Influence of carrying heavy loads on soldiers' posture,movements and gait

Military personnel are required to carry heavy loads whilst marching; this load carriage represents a substantial component of training and combat. Studies in the literature mainly concentrate on physiological effects, with few biomechanical studies of military load carriage systems (LCS). This study examines changes in gait and posture caused by increasing load carriage in military LCS. The four conditions used during this study were control (including rifle, boots and helmet carriage, totalling 8 kg), webbing (weighing 8 kg), backpack (24 kg) and a light antitank weapon (LAW; 10 kg), resulting in an incremental increase in load carried from 8, 16, 40 to 50 kg. A total of 20 male soldiers were evaluated in the sagittal plane using a 3-D motion analysis system. Measurements of ankle, knee, femur, trunk and craniovertebral angles and spatiotemporal parameters were made during self-paced walking. Results showed spatiotemporal changes were unrelated to angular changes, perhaps a consequence of military training. Knee and femur ranges of motion (control, 21.1° ± 3.0 and 33.9° ± 7.1 respectively) increased (p < 0.05) with load (LAW, 25.5° ± 2.3 and 37.8° ± 1.5 respectively). The trunk flexed significantly further forward, confirming results from previous studies. In addition, the craniovertebral angle decreased (p < 0.001) indicating a more forward position of the head with load. It is concluded that the head functions in concert with the trunk to counterbalance load. The higher muscular tensions necessary to sustain these changes have been associated with injury, muscle strain and joint problems.     

The reliability of the Extra Load Index as a measure of relative load carriage economy

Abstract

The aim of this study was to measure the reliability of the extra load index (ELI) as a method for assessing relative load carriage economy. Seventeen volunteers (12 males, 5 females) performed walking trials at 3 km·h^?1, 6 km·h^?1 and a self-selected speed. Trial conditions were repeated 7 days later to assess test–retest reliability. Trials involved four 4-minute periods of walking, each separated by 5 min of rest. The initial stage was performed unloaded followed in a randomised order by a second unloaded period and walking with backpacks of 7 and 20 kg. Results show ELI values did not differ significantly between trials for any of the speeds (p = 0.46) with either of the additional loads (p = 0.297). The systematic bias, limits of agreement and coefficients of variation were small in all trial conditions. We conclude the ELI appears to be a reliable measure of relative load carriage economy.

Practitioner Summary: This paper demonstrates that the ELI is a reliable measure of load carriage economy at a range of walking speeds with both a light and heavy load. The ELI, therefore, represents a useful tool for comparing the relative economy associated with different load carriage systems.     

The effects of load placement on the EMG activity of the low back muscles during load carrying by men and women

An electromyographic (EMG) study of the lumbar paraspinal muscles during load carrying was undertaken in a group of 24 healthy subjects, 12 male and 12 female. Two different magnitude loads (10% and 20% of the subject's body weight) and four different carrying positions were compared with walking without an external load. Results indicated changes in back muscle activity showing a significant interaction between load magnitude and carrying position. Compared to walking without an external load, lumbar paraspinal EMG activity showed slight decreases when loads were carried in a backpack position or in the hand ipsilateral to the muscle. EMG activity contralateral to the hand carrying the load was significantly increased. Significant increases occurred when loads were carried anterior to the chest with the arms and a significant difference was found between male and female subjects for this carrying position. These findings have implications for the selection of carrying methods.     

Subjective perceptions of load carriage on the head and back in Xhosa women

The purpose of this study was to compare the subjective perceptual responses to both head-loading and back-loading in a group of Xhosa women. Thirty two women were divided into three groups based on their experience of head-loading and walked on a treadmill on two occasions, head-loading and back-loading, at a self selected walking speed for 4 min with a variety of loads until pain or discomfort caused the test to be terminated or a load of 70% body mass was successfully carried. After each workload there was a 1 min rest period during which the women indicated feelings of pain or discomfort in particular areas of the body via visual analogue scales. At the end of each test the women were asked to complete further questionnaires relating to pain and discomfort and on completion of the second test were also asked to compare the two loading conditions. Finally the women were interviewed to establish their history of load carriage and associated pain and discomfort. The data indicate that whilst back-loading was generally associated with more areas of discomfort than head-loading, the pain and discomfort in the neck associated with head-loading was the predominant factor in the termination of tests and that this was independent of head-loading experience. This early termination meant that, on average, the women could carry greater loads on their backs than on their heads. The study suggests that further work needs to be carried out to establish viable alternatives to head-loading for rural dwellers in Africa.     

