Obesity does not reduce maximum acceptable weights of lift

The effects of handle height, load's CoG height and load on lifting tasks

The effect of the load's center of gravity (CoG) on manual materials handling tasks received little attention in literature. The motivation of this study was to examine the effects of handle height, load's CoG height and load on lifting tasks. Eighteen participants performed 27 lifting tasks, including 3 handle heights (10, 30, 50 cm) by 3 load's CoG heights (10, 30, 50 cm) by 3 loads (7, 14, 21 kg). The lifting time, maximum box tilt angle, muscular activity (brachioradialis, biceps brachii, deltoid, and erector spinae), maximum CoP velocity, and lifting difficulty were measured. The results showed that lifting time and maximum box tilt angle decreased with increasing handle height. Middle handle height (30 cm) resulted in the lowest muscular activity, maximum CoP velocity, and lifting difficulty. Low load's CoG height decreased lifting time, maximum box tilt angle, muscular activity, and lifting difficulty, however, it also increased maximum CoP velocity. In addition, high load increased lifting time, maximum box tilt angle, muscular activity, maximum CoP velocity, and lifting difficulty.

Effects of workers' Body Mass Index and task conditions on exertion psychophysics during Vertical Handling Tasks

BACKGROUND

Obesity prevalence in the workforce is clearly increasing. Simultaneously, manual lifting/lowering loads, referred to as Vertical Handling Tasks (VHT) in this paper, are common in industries and services. Performing VHT exposes workers to physical overload, which can be measured using a psychophysical approach. Various risk factors can increase this overload, including individual factors such as workers' Body Mass Index (BMI).

OBJECTIVE

To study the possible effects of workers' BMI and some task conditions on physical overload during VHT.

METHODS

Psychophysical data were collected from 51 participants having different body constitutions (including non-obese, overweight and obese). The participants performed 6 VHT (3 different loads ×2 workstation configurations), during which they lifted and lowered a test-box between their knees and shoulders. For each task, they reported their perceived exertion using the Borg Category Ratio-10 (CR-10) scale.

RESULTS

The results showed that the CR-10 scale is sensitive to the variation of the task conditions tested. However, the psychophysical data pointed to a tendency to decrease the perception of physical overload as workers' BMI increases.

CONCLUSIONS

This may compromise the validity of the application of psychophysical data as an ergonomic approach for Work-Related Musculoskeletal Disorders (WRMSD) prevention in obese workers.

Plus size and obese workers: anthropometry estimates to promote inclusive design

A significant proportion of the adult population globally is overweight, obese or classed as 'plus size'. This has led to variability in size and shape across the working population and exclusion in the workplace. A new dataset of the anthropometry of plus size people has been created. Length dimensions were similar to other data, but breadth, circumference, and depth measurements were substantially larger. The hip breadth and abdominal depth were important for predicting largeness in this population. These data help explain the high exclusion rates from design and the number of fit, reach, posture and clearance issues reported by participants with a high BMI: generally, the higher the BMI the greater prevalence of problems. It is hoped that a better understanding of the anthropometric characteristics of the plus size worker will inform the design of safe, productive work environments to promote inclusion for a wider range of people. Practitioner Summary: A new anthropometry dataset of plus size people has been created. The higher the BMI the greater the problems with design in the workplace for fit, reach, posture and clearance. To ensure inclusion and reduce stigma it is important to understand more about the size and shape of this population.

Manual patient transfers: factors that influence decisions and kinematic strategies employed by nursing aides

While extensive literature has characterised factors that influence the acceptable mass of 'boxes' during MMH tasks, less is known about these factors when moving 'people' in healthcare settings. This study examined factors that influence decisions/approaches employed during manual patient transfers. Sixteen nursing aides manually-transferred a standardised 'patient'; patient mass was adjusted (using a weight vest) to determine a maximum acceptable patient mass for this task (mass_max). Grip strength was the only worker characteristic significantly associated with mass_max (r = 0.48). Older worker age was associated with smaller peak trunk flexion (r =  -0.58) and shoulder abduction (r =  -0.59), and greater trunk axial twist (r = 0.52). Workers emphasised that patient characteristics (e.g. physical/cognitive status) influenced their decisions when performing transfers. These findings extend previous literature by suggesting that grip strength is a useful predictor of perceived work capacity, older workers adapt protective postural strategies during patient transfers and worker-patient dynamics are crucial during this high-risk occupational task. Practitioner Summary: This study examined manual patient transfers performed by nursing aides. Worker grip strength (but not age or size) was associated with perceptions of maximum acceptable patient mass. Kinematic changes suggested more conservative strategies used by older workers. Workers emphasised that patient characteristics substantially influenced their decisions when performing transfer tasks.

