Atsushi Sugama

BACKGROUND: Manual operations of the hydraulic jack device can become ergonomic stressors for the musculoskeletal system because of the required operational forces, muscle activities, or working postures. However, the usability of the hydraulic jack has not been fully explored for non-professional personnel. OBJECTIVES: To evaluate the musculoskeletal loads during manual operations of a hydraulic jack based on the ergonomic postural analysis and electromyography METHODS: Nine men operated the lever of a hydraulic jack with three positions: parallel to and near (P-N), parallel to and far from (P-F), and orthogonal to the jack lever (O). Postural loads were evaluated by Loading on the Upper Body Assessment (LUBA), an ergonomic observational method, and were classified into action categories. The surface electromyogram of eight muscles and the subjective sense of burden were also measured. RESULTS: The initial force for lever pushing reached 40–80 N and exceeded the recommended forces for the unusual postures. The overall assessment of LUBA showed that 31% of working postures observed in O position require immediate consideration and corrective action and the maximum holding time estimated was < 1 minute. The postural load increased due to the shoulder joint abduction in the P-F and O positions and due to the trunk rotation in O position. CONCLUSIONS: The results suggest that operating the hydraulic jack cause considerable postural loads and manual forces insufficient for several minutes of manual task. Therefore, improving working methods and tool designs are needed to improve usability and decrease the risk of musculoskeletal disorders during jack operations.

Background: Loss of balance is a considerable risk factor for workers while using ladders, because they are required to maintain static postural balance on platforms of a restricted size. This study observed center of mass (CoM) and center of pressure (CoP) behaviors and evaluated the effects of the platform depth (anterior–posterior length) and working postures. Methods: Eleven male participants stood on four platforms with depths ranging from 6 to 15 cm and maintained their positions for 60 s while performing or not performing other tasks (object holding, upward viewing, or both simultaneously). The kinematics were analyzed on the sagittal plane based on the inverse pendulum model. Results: The absolute moving range for the CoP–CoM linearly increased with the decreasing platform depth, and the working postures affected the slopes of the linear fits. The relative range of CoP–CoM displacement on narrow platforms was highly correlated with the subjective sense of instability. Conclusions: Monitoring the CoP is effective for a better understanding and evaluation of static postural balance. This study’s findings contribute to improving the design of work equipment through the use of wider platforms that are robust against the effects of working postures.

This study focuses on work procedure manuals used on construction sites and aims to obtain basic findings related to work procedure manuals that are easy-to-understand for workers, including younger workers. Specifically, work procedure manuals in actual construction sites were analyzed from the perspective of 5W1H, and identified problems through improvement review meetings which included experts of occupational safety. Then, new work procedure manuals for resolving these problems were devised, and also some video-based prototypes which effectively showed the work procedure manuals to workers were created. Furthermore, the proposed work procedure manuals and the video-based prototypes were evaluated by a practitioner in an actual construction site. As the results, it is shown that the proposed work procedure was evaluated overall as easy-to-understand for new workers, although some aspects needed improvement. From the above, we clarified the requirements of work procedure manuals that are easily understandable for new workers.

This study investigates the functional stability limits (FSLs) in the squatting positions. Eleven male participants leaned and moved their pelvis horizontally in the clockwise and counter-clockwise directions while squatting at 11 depth levels. The depth was controlled by changing the hip height from 100% to 0% of the upright position. The FSLs and the center of pressure excursion lengths were calculated from the force-plate data, and the musculoskeletal loads on the lower limbs were estimated from the joint torques and surface electromyograms. As the hip height reduced, the area of the FSLs narrowed by up to 20% of the base of support (BOS) area at the deepest squatting position. The narrowing was affected by the decreasing FSLs in the forward direction, which also decreased by up to 20% of BOS. These quantitative data accurately evaluate the postural stability, suggesting a considerable fall risk during tasks requiring the squatting position.

