下村 義弘

The purpose of this study is to analyze the characteristics of deflection of center of foot pressure (CFP) that occurs during a side of center of gravity from the reference, attributed to trunk deflection and muscle force of lower limb. In addition, posture control in the elderly will also be reviewed. The study included 17 healthy elderly subjects and 14 students, adding up to a total of 31 subjects. The subject positioned himself on the force plate and performed an abnormal movement that resulted in a maximum shift of the center of gravity toward the right of the force plate. When the working CFP, acromion, and anterior superior iliac spine (ASIS) moved anteriorly, the deflection (Y-SD) was measured along with the muscle force of lower limb (% body weight). A correlation was sought between each of the above parameters. The results indicated a significant negative correlation between CFP Y-SD and muscle force required for trunk deflection in the elderly group (r=-0.51, p<0.05). In addition, a significant positive correlation was recognized between each of CFP Y-SD, acromion Y-SD, and ASIS Y-SD in the young group (r=0.75, 0.69, p<0.01). Based on the results of the elderly group, it was considered that the muscle force of the tibialis posterior muscle which contributes to the drop of metatarsus and forefoot, and anteroposterior homeostasis contributed to the control of the CFP deflection in the elderly. Thus, it is considered that the factors controlling CFP deflection that occurs during a lateral shift of the center of gravity in the elderly are different from those in the young. The results also suggest different mechanism for maintenance of posture in the two groups.

The purpose of this study was to clarify the strategy of postural control in frontal plane occurred by lateral shifting of center of gravity, and furthermore to reveal related factors of postural strategy in elderly subjects. Healthy 18 elders and 11 young students participated in this study. Subjects achieved the task which was to shift their center of gravity to maximal lateral position. We measured 2-dimensional position of acromion and ante-superior iliac spine (ASIS) in frontal plane. The maximal torques of dorsi / plantar flexion and medial / lateral rotation of ankle were standardized by % body weight (%BW) and used for evaluation of muscler forces of lower leg. According to the results of kinematic measurements of acromion and ASIS, we classified elders in Hip strategy (HS) group (n=13) and Ankle strategy (AS) group (n=5). We employed statistical analysis to compare these HS, AS, and young groups. Result of multi regression analysis of lateral shift of ASIS showed that the significant factors were inferior shift of Acromion for HS (R2=0.638, p<0.01, r=-0.799), and lateral shift of Acromion and plantar flexion torque for young group (R2=0.433, p<0.03, r=0.658). In conclusion, postural strategy with lateral transition of body weight in elders was namely Hip strategy which was controlled with moving mass of pelvic girdle as a counter mass of scapulary movement. However, a part of elderly subjects seemed to have same strategy to young subjects. Therefore studies with multiple view point including sensory system and brain functions will be needed for the future study.

本研究の目的は，足圧中心（CFP）位置を指標とした立位側方不安定位置における高齢者の姿勢制御特性について，CFP動揺特性と下腿筋活動から検討を加えることである。対象は健常高齢群12名と若年群10名とした。設定した課題動作において，CFP全移動距離の80％以上を最大移動区間と定義し，この区間におけるCFP動揺速度標準偏差と下腿筋活動量を2群で比較検討した。下腿筋活動量は高齢群で有意な差は認めなかった。加えて高齢群では，前後方向動揺速度標準偏差と長腓骨筋活動量との間に有意な正の相関関係を認めた（r=0.752, p<0.01）。側方最大移動区間における高齢群の特徴としては，足関節周囲筋群を包括的に収縮させることで足関節の固定を得ていたこと，さらにCFP前後方向の振動の大きさと長腓骨筋活動量に関係があることが見出された。<br>

The purpose of this study was to investigate the effect of the exposure to bright light on EEG activity and subjective sleepiness at rest and at the mental task during nocturnal sleep deprivation. Eight male subjects lay awake in semi-supine in a reclining seat from 21:00 to 04:30 under the bright (BL &gt 25001ux) or the dim (DL &lt 1501ux) light conditions. During the sleep deprivation, the mental task (Stroop color-word conflict test: CWT) was performed each 15min in one hour. EEG, subjective sleepiness, rectal and mean skin temperatures and urinary melatonin concentrations were measured. The subjective sleepiness increased with time of sleep deprivation during both rest and CWT under the DL condition. The exposure to bright light delayed for 2 hours the increase in subjective sleepiness at rest and suppressed the increase in that during CWT. The bright light exposure also delayed the increase in the theta and alpha wave activities in EEG at rest. In contrast, the effect of the bright light exposure on the theta and alpha wave activities disappeared by CWT. Additionally, under the BL condition, the entire theta activity during CWT throughout nocturnal sleep deprivation increased significantly from that in a rest condition. Our results suggest that the exposure to bright light throughout nocturnal sleep deprivation influences the subjective sleepiness during the mental task and the EEG activity, as well as the subjective sleepiness at rest. However, the effect of the bright light exposure on the EEG activity at the mental task diminishes throughout nocturnal sleep deprivation.