Obesity effects on muscular activity during lifting and lowering tasks

Obesity is an emerging health problem and its incidence has been increasing throughout the workforce. In industrial workstations, vertical handling tasks (VHT), including lifting and lowering, are very common and can cause a significant muscular overload for the involved workers. During these tasks, muscular activity may be considerably affected by workers' body conditions. This study aims to analyze and compare the muscular activity in subjects with different obesity levels, using surface electromyography (EMG), during predefined VHT. Six different VHT (combining 5, 10 and 15-kg loads with two task styles) were performed. EMG data normalization was based on the percentage of maximum contraction during each task (MCT%). The results show that obesity influences the MCT%, which in turn increases the muscular effort during VHT. The current investigation demonstrates that obesity is a relevant musculoskeletal risk factor regarding VHT. The engineering analysis and design implications of this work can thus be perceived.

Biomechanical analysis of manual material handling movement in healthy weight and obese workers

The risk of back injury during work remains high today for manual materials handler. The purpose of this study is to identify the potential presence of compensatory strategies in obese and non-obese handlers and evaluate the impact these strategies have on trunk kinematics and kinetics. The biomechanical and ergonomic impacts in 17 obese and 20 healthy-weight handlers were evaluated. The task studied consisted in moving boxes from a conveyor to a hand trolley and back. The results show that the anthropometric characteristics of obese handlers are linked to a significant increase in peak lumbar loading during lifting and lowering of boxes. Few postural differences between the two groups were observed. These results suggest that the excess weight of an obese worker has a significant added effect on the musculoskeletal structures of the back, which exposes obese handlers to a higher risk of developing a musculoskeletal disorder during load handling.

Central adiposity and mechanical, perceptual and physiological loading during long duration, repetitive lifting

BACKGROUND

There is an absence of information regarding the impact of central adiposity on loading during long duration, repetitive lifting, and very limited information of the impact of elevated body mass on mechanical loading of the lumbar spine. This information is important in evaluation of the validity of injury prevention standards and interventional approaches in this segment of the population.

METHODS

This study evaluated the mechanical, physiological, and perceptual loading during repetitive lifting in participants with central adiposity compared to participants with normal body mass index. Videography, accelerometry, heart rate and perceived exertion measures were used to examine alternations in kinematic, kinetic, and exertional parameters during a 1-hour lifting task (3 × 20-min sets; 4 lifts/min; self-selected mass).

FINDINGS

Low back torque [+69.1 (11.5) Nm], compressive force [+1036.6 (153.6) N] and heart rate [+7.0 (3.5)%] were substantially elevated in participants with central adiposity, however perceived exertion and self-selected mass did not differ between groups. With central adiposity a compensatory mechanism was observed, involving a reduction in trunk vertical displacement [-5.8 (1.9) cm], hip flexion [-6.4 (3.1) deg] and lower-trunk flexion [-10.0 (2.7) deg], which attenuated expected increases to work [9.8 (2.3)%], power [9.5 (4.0)%] and physiological effort.

INTERPRETATION

While mechanical loading increases secondary to elevated body mass are expected, these results provide new insight into origins of such increases for individuals with a central adiposity somatotype. The differences in mechanical, physiological and perceived loading support provision of individual-specific injury prevention strategies, as well as revision of existing mechanical- and physiological-based ergonomic standards.

Use of various obesity measurement and classification methods in occupational safety and health research: a systematic review of the literature

BACKGROUND

This study systematically examined obesity research in occupational safety and health regarding the use of various obesity measurement and classification methods.

METHODS

A systematic search of the PubMed database on English language publications from 2000 to 2015 using related keywords and search of citations resulted in selection of 126 studies. They were categorized into two groups based on their main research question: 1) general physical or mental work-related functioning; and 2) task or body part specific functioning.

RESULTS

Regardless of the study group, body mass index (BMI) was the most frequently used measure. Over 63% of the studies relied solely on BMI to define obesity. In only 22% of the studies, body fat was directly measured by methods such as dual energy x-ray absorptiometry. Abdominal obesity was defined using waist circumference in recent years, and waist-hip ratio in earlier years. Inconsistent cut-offs have also been used across studies investigating similar topics.

CONCLUSIONS

Few authors acknowledged the limitations of using indirect obesity measures. This is in part due to the limited understanding of some occupational safety and health researchers regarding the complex issues surrounding obesity classification and also the mixed recommendations over the past 2-3 decades and across populations. Efforts need to be made to promote appropriate obesity measurement and reporting in this field.

Muscular Power during a Lifting Task Increases after Three Months of Resistance Training in Overweight and Obese Individuals

Background: This study evaluates the effect on power produced during a modified lifting task in the overweight and obese after three months of either resistance or aerobic training. Methods: Seventeen male subjects divided randomly into two groups performed deadlift and deadlift high pull, both with increasing weights up to maximal power, prior to and after the training programs (three sessions per week). Results: Their mean power increased significantly during the deadlift at 20 kg (14.3%, p = 0.026), 30 kg (17.7%, p = 0.008), 40 kg (16.5%, p = 0.011), 50 kg (14.5%, p = 0.020), and 60 kg (14.3%, p = 0.021) and during the deadlift high pull at 30 kg (9.9%, p = 0.037), 40 kg (10.1%, p = 0.035), and 50 kg (8.2%, p = 0.044) after the resistance training. However, the group that participated in the aerobic training failed to show any significant changes in power performance during either the deadlift or deadlift high pull. Conclusion: Three months of resistance training enhances power outputs during a lifting task with weights from 30 to 50 kg (~40–60% of 1-repetition maximum) in the overweight and obese. Because this test was sensitive in revealing pre-post training changes in lifting performance, it should be implemented in the functional diagnostics for overweight and obese individuals and also complement existing testing methods.