Falls from heights are the most common causes of occupational fatal accidents in many countries; using agents, such as stepladders or scaffolds, is one of the main causal factor. This study aims to evaluate the postural stability of static standing on narrow platforms. Eleven male participants stood on five platforms that had anterior/posterior widths ranging from 6 to 25 cm and maintained their position for 50 s. The coordinates and velocities of center of mass (CoM) and center of pressure (CoP) were calculated from kinematic data of human body and foot reaction forces. The results showed that the relative position of CoP to the platform width and the translational velocity non-linearly increased with shortened platform width and more significantly changed than the relative position of CoM, while there was no significant difference between the 15-cm and 25-cm platforms. The regression lines of the relative position and the velocity of CoP were approximated as a function of the inverse of the platform width or the square, respectively. Shortened platforms make the postural balance of static standing non-linearly unstable, whereas platforms that are 15 cm or wider stabilize the postural perturbation comparable to that achieved on the ground. Therefore, the equipment with a platform or rungs at least 15 cm or wider should be recommended for tasks at elevated places.

In recent year, the evaluation method of human motion to clarify the usability is needed because it is a hard task to assess the subjective evaluation of usability of product and the comfort of the environment. This study aimed to analyze neck motion using feature extraction with motion division and clarify the relationship between neck motion and workability. We propose the motion division method based on the calculation of probability density function from the Gaussian distribution. The algorithm being proposed uses the analysis of the measured data by an experiment. As part of the experiment, each participant was instructed to gaze at a target while in the sitting posture. The working posture of each participant was measured to evaluate the effects of working velocity on the position of the target. The numbers of extracted feature point decreased with the decreasing working velocity. The normal working velocity condition maximized the number of extracted feature points. Moreover, participants answered the best subjective workability under normal conditions. These results show that increasing the number of extracted feature points may improve workability.

In this study, we sought to develop a system to evaluate the workload of multiple sequential tasks using a digital human and muscle fatigue model, as well as test its validity using a sequential task experiment. The muscle fatigue model is the three-component model introduced by Xia et al. The model assumes that the muscle motor unit consists of resting, activated, and fatigued components. We used a temporal smoothed value of the active component ratio to the non-fatigued component to estimate workload. A system was developed using this model to evaluate workload of any combination of sequential tasks of the single manual handling task. A sequential task consisting of three kinds of material handling task performed by a digital human and real environment was prepared as a validity test. We found that the estimated workload using the simulation and the subjective scores showed a similar pattern with the load of the sequential tasks and repetitions.

The cart-type friction measurement device developed by the authors facilitates measurement of both the static coefficient of friction (SCOF) and the dynamic coefficient of friction (DCOF) between the shoe and the floor simultaneously, as well as measurement with variation in sliding velocity. However, whether slip-resistance evaluation using this cart-type friction measurement device corresponds to the actual slip and fall risks is unclear. To investigate the validity of evaluation of slip resistance between the shoe and the floor by using the SCOF and DCOF values measured with a cart-type friction measurement device, we aimed to investigate the relationship between the slip angle in a ramp test and the coefficient of friction (COF) values between the test safety shoe and the 10 test floor sheets contaminated with a glycerol solution. The results indicate that the SCOF values and the DCOF values corresponding to sliding velocity lower than 0.3 m/s are highly correlated with the slip angle in the ramp test, which suggests that the cart-type friction measurement device can simulate the slip between the shoe and the floor in the ramp test under such sliding velocity conditions. Because the ramp test has been used widely to assess the slip resistance of floors and because the slip angle is highly correlated to the risk of slip-induced falls during level walking, the results suggest that the cart-type friction measurement device is valid and effective for assessing the slip resistance between the shoe and the floor. This study provides new information about the evaluation of slip resistance and indicates that the cart-type friction measurement device will contribute toward the prevention of slip-induced fall accidents.

