Akihiko Seo

Protein kinase C mRNA and protein expressions in hypobaric hypoxia‐induced cardiac hypertrophy in rats

Aim:  Protein kinase C (PKC), cloned as a serine/threonine kinase, plays key roles in diverse intracellular signalling processes and in cardiovascular remodelling during pressure overload or volume overload. We looked for correlations between changes in PKC isoforms (levels and/or subcellular distributions) and cardiac remodelling during experimental hypobaric hypoxic environment (HHE)‐induced pulmonary hypertension.

Osteopontin expression in normal and hypobaric hypoxia-exposed rats.

Aim:  Experimental pulmonary hypertension induced in a hypobaric hypoxic environment (HHE) is characterized by structural remodelling of the heart and pulmonary arteries. Osteopontin (OPN) has emerged as a key factor in cardiovascular remodelling in response to pressure or volume overload. We studied the possible effects of HHE on the OPN synthesis system.

Perceived discomfort functions based on joint moment for various joint motion directions of the upper limb.

The aim of the present study was to formulate the relationship between the perceived discomfort and the joint moment ratio for twelve joint motion directions of the upper limb by considering the between-subject variability, and to investigate the effect of joint motion direction. Three approximation models (i.e., linear, exponential, and logistic function models) were compared in terms of the accuracy of predicting the perceived discomfort, and the logistic function was selected because its average error was lowest. The concept of L-R fuzzy number was used to consider the individual variability of perceived discomfort, and a simplified distribution of perceived discomfort was represented. Cluster analysis showed that the twelve discomfort functions formed two clusters: one for elbow flexion and a second for the remaining joint motions. The data show that elbow flexion is more sensitive than other joint motions to increases in the joint moment ratio.

Proanthocyanidin-rich grape seed extract reduces leg swelling in healthy women during prolonged sitting.

BACKGROUND Leg swelling is a modern-day affliction of sedentary working women. The aim of this study was to evaluate the effectiveness of the intake of grape seed extract (GSE) on leg swelling in healthy Japanese women while sitting. RESULTS Single intake trials and 14 day intake trials were held in a double-blind, placebo-controlled, crossover clinical study. A prolonged sedentary position was maintained for 6 h after GSE or placebo administration. Leg volume distension, increase in body extracellular fluid, and leg water were significantly suppressed in the GSE groups. CONCLUSION The intake of GSE is a contributing factor in the inhibition of leg swelling in healthy women during prolonged sitting.

Evaluation of multiple muscle loads through multi-objective optimization with prediction of subjective satisfaction level: illustration by an application to handrail position for standing.

Proposed here is an evaluation of multiple muscle loads and a procedure for determining optimum solutions to ergonomic design problems. The simultaneous muscle load evaluation is formulated as a multi-objective optimization problem, and optimum solutions are obtained for each participant. In addition, one optimum solution for all participants, which is defined as the compromise solution, is also obtained. Moreover, the proposed method provides both objective and subjective information to support the decision making of designers. The proposed method was applied to the problem of designing the handrail position for the sit-to-stand movement. The height and distance of the handrails were the design variables, and surface electromyograms of four muscles were measured. The optimization results suggest that the proposed evaluation represents the impressions of participants more completely than an independent use of muscle loads. In addition, the compromise solution is determined, and the benefits of the proposed method are examined.

Workload Estimation System of Sequential Manual Tasks by Using Muscle Fatigue Model

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.

Evaluation of Neck Motion Due to Change in Working Velocity Based on Feature Extraction with Motion Division

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.

Static Postural Stability on Narrow Platforms to Prevent Occupational Stepladder Falls

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.

Optimal design method with biomechanical analysis for a work environment reducing physical workload: illustration by application to work table height design

ABSTRACT A work environment should be designed to minimise physical workload. We propose an optimal work environment design method to accomplish this, in which joint moment ratios were calculated by biomechanical analyses through digital human modelling (DHM) and were used to indicate physical workload. The work environment design problem was formulated as a multi-objective optimisation problem, minimising the average and maximum joint moment ratio values to determine the optimal work environment. Sequential approximate optimisation, which improves the accuracy of the response surface by sequentially adding new sampling points from a simulation, was applied to efficiently obtain a precise optimal solution. The proposed method was applied to designing a work table height for light assembly tasks. This method determined the optimal work table height considering the anthropometric diversity of workers from a relatively small number of subjects. Through this case study, the validity of the proposed method is discussed.

Relationship between Weight of Our Developed White Cane and Muscle Load on the Upper Limbs during Swinging Action of the Cane

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.