Gender differences in lifting technique

Quantifying how functional and structural personal factors influence biomechanical exposures in paramedic lifting tasks

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.

Simulation analysis of low back forces in Snatch and Clean & Jerk movements via digital human modelling

BACKGROUND

Weightlifting is an Olympic sport for dynamic strength and power, and requires the execution of different lifting techniques It is important to analyze the forces subjected to the lower back during weightlifting movements to prevent injuries. Digital Human Modeling (DHM) is a powerful tool that can be used to analyze and optimize the performance of humans while doing their work or activities.

OBJECTIVE

The purpose of this study is to present a simulation analysis of the lower back forces during the execution of two weightlifting techniques: Snatch (SN) and Clean & Jerk (CJ), with different loads and for both genders.

METHODS

Digital Human modelling through JACK simulation package was used analyze the forces exerted on the lumbosacral area (L5-S1) of the lower back in order to determine the risk for low back injuries. The level of compression and shear forces recommended by the literature have been set as thresholds. The simulaitons were performed in male and female models, with loads from 20-100 kg.

RESULTS

The results show that any weight higher than 60 kg in both movements poses risk for the weightlifters in terms of compression and shear forces. It has been observed that weightlifters can lift greater loads in the CJ technique compared to the SN technique. Furthermore, females are able to lift higher loads with lower risk of injuries.

CONCLUSION

Weightlifting is a high-risk activity due to the high levels of shear and compression forces that the body is exposed to during the lifting techniques. Digital Human Modeling holds significant value due to their ability to facilitate the exploration of diverse conditions within a safe environment, devoid of any potential harm to human subjects.

Effect of strengthening and weakening of abdominal and dorsal muscles on lumbar spine loads in parents of disabled children

Pain in the lower part of the back is one of the most common chronic illnesses globally. This work aimed to determine the impact of the reinforcement of particular groups of abdominal and dorsal muscles on the loads exerted on the lumbar section of the spine in 30 mothers of children with motor disabilities. An optical Ariel Performance Analysis System recorded and processed the kinematics data of everyday activities. Tests investigating the effects of the strengthening or weakening of abdominal and dorsal muscles on loading in the lumbar section of the spine utilized the AnyBody Modelling System. Input data for the simulations included mean values of body positions, while the effects of strengthening or weakening of muscles were simulated in the muscle forces model by introducing different values for muscle physiological cross-sectional area (PCSA). Simulations used decreasing or increasing PCSA values of abdominal muscles and the erector spinae. The analysis involved component and resultant force values on the lumbosacral joint (L5-S1) of the spine and intra-abdominal pressure values. The highest reduction of the resultant reaction value in L5-S1 was observed in the simulations that increased the PCSA of the transverse abdominal (TrA). Indeed, a double increase in the TrA cross-section caused a reduction of the resultant reaction in L5-S1 by 30% and the anterior-posterior and proximal-distal forces by approximately 20-30%. Increased PCSA of the erector spinae exerted higher loads on the spine. These results indicate that strengthening weakened abdominal muscles, particularly TrA, in parents of children with motor disabilities reduces lower spinal loads during daily activities.

Revised NIOSH lifting equation: a critical evaluation

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.

Redesign and ergonomic assessment of a chest-support baby walker

BACKGROUND

Parents often use baby walkers (BWs) as assistive devices to improve their infants' independent movement and motor skill acquisition. However, the literature suggests that conventional baby walkers (CBW) may cause delays in an infant's ability to walk independently and musculoskeletal burden on parents.

OBJECTIVE

In the current study, a baby walker (RBW) with chest support was redesigned and ergonomically assessed during an infant-walking task.

METHODS

The anthropometric dimensions of 90 infants aged 7-11 months were measured in the city of Urmia, northwestern Iran. Following redesigning based on the results from expert panel meetings and prototyping of the RBW, 18 mothers (age: 28.33±4.27 and height: 163.75±5.32 and weight: 59.45±5.99) with their infants (9 boys and 9 girls) performed a simulated infant walking task in two experimental sessions using the CBW and RBW over a repeated measurements design. The infants' feet track patterns, including the number of steps and step distances were assessed via the image analysis of the footprints. The mothers' body posture and lower back spinal load were evaluated using Rapid Upper Limb Assessment (RULA) technique and 3D Static Strength Prediction Program (3DSSPP), respectively.

RESULTS

Wilcoxon signed-rank tests showed infants walked more steps with the RBW (p = 0.002). Similarly, the distance between the infants' left heel strike (p = 0.008) and their right and left toe-off (p = 0.03 and 0.02 respectively) was also significantly lower in the RBW use. Additionally, the body posture of mothers was improved (RULA final score from 7 for CBW to 5 for RBW). Moreover, lower back compression and shear forces were reduced significantly (p = 0.002) by the RBW use.

CONCLUSION

According to the feet track pattern, infants took more balanced steps when the RBW was used. In addition, mothers were subjected to less pressure on the lumbar region when they placed and lifted their infant from the RBW. However, further work is necessary to investigate potential long-term effects of the RBWs use.

Shoulder pain, shoulder disability, and depression as serial mediators between stress and health-related quality of life among middle-aged women

This study analyzed the mediating effects of shoulder pain, disability, and depression on the relationship between stress and health-related quality of life among middle-aged women using a serial mediation model. Methods. Data on stress, health-related quality of life, shoulder pain, shoulder disability, and depression were collected from 565 women aged 35–64 years living in Seoul, South Korea, from May 13 to 23, 2021, using a self-reported, structured survey. SPSS PROCESS macro (Model 6) and serial mediation analysis were used to analyze the relationship between stress and health-related quality of life among participants, with shoulder pain, shoulder disability, and depression as mediators. Results. The results indicate that stress had a statistically direct impact on health-related quality of life. In the serial mediation analysis, shoulder pain, disability, and depression were found to be statistically significant, thus affecting the relationship between stress and health-related quality of life, with an explanatory power of 33%. Therefore, the relationship between stress and health-related quality of life was partially mediated by these variables. Conclusions. Thus, this study suggests the need for healthcare workers to develop methods, such as exercise intervention programs based on various degrees and types of physical activity, to improve health-related quality of life and reduce stress caused by shoulder pain, shoulder disability, and depression among middle-aged women.

Thoracolumbar And Lumbopelvic Spinal Alignment During The Deadlift Exercise: A Comparison Between Men And Women

Background

A neutral spinal alignment is considered important during the execution of the deadlift exercise to decrease the risk of injury. Since male and female powerlifters experience pain in different parts of their backs, it is important to examine whether men and women differ in spinal alignment during the deadlift.