Static and dynamic characteristics of the trunk and history of low back pain

A pilot research was undertaken to study the relationship between static and dynamic characteristics of the trunk and the existence of low back pain. Isoinertial dynamic tests were performed using an ISOSTATION B200 dynamometer on 33 non LBP workers and 11 LBP workers. Ranges of motion and isometric strengths were not systematically different between LBP and non LBP, while these differences were significant for the average absolute velocities during dynamics tests against 25 or 50% of the isometric torques. For the mean quadratic velocity during tests against 50% of the isometric torques, a value of 75 degrees per second can be proposed as a threshold for discriminating between LBP and non LBP. The sensitivity and specificity of this test increased to 92 and 88% respectively when the past LBP history was also taken into account. This confirms that trunk velocity during isoinertial movements is very sensitive to low back condition and research should be pursued to identify the biomechanical reasons for this and possibly differentiate between the different symptoms of LBP.     

The effects of backpack type on lumbo-pelvic coordination during trunk bending and return tasks

Abstract

Backpacks with ergonomic features are recommended to mitigate the risk of developing low back pain due to carrying a heavy school backpack. A repeated measure study was conducted on 40 college-age students to investigate the immediate changes in magnitude and timing aspects of lumbo-pelvic coordination when carrying an ergonomically modified vs. a normal backpack relative to no backpack condition during trunk forward bending and backward return tasks. We found a smaller reduction in the thoracic range of rotation, an increase vs. a decrease in pelvic range of rotation and a larger reduction in lumbar flexion for a modified vs. a normal backpack. Furthermore, during the forward bending, a less in-phase motion for the modified backpack was observed. Our results suggest that participants have likely experienced larger spinal loads with the modified backpack; a conclusion that should be investigated in future to determine whether ergonomic backpacks can reduce the risk of low back pain in children.

Practitioner summary: Research participants performed trunk bending and return closer to their habitual way under modified versus normal school backpack. From an equilibrium point of view, therefore, individuals are likely experiencing larger spinal loads during activities of daily living with a modified backpack. However, such a conclusion may change when considering stability requirements.     

Effects of load carriage, load position, and walking speed on energy cost of walking

PURPOSE: The purpose of this study was to examine the effects of load, load position, and walking speed on the energy cost of walking per unit distance (Cw: ml/kg/m). METHODS: Eight young male subjects walked on a treadmill at various speeds with and without load in the hands, on the back, and on the legs. The Cw values were determined from the ratio of 2-min steady-state oxygen consumption (Vo2) above resting value (net Vo2) to the walking speed (v): Cw = net Vo2/v. RESULTS: An energy-saving phenomenon was observed when the load was carried on the back at slower speeds. This phenomenon diminished at faster speeds, particularly when walking faster than 90 m/min. It was also observed when the load was carried in the hands at slower speeds. CONCLUSIONS: These findings partly supported our hypothesis that an energy-saving phenomenon would be observed due to an interaction between rotative torque around the center of body mass and excessive burden on the lower muscles as a function of speed.     

A history of low back pain affects pelvis and trunk mechanics during a sustained lift/lower task

This study compared three-dimensional trunk and pelvis range of motion (ROM) during a sustained asymmetric box lift/lower task between a group with a history of low back pain (HBP, n = 9) and a group with no history of low back pain (NBP, n = 9). Participants lifted an 11-kg box for 10 min at 12 cycles/min from ankle height in front to shelves 45 deg off-centre at waist height. Kinematic data were collected at the beginning (min1), middle (min5) and end of the bout (min9). Two-way analyses of variance were performed for all variables. Pelvis and trunk transverse ROM were similar at min1. By min9, HBP group did not change (31.9 ± 9 deg); however, ROM decreased in NBP group (21.6 ± 6 deg, p < 0.05). Therefore, despite no current pain, the HBP group demonstrated protective lifting mechanics compared to controls. Also discussed are implications for studying lifting paradigms at sub-maximal effort over longer periods of time.