Background This study examined the relationship between interhandle distances and upper limb exertion during simply pushing and pulling of a cart with four swivel wheels, defined by a roll box pallet (RBP) in a Japanese industrial standard. Methods Six healthy young male participants were asked to push and pull an RBP at a distance of 5.2 m under six conditions corresponding to different interhandle distances (40 cm, 60 cm, and 80 cm) and weights (130 kg and 250 kg). The upper limb exertion was studied by shoulder abduction and flexion, and elbow flexion, as well as surface electromyogram (EMG) in shoulder extensor, and elbow flexor and extensor. Participants were required to provide subjective evaluations on operability after each trial. Results Subjective operability indicated that a narrower interhandle distance had a better operability for pushing. Interhandle distance was also related to upper limb exertion especially for pushing. A narrow interhandle distance caused smaller shoulder adduction but larger elbow flexion. The normalized EMG data revealed that muscular activity became smaller with a narrow interhandle distance in shoulder extensor. During the pulling task, elbow flexion was smaller at a narrow interhandle distance, although subjective operability and normalized EMG were not significantly varied. Conclusion A wider interhandle distance, such as 80 cm, was not suitable in the forwardbackward movement of the RBP. Therefore, this study concluded that an interhandle distance of 40 cm would be suitable for pushing and pulling an RBP to protect the workers’ hands against the risk of injury by installing inner handles.

A roll box pallet (RBP) is manual cargo-handling equipment having four wheels. In occupational environments, some workers have injured their hands while performing transfer tasks using RBPs. The goal of this research was to develop an external attachment that concurrently protects workers' hands and ensures safe RBP operability. In this study the three-dimensional accelerations of RBP movements during rotational transfer tasks were measured and the operability of RBPs was evaluated by the subjective assessment. Six males with three to twenty years of experience in operating RBPs (experienced males) and six males with no experience (inexperienced males) were required to perform the rotational movements of RBPs using two vertical handles. The interhandle distance was adjusted to 40, 50, 60, and 80 cm; for each distance, the loaded weights were varied at 0 and 50 kg. The results exhibited a significant difference in the acceleration patterns between the experienced and inexperienced males. The experienced males exerted higher anterior-posterior acceleration during the initial movement of RBPs, resulting in an operation that was less affected by superimposed weights. Moreover, the experienced males exerted higher lateral acceleration and assessed the operability as preferable at an interhandle distance of 80 cm.

In Japan, a number of fall accidents have been associated with equipment such as stepladders. In this study, industrial accident cases were investigated to understand the incidence of accidents caused by stepladders. A total of 34,195 industrial accidents resulting in at least a 4-day absence from work in 2006 (25.5% of the total industrial accidents) were analyzed based on casualty reports from the Japanese Ministry of Health, Labour and Welfare. Each accident was classified by industry type, accident type, the number of absent days, and victims age, sex, employment period, injury or disease type, and injured or disease-affected part. There were 992 stepladder-related accidents (6 were fatal accidents). The estimated annual number of stepladder-related accidents was 3,896 (24 were fatal accidents, 95% confidence interval [CI]: 3,657–4,135), which accounted for 2.9% of all accidents (95% CI: 2.7–3.1). Based on industry type, 45.5% of the stepladder-related accidents occurred in the construction industry, 15.5% in the manufacturing industry, and 12.3% in the commercial industry. Most of these accidents occurred among >49 years male workers in the construction and manufacturing industries, whereas two-third of these workers in the commercial industry were aged <49 years. A total of 68.6% of the workers sustained a fracture. The most commonly affected body parts were the lower (34.7%) and upper limbs (21.4%), and 64.9% of workers took a leave of absence for >31 days. For 18.4% of workers, the duration of employment at the time of the accident was <1 year; 27.6% of workers were employed for ≥20 years. These results indicate that further research should focus on the conditions that cause these accidents so that prevention strategies can be implemented to reduce the incidence of industrial accidents related to stepladders.

