Biomechanical and metabolic effects of varying backpack loading on simulated marching

Twelve healthy, male Army recruits performed three, 40-min treadmill marches at 6 km/h, under three load carriage conditions: 0%-body weight (BW) backpack load, 15%-BW load and 30%-BW load. Kinematic and kinetic data were obtained, immediately before and after each treadmill march, for computing ankle, knee and hip joint rotations and moments. Metabolic data (oxygen uptake (VO2), expired ventilation (VE), respiratory exchange ratio (RER)), heart rate (HR) and ratings of perceived exertion (RPE) were collected continuously during marching. Significant differences (p < or = 0.05) were observed between each load for VO2, HR and VE throughout the marches. At 40 min, relative energy costs for 0%-BW, 15%-BW and 30%-BW loads were 30, 36 and 41% VO2max, respectively. RPE responses during marching significantly differed for only the 30%-BW load and were greater than responses at 0%-BW and 15%-BW loads. During load carriage trials prior to treadmill marches (pre-march), peaks in internal, hip extension, knee extension and ankle plantar flexion moments increased with increasing backpack load. Relative to 0%-BW load, percentage increases in knee moments, due to 15%-BW and 30%-BW loads, pre-march, were substantially larger than the percentage increases for hip extension and plantar flexion moments, pre-march. Pre-march and post-march peaks in hip extension and ankle plantar flexion moments were similar with all loads, while notable pre-march to post-march declines were observed for knee extension moment peaks, at 15%-BW and 30%-BW load. Pre-march joint loading data suggests that the knee may be effecting substantial compensations during backpack loaded marching, perhaps to attenuate shock or reduce load elsewhere. Post-march kinetic data (particularly at 15%-BW and 30%-BW load), however, indicates that such knee mechanics were not sustained and suggests that excessive knee extensor fatigue may occur prior to march end, even though overall metabolic responses, at 15%-BW and 30%-BW load, remained within generally recommended limits to prevent fatigue during prolonged work.     

Carry-over effects of backpack carriage on trunk posture and repositioning ability

Immediate effects of backpack carriage on spinal curvature and motor control in adults have been reported. However, there is a scarcity of evidence whether the effects would persist or not after the carrying load is removed. This study aimed to investigate the carry-over effects of backpack carriage on trunk posture and repositioning ability. Thirteen healthy adults were recruited and instructed to walk on a treadmill for 30 min with backpack (10% body weight) followed by 30-min unloaded walking. Participant’s trunk posture and repositioning ability were measured at different time points. During backpack carriage, reduction in lumbar lordosis and posterior pelvic tilt with significant increased cervical lordosis, thoracic kyphosis and trunk forward lean were observed. There was also a significant increase in repositioning errors in all spinal curvatures and trunk forward lean. After removal of the carrying load, there was a tendency for restoration of trunk posture and repositioning ability. However, the cervical lordosis and the repositioning error of all spinal curvatures could not be fully returned to the levels of the preload condition (all p < 0.05). The persistent changes in both spinal curvature and repositioning ability revealed an increased risk of spinal injury even after the backpack was removed, and the effects on the neck and back pain warrant future study.

Relevance to Industry

The effects of backpack carriage (10% body weight for 30 min) on the spine could not be fully restored after 30-min unloaded walking. The persistent changes in both spinal curvature and repositioning ability revealed an increased risk of spinal injury even after the backpack was removed. Proper postural reminder might be given to backpack users to alleviate the adverse effects induced after prolonged backpack carriage.     