Obesity-related changes in prolonged repetitive lifting performance

Despite the rising prevalence of obesity, little is known about its moderating effects on injury risk factors, such as fatigue, in occupational settings. This study investigated the effect of obesity, prolonged repetitive lifting and their interaction on lifting performance of 14 participants, 7 obese (mean body mass index (BMI): 33.2 kg m(-2)) and 7 non-obese (mean BMI: 22.2 kg m(-2)) subjects. To present a physically challenging task, subjects performed repetitive lifting for 1 h at 120% of their maximum acceptable weight of lift. Generalized linear mixed models were fit to posture and acceleration data. The obese group bent to a ∼10° lower peak trunk sagittal flexion angle, had 17% lower root mean square (RMS) jerk and took 0.8 s longer per lift. Over time, the obese group increased their trunk transverse and sagittal posterior accelerations while the non-obese maintained theirs. Although the majority of lifting variables were unaffected by BMI or its interaction with prolonged lifting duration, the observed differences, combined with a greater upper body mass, necessitate a more cautious use of existing psychophysical lifting limits for individuals who are obese, particularly when fatigued.

Influences of Obesity on Job Demands and Worker Capacity

Evidence suggests that the growing prevalence of obesity in the workforce has resulted in an increase in the incidence and cost of musculoskeletal injuries. Obesity can modify job demands and affect worker capacity in terms of anthropometry and occupational biomechanics, which may place workers at greater risk of injury. This paper presents a review of studies quantifying the work-relevant impacts of obesity, specifically related to work task demands, capacities, and their potential imbalance. The increased body fat that accompanies obesity leads to larger anthropometric dimensions and inertial parameters, particularly in the trunk and thigh areas. Consequently, individuals who are obese adjust their work postures and motions as an accommodation. These changes may affect the biomechanical demands on the joints and increase the burden on the musculoskeletal system. Independent of job demands, obesity-related differences also occur with respect to strength, fatigue, and task performance. Directions for future research are provided, focusing on the need for workplace redesign to account for changing workforce demographics.

Biomechanical differences between obese and healthy-weight workers in manual materials handling

The objective of this study was to evaluate the work strategies of obese and healthy-weight workers in manual materials handling. Seventeen obese and 20 healthy-weight manual materials handlers participated in this laboratory study. The tasks consisted of transferring four boxes between a hand trolley and a conveyor. The weight of the box (15 vs. 23 kg), the handling height and the working configuration were modified to see what impact these changes had on the participants’ manual materials handling. Biomechanical measures included net moments, expressed in the pelvic system (flexion–extension, lateral bending and torsion moments), kinematics of body segments and box displacements. The results indicated that trunk and knee postures and horizontal hand distances from L5/S1 were not significantly different between the two groups. Peak moments of force around the transverse, sagittal and longitudinal axes at L5/S1 were 13.3% to 59.0% higher during box lifting and lowering for the obese than for the non-obese workers. The individuals’ body weight explained 57% of the variability in the maximal transverse moments of force at L5/S1 during the lifting of the boxes from the ground. These results suggest that the extra mass of an obese worker causes additional stress for the musculoskeletal structures of the back. These biomechanical differences potentially place obese workers at a greater risk of developing musculoskeletal problems during manual materials handling.

Body shape analyses of large persons in South Korea

Despite the prevalence of obesity and overweight, anthropometric characteristics of large individuals have not been extensively studied. This study investigated body shapes of large persons (Broca index ≥ 20, BMI ≥ 25 or WHR>1.0) using stature-normalised body dimensions data from the latest South Korean anthropometric survey. For each sex, a factor analysis was performed on the anthropometric data set to identify the key factors that explain the shape variability; and then, a cluster analysis was conducted on the factor scores data to determine a set of representative body types. The body types were labelled in terms of their distinct shape characteristics and their relative frequencies were computed for each of the four age groups considered: the 10s, 20s-30s, 40s-50s and 60s. The study findings may facilitate creating artefacts that anthropometrically accommodate large individuals, developing digital human models of large persons and designing future ergonomics studies on largeness.

PRACTITIONER SUMMARY

This study investigated body shapes of large persons using anthropometric data from South Korea. For each sex, multivariate statistical analyses were conducted to identify the key factors of the body shape variability and determine the representative body types. The study findings may facilitate designing artefacts that anthropometrically accommodate large persons.