Objectives

The purpose of this study was to quantify the spinal alignment in the upper (thoracolumbar, T11-L2) and lower (lumbopelvic, L2-S2) lumbar spine during the deadlift exercise in male and female lifters. Secondary aims were to compare lumbar spine alignment during the deadlift to standing habitual posture, and determine whether male and female lifters differ in these aspects.

Study Design

Observational, Cross-sectional.

Methods

Twenty-four (14 men, 10 women) lifters performed three repetitions of the deadlift exercise using 70% of their respective one-repetition maximum. Spinal alignment and spinal range of motion were measured using three inertial measurement units placed on the thoracic, lumbar and sacral spine. Data from three different positions were analyzed; habitual posture in standing, and start and stop positions of the deadlift, i.e. bottom and finish position respectively.

Results

During the deadlift, spinal adjustments were evident in all three planes of movement. From standing habitual posture to the start position the lumbar lordosis decreased 13° in the upper and 20° in the lower lumbar spine. From start position to stop position the total range of motion in the sagittal plane was 11° in the upper and 22° in the lower lumbar spine. The decreased lumbar lordosis from standing habitual posture to the start position was significantly greater among men.

Conclusions

Men and women adjust their spinal alignment in all three planes of movement when performing a deadlift and men seem to make greater adjustments from their standing habitual posture to start position in the sagittal plane.

Level of Evidence

3.

The influence of sex and strength capacity on normalized low-back exposure during lifting: Insights from a joint power analysis

OBJECTIVE

Investigate the influence of sex, strength capacity, and relative load mass on low-back exposure and lower extremity joint power generation in backboard lifting.

BACKGROUND

Sex and strength have been shown to influence lifting strategy, but without load mass being scaled to strength it is unknown which factor influences low-back exposures, and whether there are interactions with load mass.

METHODS

Motion capture and force plate data from 28 participants were collected during backboard lifting at load masses scaled to strength capacity. Differences in normalized peak low-back moment, peak knee-to-hip power magnitude ratio and timing were tested as a function of sex, strength, and load mass.

RESULTS

Stronger participants had lower normalized peak low-back moments (average 32% change from low-capacity across all load masses), with no significant sex effect (p = 0.582). As load mass increased, normalized peak low-back moment, peak knee-to-hip power magnitude and synchronicity decreased.

CONCLUSION

Training to both increase strength capacity and hip-joint power generation may be a strategy to reduce low-back exposure in backboard lifting.

Ergonomic Design of Apron Bus with Consideration for Passengers with Mobility Constraints

Passengers in an apron bus are usually subjected to a standing position because of its limited seats and capacity. Due to this, passengers, especially those with mobility constraints, may expose themselves to musculoskeletal disorder (MSD) risks such as body pain, discomfort, and non-collision injuries. The purpose of this study is to design an ergonomic apron bus to aid the musculoskeletal discomfort experienced by passengers with mobility constraints, specifically the elderly, pregnant women, mothers carrying infants, and persons needing wheelchair assistance. A total of 149 participants are involved in the study. Corlett’s and Bishop’s body discomfort questionnaires and Rapid Entire Body Assessment (REBA) are utilized to evaluate the respondent’s experience of discomfort in different regions of their body. The results show that passengers with mobility constraints experience body discomfort during the apron bus ride. The prevalence of body discomfort is evident in the lower back, knee, thigh, arm, shoulder, and middle back. Finally, principles of anthropometry are used in the study along with quality function deployment (QFD), failure mode and effects analysis (FMEA), and cost-benefit analysis to evaluate the feasibility of the recommended ergonomic design of the apron bus. To meet the requirements of people with disabilities, the ergonomic design of an apron bus is created to minimize the risk of exposure of passengers to certain musculoskeletal discomfort, maximize the space, minimize the delay time of the airlines, and be able to prioritize passengers who require mobility assistance.

The influence of hip flexion mobility and lumbar spine extensor strength on lumbar spine flexion during a squat lift

STUDY DESIGN

Cross-sectional; Controlled laboratory study.

OBJECTIVE

To examine the associations among available hip flexion motion, lumbar extensor strength and peak lumbar flexion during a squat lift task.

SUMMARY OF BACKGROUND DATA

Lumbar spine flexion during lifting can result in increased strain on spinal structures. Although decreased available hip flexion motion and reduced strength of the lumbar extensor muscles has been proposed to contribute to greater lumbar flexion during lifting, direct relationships have not been explored.

METHODS

Fifty healthy young adults participated (23 males and 27 females). Strength of the lumbar extensors was measured using a motor-driven dynamometer. Available hip flexion was assessed using 3D motion capture. Peak lumbar spine flexion and hip flexion were quantified during the descent phase of the squat lifting task.

RESULTS

There was a significant negative association between available hip flexion and peak lumbar spine flexion during squat lifting in females (r = -0.407, p = 0.035) but not males (r = -0.341, p = 0.120). Similarly, peak lumbar spine flexion was negatively associated with lumbar extensor strength in females (r = -0.398, p = 0.040) but not males (r = -0.310, p = 0.161). During the squat lift, peak hip motion was positively associated with available hip flexion for both males and females combined (r = 0.774, p < 0.001).

CONCLUSION

Females with less available hip flexion and lower lumbar extensor strength exhibit greater lumbar flexion when performing a lifting task. Clinicians should be aware of the potential contributions of such impairments when instructing patients into various lifting strategies.

Comparative Analysis of Optoelectronic Accuracy in the Laboratory Setting Versus Clinical Operative Environment: A Systematic Review

STUDY DESIGN

Systematic review.

OBJECTIVES

The optoelectronic camera source and data interpolation process serve as the foundation for navigational integrity in robotic-assisted surgical platforms. The current systematic review serves to provide a basis for the numerical disparity observed when comparing the intrinsic accuracy of optoelectronic cameras versus accuracy in the laboratory setting and clinical operative environments.

METHODS

Review of the PubMed and Cochrane Library research databases was performed. The exhaustive literature compilation obtained was then vetted to reduce redundancies and categorized into topics of intrinsic accuracy, registration accuracy, musculoskeletal kinematic platforms, and clinical operative platforms.

RESULTS

A total of 465 references were vetted and 137 comprise the basis for the current analysis. Regardless of application, the common denominators affecting overall optoelectronic accuracy are intrinsic accuracy, registration accuracy, and application accuracy. Intrinsic accuracy equaled or was less than 0.1 mm translation and 0.1 degrees rotation per fiducial. Controlled laboratory platforms reported 0.1 to 0.5 mm translation and 0.1 to 1.0 degrees rotation per array. Accuracy in robotic-assisted spinal surgery reported 1.5 to 6.0 mm translation and 1.5 to 5.0 degrees rotation when comparing planned to final implant position.