The effect of wearing high-heels and carrying a backpack on trunk biomechanics

Carrying a bag while wearing high-heels during daily life could potentially cause back pain. No study has investigated the combined effects of wearing a backpack and high-heels on trunk biomechanics from a system-level interaction viewpoint. Consequently, this study aimed to investigate the effects of high-heel height, backpack weight, and habituation in high-heels use on upper body biomechanics. Sixteen female study participants, all in their 20s, were divided into high-heel USER and NON-USER groups, and asked to carry a backpack with 0%, 5% and 10% of their body weight while either not wearing or wearing (0 cm and 9 cm) high-heels. Trunk kinematics and muscle activations were measured under the neutral standing posture while gazing straight ahead in experimental trials. First, the USERS tended to show hyper-lumbar lordosis when wearing high-heels, but the NON-USERS experienced lumbar kyphosis. In line with this, the USERS showed significantly greater recruitment of back muscles (35.5%), but the NON-USERS tended to recruit significantly more abdominal muscles (80%) to control their posture. Second, carrying a backpack sequentially induced posterior pelvic tilting, lumbar kyphosis, and forward head posture which is a stereotype posture of the hyper-kyphotic back and which suggests a system-level interaction from the lower extremity to the head. Third, the backpack weight eliminated the effect of wearing high-heels in the lumbar flexion angle, which may act as a counterbalance to pull the center of gravity (CoG) posteriorly.Relevance to industryCaution must be taken in the long-term use of high-heels and a backpack. Carrying a backpack weighing about 5% of the body weight is recommended to counterbalance the hyper-lordotic lumbar posture when wearing high-heels if unavoidable.     

Effect of load position on physiological and perceptual responses during load carriage with an internal frame backpack

The purpose of this study was to determine the effect of load position in an internal frame backpack on physiological and perceptual variables. Ten female participants walked on a level treadmill for 10?min carrying 25% of their body weight in a high, central, or low position. The variables measured included oxygen consumption (VO₂), heart rate (HR), respiratory exchange ratio (R), respiratory rate (RR), minute ventilation (VE), and rating of perceived exertion (RPE). VO₂, VE, and RPE were significantly lower in the high position (18.6?±?2.3?ml/kg/min, 31.7?±?5.0?l/min, 2.8?±?0.8, respectively) compared to the low position (22.2?±?3.0?ml/kg/min, 38.6?±?7.5?l/min, 3.7?±?1.0, respectively). HR, R, and RR did not change significantly as the load was moved from the high (129.8?±?16.8, 0.89?±?0.06, 30.3?±?4.2, respectively) to the low position (136.0?±?25.3, 0.92?±?0.04, 33.8?±?5.2, respectively). The results of this study suggest that load placement is an important factor in the physiological and perceptual responses to load carriage, and that packing heavy items high in the backpack may be the most energy efficient method of carrying a load on the back.     

The effects of a simulated occupational kneeling exposure on squat mechanics and knee joint load during gait

Occupational kneeling is associated with an increased risk for tibiofemoral knee osteoarthritis. Forces on the knee in the kneeling posture, as well as the greater incidence of meniscus tears among workers, likely contribute to the increased risk. We hypothesise that an additional mechanism may contribute – altered neuromuscular control due to prolonged high knee flexion. Forty participants (20 male, 20 female) completed an evaluation of gait and squatting before, immediately following, and 30 min following a 30 min simulated occupational kneeling exposure. An increase in the peak external knee adduction moment and a delay in vastus medialis activation onset during walking were observed post-kneeling, as well as increased frontal plane knee motion during squatting. This was the first investigation to find changes in high flexion transitions as a result of kneeling. Greater frontal plane knee motion may increase the risk for meniscal tears, and subsequently, knee osteoarthritis.

Practitioner Summary: A 30 min simulated occupational kneeling exposure resulted in small but significant gait changes. The greatest effect was on frontal plane knee movement during squatting, which is especially relevant to occupations requiring frequent kneeling/squatting. This increased motion may indicate an increased risk of injury, which supports a link to knee osteoarthritis.     

ARM处理器的分散加载及特殊应用研究

从ARMELF目标文件主要构成出发,详细介绍了分散加载的基本原理、分散加载文件的语法、分散加载时连接器生成的预定义符号及要重新实现的函数等;以定位目标外设和定义超大型结构体数组两项应用来加以说明,并给出完整的工程实例和Bootloader代码。这些都已经在实际工程中多次应用和验证,是笔者实际工程项目的萃取。     

基于现场总线的硅片自动装卸控制系统设计

开发了一种基于现场总线的硅片自动装卸控制系统。系统采用PROFIBUS-DP总线和ASI总线相结合的控制方式,实现了PECVD石墨舟硅片的装卸过程自动化,提高了太阳能电池片生产线的生产效率和自动化水平,降低了劳动强度,提高了产品质量。     

Cart pushing: The effects of magnitude and direction of the exerted push force, and of trunk inclination on low back loading