Practitioner summary: Differences between groups over time demonstrate residual consequences of low back pain (LBP) in a manual materials handling scenario. Individuals with a history of LBP (pain free for 6 months) demonstrated more conservative lifting mechanics towards the end of the bout compared to controls with no history of LBP.     

A comparison of trunk biomechanics,musculoskeletal discomfort and productivity during simulated sit-stand office work

Sedentary office work has been shown to cause low back discomfort and potentially cause injury. Prolonged standing work has been shown to cause discomfort. The implementation of a sit–stand paradigm is hypothesised to mitigate discomfort and prevent injury induced by prolonged exposure to each posture in isolation. This study explored the potential of sit–stand to reduce discomfort and prevent injury, without adversely affecting productivity. Twenty-four participants performed simulated office work in three different conditions: sitting, standing and sit–stand. Variables measured included: perceived discomfort, L4–L5 joint loading and typing/mousing productivity. Working in a sit–stand paradigm was found to have the potential to reduce discomfort when compared to working in a sitting or standing only configuration. Sit–stand was found to be associated with reduced lumbar flexion during sitting compared to sitting only. Increasing lumbar flexion during prolonged sitting is a known injury mechanism. Therefore, sit–stand exhibited a potentially beneficial response of reduced lumbar flexion that could have the potential to prevent injury. Sit–stand had no significant effect on productivity.

Practitioner Summary: This study has contributed foundational elements to guide usage recommendations for sit–stand workstations. The sit–stand paradigm can reduce discomfort; however, working in a sit–stand ratio of 15:5 min may not be the most effective ratio. More frequent posture switches may be necessary to realise the full benefit of sit–stand.     

A macro-economic analysis of the effect of offshoring and rehiring on the US economy

Offshore labor outsourcing (“offshoring”) is a process in which US companies set up overseas production facilities, employing local workers, simultaneously curtailing their production on US soil and laying off part of their US workforce. This is followed by (is intertwined with) rehiring a part of the laid-off workers, usually by other companies, to boost production for domestic consumption and/or export. We present a mathematical analysis of the effects of these processes, on such measures as the personal, corporate, government and foreign balances (income minus expenditures). We use an input–output model of the US economy, calibrated to data from government databases, as a reference, and investigate the effects of offshoring and rehiring by mathematical extrapolation. Various rehiring strategies are explored. The analysis is then extended to the effect of cheaper goods and services, arising from splitting the offshoring-generated savings between profit and price reduction. In the latter framework, equilibrium pricing is also investigated.The essence of our findings has been:

1. Primary offshoring results in decreasing (negative) government, personal and foreign balances, and leads to a shifting of private income from payrolls to corporate assets and dividends.

2. Any rehiring is advantageous to the government balance.

3. Rehiring to boost domestic consumption, without profit split, is further decreasing the foreign balance. It also erodes the personal balance because part of the incremental income is offset by taxes and lost social income, and because the growth of personal income is outpaced by the growth of personal consumption.

4. Rehiring to boost exports is advantageous to all three balances but just to break even (pay for the foreign cost of offshoring), the export increment has to exceed, by far, the total foreign payroll.

5. A coordinated expansion to keep the foreign balance in check would be very desirable but requires strong government incentives.

6. Price reduction by profit split obviously improves the personal balance and decreases the corporate profit and balance. The foreign balance may improve, due to a growth of export.

7. When production is increased by rehiring, while maintaining the present ratio between manufacturing and services outputs, equilibrium pricing may only be achieved by decreasing corporate profit and balance as the volume of production grows.

More work is needed to introduce dynamics into the model. An extension of this study would then aim at the analysis of how various taxation and regulatory strategies would affect the offshoring and rehiring process.     

A comparison of low back kinetic estimates obtained through posture matching, rigid link modeling and an EMG-assisted model

This study examined errors introduced by a posture matching approach (3DMatch) relative to dynamic three-dimensional rigid link and EMG-assisted models. Eighty-eight lifting trials of various combinations of heights (floor, 0.67, 1.2 m), asymmetry (left, right and center) and mass (7.6 and 9.7 kg) were videotaped while spine postures, ground reaction forces, segment orientations and muscle activations were documented and used to estimate joint moments and forces (L5/S1). Posture matching over predicted peak and cumulative extension moment (p < 0.0001 for all variables). There was no difference between peak compression estimates obtained with posture matching or EMG-assisted approaches (p = 0.7987). Posture matching over predicted cumulative (p < 0.0001) compressive loading due to a bias in standing, however, individualized bias correction eliminated the differences. Therefore, posture matching provides a method to analyze industrial lifting exposures that will predict kinetic values similar to those of more sophisticated models, provided necessary corrections are applied.     