CONCLUSIONS

Navigational integrity and maintenance of fidelity of optoelectronic data is the cornerstone of robotic-assisted spinal surgery. Transitioning from controlled laboratory to clinical operative environments requires an increased number of steps in the optoelectronic kinematic chain and error potential. Diligence in planning, fiducial positioning, system registration and intra-operative workflow have the potential to improve accuracy and decrease disparity between planned and final implant position.

Sex-Dependent Estimation of Spinal Loads During Static Manual Material Handling Activities-Combined in vivo and in silico Analyses

Manual material handling (MMH) is considered as one of the main contributors to low back pain. While males traditionally perform MMH tasks, recently the number of females who undertake these physically-demanding activities is also increasing. To evaluate the risk of mechanical injuries, the majority of previous studies have estimated spinal forces using different modeling approaches that mostly focus on male individuals. Notable sex-dependent differences have, however, been reported in torso muscle strength and anatomy, segmental mass distribution, as well as lifting strategy during MMH. Therefore, this study aimed to use sex-specific models to estimate lumbar spinal and muscle forces during static MHH tasks in 10 healthy males and 10 females. Motion-capture, surface electromyographic from select trunk muscles, and ground reaction force data were simultaneously collected while subjects performed twelve symmetric and asymmetric static lifting (10 kg) tasks. AnyBody Modeling System was used to develop base-models (subject-specific segmental length, muscle architecture, and kinematics data) for both sexes. For females, female-specific models were also developed by taking into account for the female’s muscle physiological cross-sectional areas, segmental mass distributions, and body fat percentage. Males showed higher absolute L5-S1 compressive and shear loads as compared to both female base-models (25.3% compressive and 14% shear) and female-specific models (41% compressive and 23.6% shear). When the predicted spine loads were normalized to subjects’ body weight, however, female base-models showed larger loads (9% compressive and 16.2% shear on average), and female-specific models showed 2.4% smaller and 9.4% larger loads than males. Females showed larger forces in oblique abdominal muscles during both symmetric and asymmetric lifting tasks, while males had larger back extensor muscle forces during symmetric lifting tasks. A stronger correlation between measured and predicted muscle activities was found in females than males. Results indicate that female-specific characteristics affect the predicted spinal loads and must be considered in musculoskeletal models. Neglecting sex-specific parameters in these models could lead to the overestimation of spinal loads in females.

The influence of hip extensor and lumbar spine extensor strength on lumbar spine loading during a squat lift

Weakness of the hip extensors and lumbar spine extensors has been proposed to contribute to greater demands on the lumbar spine during lifting. The purpose of the current study was to examine the associations among strength of the hip and lumbar spine extensors, lumbar spine extensor moments and lumbar paraspinal muscle activation during a squat lift task. Twenty-seven healthy females participated. Strength of the hip and lumbar spine extensors was measured using a dynamometer. Lumbar spine moments and lumbar paraspinal muscle activity were quantified during the concentric phase of the squat lifting task. There was a significant positive association between lumbar extensor strength and average lumbar extensor moment during lifting (r = 0.498, p = 0.008). Similarly, hip extensor strength was positively associated with the average lumbar extension moment (r = 0.382, p = 0.049). Hip extensor strength was negatively associated with activation of the lumbar paraspinal muscles during lifting (ρ = -0.382, p = 0.049). Stronger individuals are more likely to use their hip extensors and lumbar spine extensors to perform a squat lift task. In contrast, those with lower strength employ subtle biomechanical changes to reduce lumbar spine demand.

Accuracy of Robotic-Assisted Spinal Surgery-Comparison to TJR Robotics, da Vinci Robotics, and Optoelectronic Laboratory Robotics

BACKGROUND

The optoelectronic camera source and data interpolation serve as the foundation for navigational integrity in the robotic-assisted surgical platform. The objective of the current systematic review serves to provide a basis for the numerical disparity that exists when comparing the intrinsic accuracy of optoelectronic cameras: accuracy observed in the laboratory setting versus accuracy in the clinical operative environment. It is postulated that there exists a greater number of connections in the optoelectronic kinematic chain when analyzing the clinical operative environment to the laboratory setting. This increase in data interpolation, coupled with intraoperative workflow challenges, reduces the degree of accuracy based on surgical application and to that observed in controlled musculoskeletal kinematic laboratory investigations.

METHODS

Review of the PubMed and Cochrane Library research databases was performed. The exhaustive literature compilation obtained was then vetted to reduce redundancies and categorized into topics of intrinsic optoelectronic accuracy, registration accuracy, musculoskeletal kinematic platforms, and clinical operative platforms.

RESULTS

A total of 147 references make up the basis for the current analysis. Regardless of application, the common denominators affecting overall optoelectronic accuracy are intrinsic accuracy, registration accuracy, and application accuracy. Intrinsic accuracy of optoelectronic tracking equaled or was less than 0.1 mm of translation and 0.1° of rotation per fiducial. Controlled laboratory platforms reported 0.1 to 0.5 mm of translation and 0.1°-1.0° of rotation per array. There is a huge falloff in clinical applications: accuracy in robotic-assisted spinal surgery reported 1.5 to 6.0 mm of translation and 1.5° to 5.0° of rotation when comparing planned to final implant position. Total Joint Robotics and da Vinci urologic robotics computed accuracy, as predicted, lies between these two extremes-1.02 mm for da Vinci and 2 mm for MAKO.

CONCLUSIONS

Navigational integrity and maintenance of fidelity of optoelectronic data is the cornerstone of robotic-assisted spinal surgery. Transitioning from controlled laboratory to clinical operative environments requires an increased number of steps in the optoelectronic kinematic chain and error potential. Diligence in planning, fiducial positioning, system registration, and intraoperative workflow have the potential to improve accuracy and decrease disparity between planned and final implant position. The key determining factors limiting navigation resolution accuracy are highlighted by this Cochrane research analysis.

The biomechanical characteristics of the strongman atlas stone lift

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.

Kinematic and perceptual responses in heavy lifting and pulling: Are there differences between males and females?