The primary objective of the present study was to quantify the relative effect of the magnitude and direction of the exerted push force and of trunk inclination on the mechanical load at the low back using a regression analysis for correlated data. In addition, we explored the effects of handle height and type of pushing activity (standing or walking) on the magnitude and direction of exerted forces, trunk inclination, and low back loading when pushing a four-wheeled cart on a treadmill. An experimental setup was designed in which nine participants pushed a four-wheeled cart on a treadmill. Kinematics and reaction forces on the hand were measured to calculate the net moment at the L5–S1 intervertebral disc. Results show that the magnitude and direction of the exerted push force and the trunk inclination significantly and independently affect low back load. It is concluded that for the ergonomic evaluation of pushing tasks, the inclination of the trunk should be considered, in addition to the magnitude and direction of exerted forces.

Relevance to industry

Pushing carts is a common activity for a considerable part of the workforce and has been associated with musculoskeletal complaints. This paper shows that not only the magnitude of exerted forces determines the low back load but also the direction of the exerted forces and the inclination of the trunk should be considered for ergonomic evaluation.     

Influence of tyre pressure and vertical load on coefficient of rolling resistance and simulated cycling performance

The coefficient of rolling resistance (C _r) for pneumatic tyres is dependent on hysteresis loss from tyre deformation which is affected by the vertical force applied to the tyres (F _v) and the tyre inflation pressure (P _r). The purpose of this paper was to determine the relative influence of five different levels of P _r and four different levels of F _v on C _r and to examine the relationships of C _r with P _r and F _v during cycling locomotion. F _v was modified through carriage of additional mass by the subject. C _r was determined with the coasting deceleration method from measurements performed in a level hallway. Iterations minimizing the sum of the squared difference between the actual deceleration distance and a predicted deceleration distance were used to determine C _r. This latter distance was computed from a derivation based on Newton's second law applied to the forces opposing motion. C _r was described by a hyperbolic function of P _r (C _r = 0.1071 P _r ^?0.477, r ² = 0.99, p &lt; 0.05), decreasing 62.4% from 150 kPa (C_r= 0.0101) to 1200 kPa (C_r = 0.0038). F _v was related to C _r by a polynomial function (C _r = 1.92.10^?8 F _v ² ?2.86.10^?5 F _v + 0.0142, r ² = 0.99, p = 0.084), with an added mass of 15 kg (C _r = 0.0040) resulting in an 11.4% increase in C _r compared with no added mass (C _r = 0.0035). From this study, it is concluded that the relationships of P _r and F _v with C _r for cycling are non-linear. Furthermore, a simulation model shows that changes in P _r and F _v of the magnitude examined here have an important effect on competitive cycling performance.     

Effects of backpack load on critical changes of trunk muscle activation and lumbar spine loading during walking

This study investigated the effects of carrying a backpack while walking. Critical changes featuring the disproportionality of increases in trunk muscle activation and lumbar joint loading between light and heavy backpack carriage weight may reveal the load-bearing strategy (LBS) of the lumbar spine. This was investigated using an integrated system equipped with a motion analysis, a force platform and a wireless surface electromyography (EMG) system to measure the trunk muscle EMG amplitudes and lumbar joint component forces. A predictive goal programming model was developed to determine the most critical changes in trunk muscle activation and lumbar joint loading. Results suggested that lightweight backpack carriage at approximately 3% of body weight (BW) might reduce the peak lumbosacral compression force by 3% during walking compared with no load condition. The most critical changes in both trunk muscle activation and lumbosacral joint loading were found at a backpack load of 10% of BW.

Practitioner Summary: This study investigated the effects of backpack load on the LBS of lumbar spine while walking. A backpack load of 3% of BW might reduce the peak lumbosacral compression force by 3 and 10% of BW induced the most critical changes in LBS of lumbar spine.     

Short-term effects of backpack load placement on spine deformation and repositioning error in schoolchildren

Backpack weight of 10–15% has been recommended as an acceptable limit for schoolchildren. However, there is still no clear guideline regarding where the backpack centre of gravity (CG) should be positioned. The changes of spinal curvature and repositioning error when carrying a backpack loaded at 15% of body weight at different CG locations (anterior or posterior at T7, T12 or L3) in schoolchildren were analysed. Both spinal curvature and repositioning error were found to be affected by backpack anterior–posterior position and CG level. A relatively smaller change was observed during anterior carriage with the least change when the backpack CG was positioned at T12. The results also suggested that alternative carriage by changing the backpack position occasionally between anterior and posterior positions might help to relieve the effects of backpack on spine. However, future study is recommended to further substantiate the beneficial effects of alternative carriage on children.