低碳经济的发展建设推动智能电网

阐述了低碳经济催生下的智能电网发展现状,以及智能电网建设对清洁、可再生能源和节能减排的重要意义。然后本文从电网构架出发分别研究了智能电网发电、输配电、用电环节的低碳发展模式。最后从智能电网技术角度出发讨论了支撑智能电网推动低碳经济发展的关键技术。     

A comparison of simulated annealing and genetic algorithm for optimum design of nonlinear steel space frames

In this article, two algorithms are presented for the optimum design of geometrically nonlinear steel space frames that are based on simulated annealing and genetic algorithm. The design algorithms obtain minimum weight frames by selecting suitable sections from a standard set of steel sections such as the American Institute of Steel Construction (AISC) wide-flange shapes. Stress constraints of AISC Load and Resistance Factor Design (LRFD) and AISC Allowable Stress Design (ASD) specifications, maximum (lateral displacement) and interstorey drift constraints, and also size constraints for columns were imposed on frames. The algorithms were applied to the optimum design of three space frame structures, which have a very small amount of nonlinearity. The unconstrained form of objective function was applied in both optimum design algorithms, and constant penalty factors were used instead of gradually increasing ones. Although genetic algorithm took much less time to converge, the comparisons showed that the simulated annealing algorithm yielded better designs together with AISC-LRFD code specification.     

Eye movement as a mediator of the relationships among time pressure,feedback, and learning performance

The goal of this study is to examine the effects of time pressure and feedback on learning performance, as mediated by eye movement. Time pressure is one of main causes of human error in the workplace. Providing participants with feedback about their performance before task completion has been shown to reduce human error in diverse domains. Since both time pressure and feedback induce motivation, which is closely related to attention, we measured participants' eye movements to trace their attention and information acquisition coupled with a visual display. Time-to-deadline (long and short) and the presence of feedback were the independent factors used while measuring participants’ performance and eye movements as they learned new information about the subject of project management and answered multiple-choice questions via self-paced online learning systems. Using structural equation modeling, we found a mediating effect of eye movement on the relationships among time-to-deadline, feedback, and learning performance. Insufficient time-to-deadline accelerated the number of fixations on the screen, which resulted in longer task completion times and increased correct rates for participants learning about project management. The models in this study suggest the possibility of predicting performance from eye movement under time-to-deadline and feedback conditions. The structural equation model in the study can be applied to online and remote learning systems, in which time management is one of the main challenges for individual learners.     

A cross-sectional study of self-reported back and neck pain among English schoolchildren and associated physical and psychological risk factors

This study set out to identify the associations between ergonomics and other factors with back and neck pain among schoolchildren. Self-reported questionnaires were used to record health outcomes and potential risk factors in state schools. Six hundred and seventy-nine schoolchildren from Surrey in the United Kingdom aged 11–14 years took part. Twenty-seven percent of children reported having neck pain, 18% reported having upper back pain, and 22% reported having low back pain. A forward stepwise logistic regression was performed with pain categories the dependent variables. Neck pain was significantly associated with school furniture features, emotional and conduct problems, family history of low back pain and previous treatment for musculoskeletal disorders. Upper back pain was associated with school bag weight (3.4–4.45 kg), school furniture features, emotional problems and previous treatment for musculoskeletal disorders. Low back pain was associated with school furniture features, emotional problems, family history and previous injury or accident. It is important to recognise the influence of physical, psychological and family factors in children's pain.     

Stand up: comparison of two electrical screed levelling machines to reduce the work demands for the knees and low back among floor layers

Electrical screed levelling machines are developed to reduce kneeling and trunk flexion of sand–cement-bound screed floor layers. An observational intervention study among 10 floor layers was performed to assess the differences between a self-propelled and a manually moved machine. The outcome measures were work demands, production time, perceived load, discomfort and applicability. Compared to the self-propelled machine, the duration of kneeling (?13 min; p = 0.003) and trunk flexion (?12 min; p < 0.001) was shorter using the manually moved machine, and the duration of pushing and pulling increased (?39 min; p < 0.001). No significant or relevant differences were found for production time, perceived load and discomfort. Nine out of ten floor layers found the manually moved machine applicable and three out of ten found the self-propelled machine applicable. When compared with the traditional manner of floor laying, both electrical machines reduced the exposure towards kneeling and trunk flexion.