This study investigated kinematic and perceptual differences between the sexes in a heavy lifting and pulling task. A 20 kg box was lifted from floor to chest height, and a 70 kg mannequin pulled across 20m. The effect of height, mass and average grip strength on kinematics and perceived workload was examined in 42 (19 females, 23 males) healthy individuals. A univariate linear regression analysis found females lifted with greater lumbar extension compared to males (p < 0.001), and adopted more hip (p = 0.006) and knee flexion (p = 0.036) in the pulling task. Females reported a greater perceived workload in both tasks (p < 0.001). After the multivariable analysis, only grip strength remained significant for perceived workload in the lift (p = 0.04), and height for knee flexion in the pull (p = 0.009). This highlights that height and strength are important factors driving kinematics and perceived workload. Clinicians may consider these factors in heavy manual tasks, more so than sex.

Optimal foot-position of caregiver based on muscle activity of lower back and lower limb while providing sit-to-stand support

[Purpose] In caregivers, low load posture is necessary to prevent lower back pain during patient handling activities such as sit-to-stand support. This study focused on the foot-position of caregivers as an adjustable and useful parameter. A wide stance decreases the stress on the lumbar vertebra. However, this foot-position increases loading of the spinae erector muscles. The aim of this study was to investigate the relationship of anterior-posterior and lateral-medial distances between feet and activity of the spinae erector muscles to determine the optimal foot-position for reducing stress on the lumbar vertebra without increasing spinae erector muscle load. [Participants and Methods] Five young male participants were asked to provide sit-to-stand support 10 times using nine normalized foot-positions with different anterior-posterior and lateral-medial distances. Surface electromyograms of the erector spinae and lower limb muscles were measured during sit-to-stand support. [Results] The results showed that the optimal foot-position (anterior-posterior 55%, lateral-medial 20% of body height) increased muscle activity within the lower limb muscles compared with the lower back muscles and did not increase loads on the erector spinae muscle. [Conclusion] Optimizing foot-position can reduce stress on the lumbar vertebra without increasing load on the spinae erector muscles.

Sex differences in upper limb musculoskeletal biomechanics during a lifting task

Women experience higher prevalence of work-related upper limb musculoskeletal disorders compared to men. Previous studies have investigated the biological, kinematic and electromyographic sex-related differences during a lifting task but the actual differences in musculoskeletal loads remain unknown. We investigated the sex differences in three musculoskeletal indicators: the sum of muscle activations, the sum of muscle forces and the relative time spent beyond a shear-compression dislocation ratio. A musculoskeletal model was scaled on 20 women and 20 men lifting a 6 or 12kg box from hip to eye level. Women generated more muscle forces and activations than men, regardless of the lifted mass. Those differences occurred when the box was above shoulder level. In addition, women might spend more time beyond a shear-compression dislocation ratio. Our work suggests higher musculoskeletal loads among women compared to men during a lifting task, which could be the result of poor technique and strength difference.

Sex-dependent differences in lumbo-pelvic coordination for different lifting tasks: A study on asymptomatic adults

During manual material lifting, the sagittal motion is mainly characterized through the lumbo-pelvic coordination, which is quantified by the ratio between the lumbar and hip rotations (L/P ratio). Alteration in the L/P ratio is an important indicator for low back pain (LBP). Previous studies demonstrated sex-dependent differences in LBP prevalence during lifting activities. However, the sex-dependent differences in the L/P ratio during different lifting tasks has to data not been investigated. An optoelectronic system was used to measure the sagittal lumbo-pelvic motion in 10 males and 10 females. Task A was lifting one weight from the ground in front of the body to three target heights with straight knees (A1-3: abdomen, chest and head levels, respectively). Task B was lifting two identical weights from the ground at the sides of the body to three target angles with bended knees (B1-3: arms close and 45° and 90° abducted to the trunk, respectively). Lifts of 10 kg (males and females) and 20 kg (males only) were performed and three phases were investigated: Phase 1 - pure flexion without load, Phase 2 - lifting up weights, Phase 3 - lowering down weights. Females generally displayed a smaller L/P ratio than males. In Phases 2 and 3, the L/P ratio was greater than in Phase 1 for Tasks A and B. The L/P ratio increased with a greater lifting height for Task B, but displayed no difference neither between lifting 10 kg and 20 kg, nor between weight lifting and lowering for both tasks. These results can provide indications for sex-specific recommendations for safer lifting activities.

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.

Sex differences in upper limb 3D joint contributions during a lifting task

Sex-related differences in work technique may contribute to increasing the risk of musculoskeletal joint disorders among women. In lifting tasks, sex differences have been reported for the trunk and lower limb, although women present a higher prevalence of shoulder disorders. We investigated sex differences in the upper limb technique during a lifting task. Trunk and upper limb kinematics were recorded in 27 women and 27 men lifting a box (6 or 12 kg) from hip to eye level. Work technique was quantified through the three-dimensional contribution of each joint to overall box height. The glenohumeral joint showed a higher contribution in women with a 6 kg box and wrist and elbow joints did with a 12 kg box, compared to men at either 6 or 12 kg. Sex differences occurred systematically above shoulder level. Our results argue for careful consideration of sex during ergonomic intervention, particularly during the overhead task. Practitioner Summary: We investigated the sex-related differences in upper limb technique during lifting tasks. Results highlight a sex-specific kinematic strategy above the shoulder level on the glenohumeral joint and on the wrist and elbow joints. To help reduce women's shoulder disorders in overhead task, ergonomic interventions should account for those differences. Abbreviations: DoF: degree-of-freedom; WR/EL: wrist and elbow; GH: glenohumeral; SC/AC: sternoclavicular and acromioclavicular; TR/PE: pelvo-thoracic.

Grasping an object at floor-level: Is movement strategy a matter of age?

Bending down to pick things up off the floor is something that we do every day. This multisegment task can be done in a considerable number of postural configurations because of the large number of degrees of freedom to be controlled when executing it. In this study where volunteers performed a repetitive bending task, multisegment kinematic analysis allowed us to identify seven different bending strategies. Most operators used more than one bending strategy, but no particular strategy-type was found to be specific for a specific age group. However, the number of strategies used by an operator decreased with increasing age. It therefore appears that this factor influences the variability of the strategies used when repeatedly executing a movement involving the lower limbs to collect small objects from floor-level. This decrease in movement variability in senior operators may contribute to their increased risk of developing musculoskeletal disorders.