In this study, occupational accident cases in Japan were analyzed to better characterize accidents due to the use of stepladders. The analysis investigated 34,195 occupational accidents that resulted in at least a four-day absence from work in 2006 (25.5% of total occupational accidents), based on casualty reports from the Japanese Ministry of Health, Labour and Welfare. The instances were classified by industry type, accident type, number of absent days, victim's age, gender, employment period, injury/disease type, and injured body part. The results of the analysis revealed that there were 992 accidents (six were fatal) due to stepladders in 2006, representing 2.9% of all accidents that year. The total number of estimated accidents that year was 3,896 (24 were fatal). The results also indicated that individuals who fell from stepladders most frequently suffered from fractures (68.6%) or contusions (16.2%) and that 64.9% of all victims took more than a month's leave of absence. The most common injured parts were the lower limbs (34.7%) and the upper limbs (21.4%). For 18.4% victims, the length of employment with the company they were working for at the time of the accident was one year or less. Most of the accidents occurred while standing on the stepladder (70.4%), whereas 19.4% and 7.9% of the accidents occurred during descending and ascending, respectively. Moreover, out of all the stepladder accidents in 2006, 45.4% occurred in the construction industry, 15.5% in the manufacturing industry, and 12.3% in the commercial industry. The occurrence rate of stepladder accidents in different industries were 7.9% in construction, 4.4% in cleaning, and 3.8% in agriculture and forestry, which were higher than the mean rate (2.9%). This result demonstrates that further research is needed to investigate the working methods with stepladders and their risk evaluation.

We developed a new aramid-fiber white cane that is lightweight, resistant to breakage, and reduces injury caused by the cutting surface. This paper presents the results of evaluating the cane strength and the load on a user's muscles by comparing the new cane (aramid-fiber) with an existing one (carbon-fiber). Six male subjects participated in an experiment analyzing physical load reduction, in which the participants were required to wave a cane for 10 min using only wrist movement in a standing position. The surface electromyogram of five forearm muscles and the mental workload of the upper limb were analyzed. The results indicated that the new aramid-fiber white cane reduced the physical load on the muscles (flexor carpi radialis muscle, extensor carpi radialis muscle, flexor carpi ulnaris muscle, pronator teres muscle) by about 10~40% in comparison with the carbon-fiber white cane. However, the physical load on the extensor carpi ulnaris muscle, which is used during wrist extension, increases by about 30%.

Data for handling forces exerted by individuals during manipulation or assembly tasks are important for calculating the physical load on the body. However, because it is difficult to extract features from force data using conventional waveform analysis methods due to the noisy and nonstationary characteristics of the data, we focused on wavelet transform analysis, which is used to analyze nonstationary signals and pulse waves, and attempted to apply spectral analysis to the handling of force data. The purpose of this study was to develop a new waveform analysis method for handling force data using wavelet transform and demonstrate its effectiveness. First, to discriminate between human handling force components and other components in the data, a wavelet multiresolution analysis was applied to pushing force data obtained by using a push button switch and the human handling force component was extracted. Second, time and phase shifts in feature points such as edges and peaks were compared between the raw and extracted waveforms. The results show that temporal and phase shifts for feature points were sufficiently small, and this method proved superior to the approach of smoothing the handling force waveform. This method makes it possible to find a pattern for handling force exertion and understand its features. © 2013 IEEE.

The purpose of this research is to clarify the influence of the weight of white canes on body load. More specifically, we conducted quantitative evaluations of the load on upper limb muscles when a white cane was manipulated over a long period of time, while the subject remained in a stationary standing position. The white canes used were a new type of white cane newly fabricated using aramid fibers, as well as a conventional type of white cane fabricated using carbon fibers. The results indicated that the newly developed cane reduced the load on the muscles by about 50% in comparison with the conventional type of cane. It became clear that it was possible to sustain the same posture even when used continuously over a long period of time. © 2013 Springer-Verlag.

The present study aimed to investigate the influence of the weight of white canes on upper limb load. Concretely, we conducted quantitative evaluations of the load on upper limb muscles during swinging action of the cane. The white canes used were a new type of white cane newly fabricated using aramid fibers, as well as a conventional type of white cane fabricated using carbon fibers. The results indicated that the newly developed cane reduced the load on the muscles by about 50% in comparison with the conventional type of cane. It became clear that it was possible to sustain the same posture even when used continuously over a long period of time. © Springer-Verlag Berlin Heidelberg 2013.

The purpose of this study was to clarify the work position under a light physical load during an upward-pushing task in the supine position. We quantitatively evaluated the relationship between upper-limb load and work position. Eleven subjects were required to perform a static upward-pushing task with a single hand while elevating their upper limb in the supine position. In all, nine experimental conditions were set up, and three horizontal positions for the pushing portion (ear, shoulder and elbow level) and three heights (60%, 75% and 90% of the upper-limb length) above the ground were selected. Upper-limb loads were evaluated on the basis of joint moment, electromyogram and subjective assessment. The results show that the pushing portion at shoulder level and at a height of 90% of the upper-limb length reduced the upper-limb loads and increased the ease of task performance. Thus, the recommended upper-limb position in the supine position clearly differs from that in the standing position.