Statement of Relevance: Anteriorly carried backpack with centre of gravity positioned at T12 was shown to induce relatively less effect on spinal deformation and repositioning error in schoolchildren. Changing backpack carriage position occasionally may help to relieve its effects on spinal deformation. The findings are important for ergonomic schoolbag design and determining a proper load carriage method.     

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.     

Generating pallet loading patterns with considerations of item stacking on end and side surfaces

In late 1979 a two phase heuristic algorithm employing dynamic programming was presented by Steudel for solving the two-dimensional cutting stock problem where all the small rectangles were of the same dimensions, but withour any restrictions that the cutting be performed in a purely “guillotine” fashion. The algorithm was applied to solving the common problem of loading rectangular items of size l by w on a rectangular pallet of size L and W so as to maximize the number of items per layer on the pallet deckboard. In this paper, a new three-phase heuristic is presented which extends the 1979 recursive procedure and evaluates the option of stacking items on their end and/or side surface within the best loading pattern of bottom-stacked items. The resulting pattern is then projected into the third dimension to generate the total “cubic” pallet load. Computation results show that end and/or side stacking (when applicable) can yield average improvements in the range of 5% in items per pallet load.     

The effects of speed,frequency, and load on measured hand forces for a floor to knuckle lifting task

The purpose of this study was to describe and quantify measured hand forces during floor to knuckle lifting of various loads. Hand forces of five subjects were measured with a strain gauge apparatus for normal and fast speeds of lifting at 1,4, and 8 l/min. The pattern of hand force over time exhibited peaks in force in the shape of a spike for all fast lifts, indicating that subjects did not lift smoothly. For normal speed of lift, only one of the five subjects executed some lifts smoothly, indicating that it may be possible to lift smoothly, but most lifters probably do not. Peaks of horizontal and vertical components of hand force were tabulated by speed of lift, frequency, and load.     

The feasibility of repositioning ability as a tool for ergonomic evaluation: effects of chair back inclination and fatigue on head repositioning

Poor posture has been suggested as one of the main factors contributing to the high prevalence of neck pain in video display unit (VDU) users, but no clear association between pain and any particular resting neck posture has been found. Postural awareness of the neck, as indicated by the repositioning accuracy, may therefore be an appropriate measure and potentially useful assessment tool. The objective of this study is to examine whether posture and fatigue affect the head repositioning ability in typical VDU usage.

A group of 20 healthy participants reproduced a normal comfortable posture for forward, upright and backward chair back inclinations in random order both before and after fatigue of the upper trapezius muscles. Ten repetitions of the posture were recorded for 2 s each, and the angular and translational deviations from the original head position were measured with regard to the external environment (head in space repositioning) and with regard to the trunk (head on trunk repositioning). Analysis by repeated measures ANOVA showed significant effects and interactions of fatigue and chair back inclination on the repositioning errors in the sagittal plane, which typically showed systematic trends towards certain postures rather than random errors around a mean position.

While further work is required to examine the ergonomic impact of impaired repositioning ability, head repositioning is sensitive to ergonomic factors such as seating configuration and fatigue, and may therefore be a useful tool for evaluation of static working postures.     

The effects of using a portable music player on simulated driving performance and task-sharing strategies

This study examined the effects of performing scrollable music selection tasks using a portable music player (iPod Touch™) on simulated driving performance and task-sharing strategies, as evidenced through eye glance behaviour and secondary task performance. A total of 37 drivers (18–48 yrs) completed the PC-based MUARC Driver Distraction Test (DDT) while performing music selection tasks on an iPod Touch. Drivers’ eye glance behaviour was examined using faceLAB eye tracking equipment. Results revealed that performing music search tasks while driving increased the amount of time that drivers spent with their eyes off the roadway and decreased their ability to maintain a constant lane position and time headway from a lead vehicle. There was also evidence, however, that drivers attempted to regulate their behaviour when distracted by decreasing their speed and taking a large number of short glances towards the device. Overall, results suggest that performing music search tasks while driving is problematic and steps to prohibit this activity should be taken.     