Understanding Anthropometric Characteristics Associated With Performance in Manual Lifting Tasks

Beck, B, Middleton, KJ, Billing, DC, Caldwell, JN, and Carstairs, GL. Understanding anthropometric characteristics associated with performance in manual lifting tasks. J Strength Cond Res 33(3): 755-761, 2019-Manual lifting is an essential military job task and is commonly linked to occupational injury. Methods to reduce injury risk focus on ensuring that employees have the requisite physical capacity to safely conduct critical job tasks. The aim of this study was to investigate which anthropometric characteristics are associated with lifting performance to inform targeted training programs for job-critical lifting tasks. Sixty-three (42 men and 21 women) participants conducted 3 maximal lifts to a platform (pack lift to 1.5 m, box lift to 1.3 m and box lift to 1.5 m). A dual-energy x-ray absorptiometry scan was used to quantify anthropometric characteristics (body region-specific lean mass and fat mass). Although anthropometric measures were strongly associated with each other, multivariable linear regression revealed that a significant proportion of the total variation in lifting performance in each of the 3 tasks was explained by upper-arm lean mass (pack lift: β = 5.42, p < 0.001; box lift 1.3 m: β = 5.64, p < 0.001; box lift 1.5 m: β = 7.00, p < 0.001). Leg lean mass also significantly contributed to the variation of pack lift performance (β = 0.93, p = 0.01). When controlling for key anthropometric characteristics in these 3 tasks, separate analyses showed no significant effect of sex or stature on lift performance. These results suggest that the perceived limitations of stature and sex may be overcome by targeted training programs to improve specific physical characteristics associated with lifting performance.

Gender differences in occupations and complaints of musculoskeletal symptoms: Representative sample of South Korean workers

INTRODUCTION

The present study examines gender differences in occupations, occupational hazards, and musculoskeletal symptoms in Korean workers.

METHODS

We performed a secondary analysis of data from the fourth Korean Working Conditions Survey (KWCS).

RESULTS

Relative to "managers," men who were "craft and related trades workers," "equipment, machine operating and assembling workers," and in "elementary occupations" were more likely to report back pain (ORs: 2.08, 2.33, and 2.71, respectively); women who were "skilled agricultural, forestry, and fishery workers" were more likely to report back pain (OR: 3.96). Back pain was more likely to be reported in men exposed to "carrying/moving heavy loads," "painful/tiring postures," and "repetitive hand/arm movements" (ORs: 1.20, 2.26, and 1.28, respectively).

CONCLUSION

Men and women workers differed in their reporting of ergonomic risk factors, and complaints of musculoskeletal symptoms. Am. J. Ind. Med. 60:342-349, 2017. © 2017 Wiley Periodicals, Inc.

Difference between male and female workers lifting the same relative load when palletizing boxes

A few biomechanical studies have contrasted the work techniques of female and male workers during manual material handling (MMH). A recent study showed that female workers differed from males mostly in the strategy they used to lift 15-kg boxes from the ground, especially regarding task duration, knee and back postures and interjoint coordination. However, the lifting technique difference observed in females compared to males was perhaps due to a strength differences. The objective of this study was to test whether female workers would repeat the same lifting technique with a load adjusted to their overall strength (females: 10 kg; males: 15 kg), which can be considered a "relative load" since the overall back strength of females is 2/3 that of males. The task for the participants consisted in transferring boxes from one pallet to another. A dynamic 3D linked segment model was used to estimate the net moments at L5/S1, and different kinematic variables were considered. The results showed that the biomechanics of the lifting techniques used by males and females were similar in terms of task duration and cumulative loading, but different in terms of interjoint coordination pattern. The sequential interjoint coordination pattern previously seen in females with an absolute load (15 kg) was still present with the relative load, suggesting the influence of factors more intrinsically linked to sex. Considering that the female coordination pattern likely stretched posterior passive tissues when lifting boxes from the ground, potentially leading to higher risk of injury, the reason for this sex effect must be identified so that preventive interventions can be proposed.

Ergonomic assessment of airport shuttle driver tasks using an ergonomic analysis toolset

This study aimed to (a) evaluate strength requirements and lower back stresses during lifting and baggage handling tasks with the 3D Static Strength Prediction Program (3DSSPP) and (b) provide additional analyses using rapid entire body assessment (REBA) and the NASA task load index (TLX) to assess the risks associated with the tasks. Four healthy female shuttle drivers of good health aged between 55 and 60 years were observed and interviewed in an effort to determine the tasks required of their occupations. The results indicated that lifting bags and placing them in a shuttle were high risk for injury and possible changes should be further investigated. The study concluded there was a potential for injury associated with baggage storing and retrieval tasks of a shuttle driver.

Sex-based differences in lifting technique under increasing load conditions: A principal component analysis

The objective of the present study was to determine if there is a sex-based difference in lifting technique across increasing-load conditions. Eleven male and 14 female participants (n = 25) with no previous history of low back disorder participated in the study. Participants completed freestyle, symmetric lifts of a box with handles from the floor to a table positioned at 50% of their height for five trials under three load conditions (10%, 20%, and 30% of their individual maximum isometric back strength). Joint kinematic data for the ankle, knee, hip, and lumbar and thoracic spine were collected using a two-camera Optotrak motion capture system. Joint angles were calculated using a three-dimensional Euler rotation sequence. Principal component analysis (PCA) and single component reconstruction were applied to assess differences in lifting technique across the entire waveforms. Thirty-two PCs were retained from the five joints and three axes in accordance with the 90% trace criterion. Repeated-measures ANOVA with a mixed design revealed no significant effect of sex for any of the PCs. This is contrary to previous research that used discrete points on the lifting curve to analyze sex-based differences, but agrees with more recent research using more complex analysis techniques. There was a significant effect of load on lifting technique for five PCs of the lower limb (PC1 of ankle flexion, knee flexion, and knee adduction, as well as PC2 and PC3 of hip flexion) (p < 0.005). However, there was no significant effect of load on the thoracic and lumbar spine. It was concluded that when load is standardized to individual back strength characteristics, males and females adopted a similar lifting technique. In addition, as load increased male and female participants changed their lifting technique in a similar manner.

Sex differences in lifting strategies during a repetitive palletizing task

Forty-five manual material handlers (15 females, 15 expert males and 15 novice males) performed series of box transfers under conditions similar to those of large distribution centers. The objective of the study was to verify whether sex differences in joint motions and in back loading variables (L5/S1 moments) exist during multiple box transfers. The task consisted in transferring 24 15-kg boxes from one pallet to another (4 layers of boxes; 6 boxes/layer: 3 in the front row, 3 in the back) at a self-determined pace and then at an imposed pace of 9 lifts/min. Full-body 3D kinematic data were collected as well as external foot forces. A dynamic 3D linked segment model was used to estimate the net moments at L5/S1. The results show that the peak L5/S1 moment during lifting for females was significantly lower than for males, but once normalized to body size the difference disappeared. In general, the female workers were very close to the posture adopted by the novice males at the instant of the peak resultant moment. However, females were closer to the box than the male workers. One major sex difference was seen when lifting from the ground, with the use of interjoint coordination analyses. Female workers showed a sequential motion initiated by the knees, followed by the hip and the back, while expert males showed a more synchronized motion. The lifting strategy of females likely stretches lumbar spine passive tissues, which in turn put them at greater risk of back injuries. As observed in our previous studies, these differences between expert males, novice males and females are especially notable when the box is lifted from the ground.