Practitioner Summary: Electrical machines may help to reduce high physical work demands on floor layers. A manually moved machine is better applicable for the installation of screed floors in residences with smaller floor areas. A self-propelled machine is better applicable on large floor areas with a minimum width of 4 m.     

A comparison of Cobol, Fortran, PL-I and Spitbol

Spitbol, the compiler version of the symbol manipulation language Snobol 4, is compared with the well-known higher-level languages of Cobol, Fortran and PL-I. An algorithm for searching and insertion into a binary tree was chosen for a comparison standard and programmed in each language. Development and computer costs were then compared for the four languages. Although a single comparison does not prove one language superior to another, this comparison does suggest that Spitbol should at least be considered when choosing a programming language for non-numeric applications.     

An investigation of social casino gaming among land-based and Internet gamblers: A comparison of socio-demographic characteristics,gambling and co-morbidities

Social casino games are free-play online games that feature gambling themes, but do not payout winnings in monetary form. These games are distinct from Internet gambling; however, the cross-over between these consumer markets is not well understood. This study compared the use of social casino games among a population of 2010 Australian adult Internet and land-based gamblers who completed a nationally representative telephone survey. The most popular social casino games were poker, gaming machines and casino table games and this popularity differed by gender. Social casino game players were more likely to be younger than non-social casino game players and had more similarities with Internet than land-based gamblers. Internet gamblers were more likely to also play social casino games than land-based gamblers, and use of these games was related to high engagement with gambling. Social casino gamers were more likely to smoke and use illicit drugs, and to have higher levels of psychological distress and gambling problems compared to non-social casino game players. This study is highly significant as it is one of the first comprehensive studies to examine the relationship between social casino game play and gambling in a representative adult population. Consumer protection measures should be strengthened where social casino games are offered in close proximity to gambling and when social casino players are encouraged to migrate to gambling opportunities.     

A field study investigating the effects of a rebar-tying machine on trunk flexion,tool usability and productivity

A field study with a before-and-after experimental design was conducted to evaluate the potential reduction in the risk of musculoskeletal injuries to rodworkers when using an automatic rebar-tying machine. Eleven rodworkers participated in this experiment. All dependent variables (trunk posture, rebar-tying time and responses to a usability questionnaire) were first measured before introducing the rebar-tying machine and then after 3 months of usage all dependent variables were measured again. The results of the study indicated that working with a rebar-tying machine significantly reduced the magnitude, frequency and duration of exposure to awkward trunk posture. Tying time was reduced when participants used the machine. The usability questionnaire indicated that most participants preferred to use the rebar-tying machine for ground-level rebar construction. The field study also revealed that the rebar-tying machine is not limited to the reinforcing trade. The machine can be used for other purposes, such as tying electrical conduit and attaching radiant heat tube to steel mesh. Based on trunk posture exposure, rebar-tying time, usability and transferability, it is concluded that the rebar-tying machine can be an effective tool to reduce the frequency and duration of severe trunk flexion, improve usability and increase productivity among concrete reinforcement workers.     

A performance comparison of current HPC systems: Blue Gene/Q,Cray XE6 and InfiniBand systems

We present here a performance analysis of three of current architectures that have become commonplace in the High Performance Computing world. Blue Gene/Q is the third generation of systems from IBM that use modestly performing cores but at large-scale in order to achieve high performance. The XE6 is the latest in a long line of Cray systems that use a 3-D topology but the first to use its Gemini interconnection network. InfiniBand provides the flexibility of using compute nodes from many vendors that can be connected in many possible topologies. The performance characteristics of each vary vastly, and the way in which nodes are allocated in each type of system can significantly impact on achieved performance. In this work we compare these three systems using a combination of micro-benchmarks and a set of production applications. In addition we also examine the differences in performance variability observed on each system and quantify the lost performance using a combination of both empirical measurements and performance models. Our results show that significant performance can be lost in normal production operation of the Cray XE6 and InfiniBand Clusters in comparison to Blue Gene/Q.