences in these general positions do not appear to be directly associated with block phase performance. Greater average force production during the push against the blocks, especially from the rear leg and particularly the hip, appears to be important for performance. Immediately after exiting the blocks, shorter first flight durations and longer first stance durations (allowing more time to generate propulsive force) are found in sprinters of a higher performance level. During the first stance phase, the ankle and knee both appear to play an important role in energy generation, and higher levels of performance may be associated with a stiffer ankle joint and the ability to extend the knee throughout stance. However, the role of the sprinter's body configuration at touchdown remains unclear, and the roles of strength and anatomy in these associations between technique and performance also remain largely unexplored. Other aspects such as the sex, age and performance level of the studied sprinters, as well as issues with measurement and comparisons with athletes with amputations, are also briefly considered. [ABSTRACT FROM AUTHOR]