Sex differences in the kinematics and neuromuscular control of landing: biological, environmental and sociocultural factors

Potential sex differences in patterns of movement of recreational and competitive athletes were investigated in a systematic review of lower limb kinematics, muscle activation and stiffness during landing and hopping tasks. Little support for sex-specific lower limb kinematic patterns was found in 17 studies retrieved on landing and hopping. Ten studies retrieved on muscle activation during landing provided no support for sex-specific patterns. Four articles retrieved on leg stiffness established that absolute stiffness was lower in females, but differences in stiffness normalized to body mass were less clear. The wider literature indicates that a combination of biological, environmental and sociocultural constraints may shape movement patterns differently in females and males. Sociocultural factors differentially affect accumulated motor experience, practice opportunities and focus of attention in females, leading to differences in motor skill that confound the comparison of female and male movements. The findings of the review support the hypothesis that such sex differences in athletic performance are likely to diminish or disappear with increasing skill. In everyday movement tasks, however, where level of skill is a less meaningful dimension than in sport, differences in movement patterns observed between females and males point instead to the influence of subtle societal expectations on movement patterns.

Interjoint Coordination and the Personal Lift-Assist Device

It has been suggested that interjoint coordination may serve to reduce joint stress and muscular demand and to maintain balance during dynamic lifting tasks, thus having implications for safe lifting practices. Before recommending the use of an on-body ergonomic aid, the Personal Lift-Assist Device (PLAD), it is important to determine any effects this device may have on interjoint coordination. Principal component analyses were applied to relative phase angle waveforms, defining the hip–knee and lumbar spine–hip coordination of 15 males and 15 females during a repetitive lifting task. When wearing the PLAD, users lifted with more synchronous hip–knee and lumbar spine–hip coordination patterns (P< .01). Furthermore, increases in load caused less synchronized interjoint coordination at both the hip–knee and lumbar spine–hip during the up and down phases of the lift (P< .01) for all conditions. No significant main effects of sex or significant interactions were observed on any of the outcome variables.

Two linear regression models predicting cumulative dynamic L5/S1 joint moment during a range of lifting tasks based on static postures

Previous studies have indicated that cumulative L5/S1 joint load is a potential risk factor for low back pain. The assessment of cumulative L5/S1 joint load during a field study is challenging due to the difficulty of continuously monitoring the dynamic joint load. This study proposes two regression models predicting cumulative dynamic L5/S1 joint moment based on the static L5/S1 joint moment of a lifting task at lift-off and set-down and the lift duration. Twelve men performed lifting tasks at varying lifting ranges and asymmetric angles in a laboratory environment. The cumulative L5/S1 joint moment was calculated from continuous dynamic L5/S1 moments as the reference for comparison. The static L5/S1 joint moments at lift-off and set-down were measured for the two regression models. The prediction error of the cumulative L5/S1 joint moment was 21 ± 14 Nm × s (12% of the measured cumulative L5/S1 joint moment) and 14 ± 9 Nm × s (8%) for the first and the second models, respectively. Practitioner Summary: The proposed regression models may provide a practical approach for predicting the cumulative dynamic L5/S1 joint loading of a lifting task for field studies since it requires only the lifting duration and the static moments at the lift-off and/or set-down instants of the lift.

Factors that might give rise to musculoskeletal disorders when mothers lift children in the home

OBJECTIVE

The objective of this research was to identify the risk factors for musculoskeletal disorders present when mothers lift normally developing children weighing between 20 and 31 lbs (9-14 kg) in the home.

METHOD

Twenty five mothers aged 28-40 years completed Sanders and Morse's (2005) self-report survey of pain and high-risk practices. In addition, the OMLITH, a structured checklist for observing mothers lifting children in the home, was developed. Criteria to rate variables relating to the load (child), environment, person (mother) and task as low, moderate or high risk were developed, on the basis of published manual handling assessments. The mothers were observed performing 87 lifts, and risk factors were rated.

RESULTS

The majority of participants reported low back pain (64%). They self-rated bending while carrying a child as most stressful, and various other tasks involving carrying; prolonged bending, squatting or stooping; and lifting a child as physically stressful. At least one risk factor related to the load was recorded in all 87 observations, with moderate to high risk most frequently related to the child's weight (73.6%) or the mother's grip on the child (93.1%). Common environmental factors presenting a moderate to high risk related to space constraints (59.7% of tasks) and equipment (58.6%). Factors related to the mothers' strength and fitness (57.5% of tasks) commonly posed moderate to high risk, as did horizontal reach distances (82.8%), vertical lift distances (78.2%) and reaches above shoulder height or below mid thigh level (88.5%). Trunk rotation greater than 45° or combining rotation and side bending while lifting resulted in a moderate to high risk rating in 72.4% of tasks. The developmental age of the child interacted with weight to increase or decrease the requirement for lifting.

CONCLUSION

Risk factors for musculoskeletal disorders are present to a significant degree, and further research in this area is warranted.

The personal lift-assist device and lifting technique: a principal component analysis

The personal lift-assist device (PLAD) is a non-motorised, on-body device that acts as an external force generator using the concept of stored elastic energy. In this study, the effect of the PLAD on the lifting kinematics of male and female lifters was investigated using principal component analysis. Joint kinematic data of 15 males and 15 females were collected using an opto-electronic system during a freestyle, symmetrical-lifting protocol with and without wearing the PLAD. Of the 31 Principal Components (PCs) retained in the models, eight scores were significantly different between the PLAD and no-PLAD conditions. There were no main effects for gender and no significant interactions. Results indicated that the PLAD similarly affected the lifting kinematics of males and females; demonstrating significantly less lumbar and thoracic flexion and significantly greater hip and ankle flexion when wearing the PLAD. These findings add to the body of work that suggest the PLAD may be a safe and effective ergonomic aid. STATEMENT OF RELEVANCE: The PLAD is an ergonomic aid that has been shown to be effective at reducing low back demands during manual materials handling tasks. This body of work establishes that the PLAD encourages safe lifting practices without adversely affecting lifting technique.