The effects of a back belt on posture, strength, and spinal compressive force during static lift exertions

The experiment reported in this paper evaluated changes in lifting posture, static lifting strength and the estimated L3/L4 spinal compressive force resulting from the use of an abdominal support or ‘back' belt. Torso posture and maximum static lift strength were measured for eight male and eight female subjects using symmetric and asymmetric hand positions at calf height and elbow height. Body posture, and hand forces were also used as input to a three-dimensional static biomechanical model of the torso used to estimate L3/L4 spinal compressive force. The results showed axial twist of the torso to be significantly lower for calf height asymmetric exertions when the abdominal support belt was worn. The measured reduction in axial twist was approximately four degrees. No other significant effects on posture due to the support belt were found. Static lift strength was not significantly increased or reduced when the support belt was used. Predicted spinal compressive force was significantly lower when a support belt was worn (2840 N compared to 3125 N when the belt was not worn). Overall, the results of the experiment demonstrate a very limited benefit to the user of abdominal support belts, primarily due to reduced or restricted motion during asymmetric and lower-level lifts.Relevance to industryBack belts are commonly used in industry to mitigate manual materials handling hazards. One assumption often made by those recommending the use of back belts is that they substantially reduce the bending and twisting of the torso. The experiment reported in this paper tests this assumption and provides information on the utility of back belts.     

The effects of a passive exoskeleton on muscle activity and metabolic cost of energy

ABSTRACT

Nowadays, low back pain has a high incidence during the crowd who work under a long time and repeated stoop condition. Exoskeletons may form a new strategy to reduce the risk of developing low back pain in stressful jobs. A passive exoskeleton device was introduced in this article to apply to the static maintenance of forward bending work, so as to reduce the load of back muscles when wearers work, which plays the role of prevention and subsequent rehabilitation of low back pain. The hypothesis is that these systems would decrease the severity and number of work-related back injuries, while enhancing workers’ safety. Through a preliminary analysis and a substantial number of experiments, we have demonstrated the feasibility of our approach to substantially decrease the forces and muscle activities at the L5/S1 location during bending. In the static holding experiment, we find lower muscle activity (by 35%～61%) and lower metabolic cost of energy (by 22%) when wearing the exoskeleton. The results demonstrate good potential of this passive exoskeleton to reduce muscle activities at the L5/S1 location and metabolic cost of energy.     

The effects of shoulder posture on neck and shoulder musculoskeletal loading and discomfort during smartphone usage

While using their smartphone, users tend to adopt awkward neck and shoulder postures for an extended duration. Such postures impose the risk of MSDs on those body parts. Numerous studies have been undertaken to examine neck posture; however, few studies have investigated shoulder postures. This study examined various shoulder postures during smartphone use and their effect on neck and shoulder kinematics, muscle loading, and neck/shoulder discomfort. Thirty-two asymptomatic young adult smartphone users randomly performed texting tasks for 3 min at four different shoulder flexion angles (15°, 30°, 45°, and 60°), while maintained a neck posture in the neutral position (0° neck flexion angle). Measures were taken of neck and shoulder muscle activity of the cervical erector spinae (CES), anterior deltoid (AD), upper trapezius (UT) and lower trapezius (LT), and kinematic data (angle, distance and gravitational moment). Results showed AD and LT muscle activity significantly increased when the shoulder flexion angle increased with an opposite effect on CES and UT. A recommended shoulder posture was identified as 30° flexion, as this yielded the best compromise between activation levels of the four muscles studied. This angle also induced the lowest neck/shoulder discomfort score. The findings suggest smartphone users hold their device at approximately 30° shoulder flexion angle with their neck in a neutral posture to reduce the risk of shoulder and neck musculoskeletal disorders when smartphone texting.Relevance to industrySmartphone use in the manufacturing and service industries is an integral part of work and useful means of communication tool. Awkward postures during extensive smartphone use impose an increased risk of both neck and shoulder musculoskeletal disorders. Shoulder flexion angles need consideration when making recommendations about safe work postures during smartphone use.