During the design phase of industrial products, several attempts are made to use human 3D CAD models for estimating the physical loads exerted from products used and assembled at work. Physical loads are commonly evaluated by biomechanical analyses, which estimate the load on joints and muscles by using data obtained from the working posture and external forces caused by product handling. However, the magnitude and direction of handling forces under certain conditions are not unique because these forces have many degrees of freedom. This causes difficulty in automatically generating handling force data, and it requires us to collect real force data by experiments. The purpose of this study is to develop a database system that contains major types of handling force data and a system that contributes to the reduction in the analysis time for ergonomic evaluation. In this paper, we introduce the basic concept of a force database, a procedure for measuring real force data, and an outline of the user interface of our system.

In field activities such as assembling and packaging workers often use their hands to push down on materials. This type of task requires the worker to expend a relatively great effort, consequently imposing unsafe levels of musculoskeletal load on the upper limbs. The assessment of downward pushing workload is limited due to the difficulty of measuring the internal forces exerted by the worker. Additionally, when the position of the object is changed, the body site experiencing the load may also change because of the alteration in working posture, such as bending of the body trunk and elevating the upper limbs. In the present study, we attempted to quantitatively evaluate the upper limb load during a downward pushing task performed using both hands. We asked 10 subjects to push down on a load-cell plane set vertically at a pressure of 150 N. The following experimental parameters were selected: plane set at three heights (chest, lower back and knee) and three distances between the plane and body trunk (100, 75 and 50% of the forearm length). The pushing force, joint moment, electromyo-gram and subjective assessment were evaluated. The results show that the load on the shoulder and elbow increased with as the height of the load-cell plane increased. Conversely, when the height of the plane was decreased, the lumbar load increased, while the load on the upper limbs decreased. The results of this study provide useful information that may help in improving working postures and formulating work environments that impose less workload.

In field activities performed using a step stool, working postures often involve single-leg lifting. This study focuses on the activities performed using step stools and aims to evaluate the effects of the operational posture on postural stability and lower-limb loads during a step-stool task involving single-leg lifting. Specifically, the task was to move an object with the right hand while the right leg was raised on an upper step. Postural stability was assessed by determining the sway in the center of gravity and the floor reaction force. Lower-limb loads were assessed via electromyograms of eight muscles and a subjective scale. The subjects were 11 male university students. The experimental factors were: the direction in which the task was performed, and the height of the step. The different directions in which the task was performed were the center of the body, left side, and right side. The different step heights used in the study were 30 cm, which is the height of a real step stool, and 5 cm, which was used for examining the results obtained with or without a step. The results show that the posture on the left side is unstable, and the muscle load around the ankle is higher than that at the other sites. Furthermore, the posture at a height of 5 cm is more stable than that at a height of 30 cm. These results show that this study is useful in formulating guidelines for step-stool work ; the guidelines would be based on the nature of the task and the features of the step stool.

In field activities where workers are seated, workers needed to stand up repeatedly to prevent local fatigue. However, there is concern that the act of standing up puts stress on the lower limbs due to the heavy load exerted. Therefore, we consider the installation of a handrail to ease the load on workers. In this study, we focused on physical strain during the act of standing up, and aimed to assess the effect of a low-back chair and the load dispersion effect of a handrail quantitatively. We examined physical strain while ten subjects stood up from chairs with heights of 20 or 40 cm. The experimental factors included two chair heights, three anteroposterior positions of the handrail, and with or without the handrail, for a total of eight conditions. We measured the handrail-manipulation force, the floor reaction force, and performed electromyograms and subjective assessments. The results show that standing up from 20-cm-high chairs increases the strain on workers significantly. In particular, the load on the lower limbs on the opposite side to the handrail were decreased approximately six percent, although load on the upper limbs increased.