The lumbar and sacrum movement pattern during the back squat exercise

An essential exercise for strength training of the lower limbs is the squat exercise. During this exercise, changes in lumbar lordosis are commonly used to indicate when the descent of the squat should cease, yet the behavior of the lumbar-scarum segments remains unclear. The purpose of this study was to quantify the lumbar-sacrum movements during the back squat, because the movement of the sacrum is influenced by the width of stance, this variable was also investigated. Thirty trained subjects, 18 men with 1 repetition maximum (1RM) squat of 123% (13.9%) of bodyweight and 12 women with 1RM squat of 93% (15.6%), performed a set of narrow and wide stance squats, each carrying an additional 50% of body weight as load. The timing and movement of the lumbar angle (T12/L1), sacrum angle (L5/S1), and lumbar flexion angle (lumbar lordosis) were measured in 3 dimensions for the ascent and decent phases. Men and women achieved similar lumbar angles for both width of stance and phase. Sacrum angles, lumbar flexion angles, and timing differed significantly (p < 0.05) between gender and width of stance. The lumbar flexion range during the descent phase for women in narrow and wide stance was 12.9° and 12.6°, respectively; for men, this range was significantly (p < 0.05) larger at 26.3° and 25.4°, respectively. Men and women developed different movement patterns for the squatting movement, and therefore, this needs to be considered in strength development and screening procedures. The lumbar spine became kyphotic as soon as a load was placed on the shoulders, and any teaching cues to maintain a curved lumbar spine when squatting must be questioned.

How to lift a box that is too large to fit between the knees

Many studies compared lifting techniques such as stoop and squat lifting. Results thus far show that when lifting a wide load, high back loads result, irrespective of the lifting technique applied. This study compared four lifting techniques in 11 male subjects lifting wide loads. One of these techniques, denoted as the weight lifters' technique (WLT), is characterised by a wide foot placement, moderate knee flexion and a straight but not upright trunk. Net moments were calculated with a 3-D linked segment model and spinal forces with an electromyographic-driven trunk model. When lifting the wide box at handles that allow a high grip position, the WLT resulted in over 20% lower compression forces than the free, squat and stoop lifting technique, mainly due to a smaller horizontal distance between the l5S1 joint and the load. When lifting the wide box at the bottom, none of the lifting techniques was clearly superior to the others. STATEMENT OF RELEVANCE: Lifting low-lying and large objects results in high back loads and may therefore result in a high risk of developing low back pain. This study compares the utility of a WLT, in terms of back load and lumbar flexion, to more familiar techniques in these high-risk lifting tasks.

Quantifying the movement and the influence of load in the back squat exercise

The squat is used extensively in strength and conditioning, physical therapy, rehabilitation, and fitness programs. However, the movement pattern of the hip and knee is still relatively unknown, in particular, the timing of when maximum angles is reached. The purpose of this study was to quantify the hip and knee movements of the squat and establish if load alters these movements. Twenty-eight subjects (16 men and 12 women) performed 2 sets of 8 squats. Load was applied in random order as no additional weight (body weight [BW]) or an additional load of 50% of the subject's weight (BW+50%). Joint angles and time for hip and knee, as well as forward knee, displacement in the descent and ascent phases were measured with significance at p<0.05. Regardless of gender, phase, and load, all subjects achieved their maximum hip and knee angles within 2% of the deepest position. Load significantly increased the flexion angle at the hip and knee joints in men. The knees movement forward of the toes ranged from 63.8 to 64.7 mm in men and 93.2 to 96.6 mm in women. A significant difference in the timing of when the maximum forward knee movement occurred was observed because of gender. The overriding factor for the practical prescription of squat technique was regardless of load, gender, or phase; the maximum angles of the hip and knee are reached almost simultaneously at the bottom of the squat. Furthermore, for all subjects, the knee moved forward of the toes when squatting with men reaching their maximum forward knee position around 84% of the descent phase, whereas this occurred for women around 93%.

Can relative strength between the back and knees differentiate lifting strategy?

OBJECTIVE

This study investigated whether relative strength between the back and knees can differentiate and predict lifting strategy and the effects of gender, load magnitude, and knowledge of strength on the strategy.

BACKGROUND

Although muscular strength is thought to play a vital role in the mechanics of lifting, how localized joint strengths and their relations influence lifting strategy remains unclear.

METHOD

Thirty-two participants (16 men and 16 women) underwent isokinetic strength tests and were then divided into two groups: one provided with the knowledge of their strength test results and the other not. They subsequently performed the same set of simulated lifting tasks while their lifting kinematics were being recorded. Postural indices to quantify the lifting strategies were derived from the kinematic data.

RESULTS

The ratio of back strength versus total knee strength and gender had significant effects on measures quantifying the lifting strategy. A statistical model incorporating gender, strength, and anthropometry achieved an R2 value of .64 and predicted correctly 76% of lifting strategies used by individual participants.

CONCLUSION

Individuals with back strength greater than their total knee strength tended to use a back-preferred lift strategy, and vice versa, suggesting that muscular strength is a determining factor of lifting strategy.

APPLICATION

An emphasis on additional knee strengthening in a training program may change the tendency of using and overstressing the back. APPLICATION of modeling and simulation technology for ergonomics design can be enhanced by more individually and accurately specified lifting strategies based on anthropometry and strength profiles.

Effects of educational intervention on joint angles of the trunk and lower extremity and on muscle activities during patient-handling tasks

OBJECTIVE

The objective of this study was to examine the effects of educational intervention on joint angles of the trunk and lower extremity and on muscle activities during patient-handling task.

METHODS

Thirty-two subjects (17 males and 15 females) volunteered for the study. They were classified into three groups: intervention group 1, comprised of first grade physical therapist students; control group, which included first grade occupational therapist students; intervention group 2, which comprised third grade physical therapist students. The educational intervention during the experimental period consisted of: (1) 12 regular classes and short-term clinical practice for the students of intervention group 1; (2) long-term clinical practice, relating to patient-handling task, for the students of intervention group 2. The following experiments were repeated before and after the educational intervention. Each subject was asked to transfer a male (55 kg) from one chair to a second chair (left to right) and then back again to the original chair (right to left). The flexion angles of the trunk, hip and knee joints were quantified by means of the dynamic three-dimensional biomechanical analysis. Muscle activities (% maximum voluntary contraction, %MVC) of biceps brachii, trapezius, rectus femoris and erector spinae muscles were measured using surface electromyography (EMG). The effects of group, gender, measurement time and side on joint angles of trunk and lower extremity, %MVC of four muscle activities and transfer time were assessed.

RESULTS

Although the EMG analysis could not clearly demonstrate any reduction of physical load to the low back, the flexion angles of the hip and knee joints of student subjects during the patient-handling task became larger and that of the trunk became smaller in the group given the educational intervention.

CONCLUSION

The finding of this study suggests that the posture of the study subjects changed to the squat lifting method, which is preferable for reducing the physical load to the lower back, as a result of the educational intervention.

Are female healthcare workers at higher risk of occupational injury?

BACKGROUND

Differential risks of occupational injuries by gender have been examined across various industries. With the number of employees in healthcare rising and an overwhelming proportion of this workforce being female, it is important to address this issue in this growing sector.

AIMS

To determine whether compensated work-related injuries among females are higher than their male colleagues in the British Columbia healthcare sector.

METHODS

Incidents of occupational injury resulting in compensated days lost from work over a 1-year period for all healthcare workers were extracted from a standardized operational database and the numbers of productive hours were obtained from payroll data. Injuries were grouped into all injuries and musculoskeletal injuries (MSIs). Detailed analysis was conducted using Poisson regression modelling.

RESULTS

A total of 42 332 employees were included in the study of whom 11% were male and 89% female. When adjusted for age, occupation, sub-sector, employment category, health region and facility, female workers had significantly higher risk of all injuries [rate ratio (95% CI) = 1.58 (1.24-2.01)] and MSIs [1.43 (1.11-1.85)] compared to their male colleagues.

CONCLUSIONS

Occupational health and safety initiatives should be gender sensitive and developed accordingly.

Low-back loading in lifting two loads beside the body compared to lifting one load in front of the body

Low-back load during manual lifting is considered an important risk factor for the occurrence of low-back pain. Splitting a load, so it can be lifted beside the body (one load in each hand), instead of in front of the body, can be expected to reduce low-back load. Twelve healthy young men lifted 10 and 20-kg wide and narrow loads in front of the body (the single-load lifts). These single-load lifts were compared to a lifting condition in which two 10-kg loads (a total of 20 kg) were lifted beside the body (the split-load lift). Lifts were performed from an initial hand height of 29 cm with four different lifting techniques (stoop, squat, straddle and kneeling techniques). Using measured kinematics, ground reaction forces, and electromyography, low-back loading (3D net moments and spinal forces at the L5/S1 joint) was estimated. Lifting a 20-kg split-load instead of a 20-kg single-load resulted in most cases in a reduction (8-32%) of peak L5/S1 compression forces. The magnitude of the reduction was roughly comparable to halving the load mass and depended on lifting technique and load width. The effects of load-splitting could largely be explained by changes in horizontal distance between the load and L5/S1.

Digital Human Modeling for Workspace Design

Digital human modeling (DHM) technology offers human factors/ergonomics specialists the promise of an efficient means to simulate a large variety of ergonomics issues early in the design of products and manufacturing workstations. It rests on the premise that most products and manufacturing work settings are specified and designed by using sophisticated computer-aided design (CAD) systems. By integrating a computer-rendered avatar (or hominoid) and the CAD-rendered graphics of a prospective workspace, one can simulate issues regarding who can fit, reach, see, manipulate, and so on. In this chapter, I briefly describe the development of various DHM methods to improve CAD systems. Past concerns about early DHM methods are discussed, followed by a description of some of the recent major developments that represent attempts by various groups to address the early concerns. In this latter context, methods are described for using anthropometric databases to ensure that population shape and size are well modeled. Efforts to integrate various biomechanical models into DHM systems also are described, followed by a section that outlines how human motions are being modeled in different DHM systems. In a final section, I discuss recent work to merge cognitive models of human performance with DHM models of manual tasks. Much has been accomplished in recent years to make digital human models more useful and effective in resolving ergonomics issues during the design of products and manufacturing processes, but much remains to be learned and applied in this rapidly evolving aspect of ergonomics.

The effect of floor slope on sub-maximal lifting capacity and technique

Inclined surfaces, where both the lifter and load are on the slope, may be encountered in a jobsite situation. The purpose of this study was to determine if facing up or down a sloped surface (10 degrees and 20 degrees ) would affect maximal acceptable weights of lift (MAWL) using a 10 min psychophysical approach with symmetric freestyle technique at 4 lifts/min. Seventeen healthy men and 18 women determined floor to knuckle height MAWL while facing uphill, downhill, and on a level surface. Motion capture was also performed to examine sagittal plane joint angles and foot placement relative to a milk crate. Slope did not alter MAWL (p>0.05) with the men lifting more than the women in every condition (p<0.001) (25 kg vs. 15 kg, respectively). Foot placement relative to the box was altered by slope such that both horizontal position behind and vertical position below the box increased as slope changed from the downhill to uphill conditions (both p<0.001). Forward torso lean as well as hip, knee, and ankle (plantar) flexion generally decreased as slope changed from the downhill to uphill conditions (all p<0.001). Torso and knee motion appeared to be protected compared to the other joints, changing the least. Though trends were the same in both sexes, interactions did exist in vertical foot position and hip angle (both p0.001). In conclusion, the body is highly adaptive to floor slope, maintaining MAWL at least in the short term. However, while slight technique differences exist between men and women, care should be taken by all when facing uphill due to the tendency to stand further from the load horizontally and when facing downhill due to increased torso lean.

Comparisons of the inter-joint coordination between leading and trailing limbs when crossing obstacles of different heights

Fifteen normal adults walked and crossed obstacles of different heights (10%, 20% and 30% of leg length) with each limb while kinematic data were measured to obtain joint angles in the sagittal plane. Phase angles of each joint were calculated from the angular velocities (x') and displacements (x) as phi=tan(-1)(x'/x). Relative phase angles were then calculated by subtracting phase angles of a distal joint from the proximal joint (phi(hip-knee), phi(knee-ankle)). The standard deviations of the relative phase curve points for the stance and swing phase for each obstacle height were averaged to obtain the respective deviation phase (DP) values. The calculated DP variables were tested using a two-factor repeated ANOVA. The leading and trailing limbs were found to have similar patterns of inter-joint coordination, but different levels of stability, the leading being more stable than the trailing during swing (p<0.05), while only leading knee-ankle coordination was less stable than that of the trailing during stance (p<0.05). Only the stability of the knee-ankle coordination for both limbs decreased with increasing obstacle height during stance (p<0.05). It is suggested that clinical obstacle-crossing training programs for patients with unilateral pathology should include the training of the affected limb, not only as leading but also as trailing limb. An increase of the stability of the ankle joint may be helpful for the stability of the knee-ankle coordination and thus for the general performance of obstacle-crossing.