The purpose of the present paper is to describe and evaluate the polynomial models for predicting the muscular work capacity of the upper limb during sustained holding tasks. This research was concerned with the relationship between indicators of performance, i.e., specific posture or specific level of maximum voluntary contraction (MVC), and then modeling the functional data based on experimental results to estimate factors that may have an effect on task performance. To this end, we designed an experiment using 10 subjects in which each subject performed sustained isometric shoulder and elbow flexion endurance exercise under 27 conditions [3 shoulder angles (SA)X3 elbow angles (EA)X3 levels of %MVC]. Throughout all experiments, subjective perception of effort was assessed using the Borg scale, every 60, 30, and 10 s during the 20%, 40%, and 60% MVC tests, respectively. Proposal models were represented by three approaches: model A: estimation of endurance time (ET), with input variables such as SA, EA, and %MVC model B: estimation of recommendation time (RT, the time during which the operator was able to maintain a position under the desired condition), with input variables such as SA, EA, %MVC, and required rate on the Borg scale and model C: estimation of limit strength or %MVC, with input variables such as SA, EA, request limit time for work (LT), and required rate on the Borg scale. Statistical analysis indicated that the three proposal estimation models based on polynomial regression functions showed high significance (p&lt 0.0001). The proposal models suggested and recommended the possibility of finding the best positions entailing the reduction and minimization of total muscular strain from manual material handling tasks in different work situations, with the consequent increase in work efficiency.

To investigate the influence of nonthermal factors in the time-of-day effect on the sweating response to maintained static exercise, eight healthy male subjects performed handgrip exercise at 20%, 35% and 50% maximal voluntary contraction (MVC) for 60 s at 0600 hours (morning) and at 1800 hours (evening). Oesophageal temperature (T-oes) before the experiment showed a diurnal rhythm [mean (SEM)] [36.3 (0.1) (morning) compared to 36.8 (0.1) degreesC (evening), P &lt; 0.01]. Experiments were conducted with subjects in a state of mild hyperthermia during which the mean skin temperature (T-sk) was kept constant at 35.5-36.5 degreesC using a water-perfused. suit to activate sudomotor responses. The T-oes and mean T-sk remained stable during the pre-exercise, handgrip exercise and recovery periods. The response in sweating rate (DeltaSR) on the chest and forearm to handgrip exercise increased significantly with increasing exercise intensity in both the morning and evening tests (P &lt; 0.05). The DeltaSR on the palm did not change significantly with increasing exercise intensity in the morning test (P &gt; 0.1). During hand-rip exercise at 50% MVC only, DeltaSR on the chest, forearm and palm in the evening was significantly higher than in the morning (P &lt; 0.05). On the other hand, mean arterial blood pressure and the rating of perceived exertion during 50% WC handgrip exercise were not significantly different between the morning and evening (P &gt; 0.1). These results indicate the presence of a time-of-day effect on nonthermal control of the sweating response to isometric handgrip exercise, and that this effect is dependent on exercise intensity.

To investigate the behavior of mechanomyogram (MMG) and electromyogram (EMG) signals in the time and frequency domains during sustained isometric contraction, MMG and surface EMG were obtained simultaneously from four muscles: upper trapezius (TP), anterior deltoid (DL), biceps brachii (BB), and brachioradialis (BR) of 10 healthy male subjects. Experimental conditions consisted of 27 combinations of 9 postures [3 shoulder angles (SA): 0°, 30°, 60° and 3 elbow angles (EA): 120°, 90°, 60°] and 3 contraction levels: 20%, 40%, and 60% of maximum voluntary contraction (MVC). Subjective evaluations of fatigue were also assessed using the Borg scale at intervals of 60, 30, and 10 sec at 20%, 40%, and 60% MVC tests, respectively. The mean power frequency (MPF) and root mean square (RMS) of both signals were calculated. The current study found clear and significant relationships among physiological and psychological parameters on the one hand and SA and EA on the other. EA's effect on MVC was found to be significant. SA had a highly significant effect on both endurance time and Borg scale. In all experimental conditions, significant correlations were found between the changes in MPF and RMS of EMG in BB with SA and EA (or muscle length). In all four muscles, MMG frequency content was two or three times lower than EMG frequency content. During sustained isometric contraction, the EMG signal showed the well-known shift to lower frequencies (a continuous decrease from onset to completion of the contraction). In contrast, the MMG spectra did not show any shift, although its form changed (generally remaining about constant). Throughout the contraction, increased RMS of EMG was found for all tests, whereas in the MMG signal, a significant progressive increase in RMS was observed only at 20% MVC in all four muscles. This supports the hypothesis that the RMS amplitude of the MMG signal produced during contraction is highly correlated with force production. Possible explanations for this behavioral difference between the MMG and EMG signals are discussed.

The purpose of this study was to evaluate muscle fatigue using electromyogram (EMG) and acoustic myogram (AMG) signals of the shoulder and arm muscles during sustained holding tasks, with the elbow at different angles and at different levels of maximum voluntary contraction (MVC). The EMG and AMG of four muscles, including the upper trapezius (TP), anterior deltoid (DL), biceps brachii (BB), and brachioradialis (BR), were recorded during experiments using 10 healthy young males. The experiments were conducted under 9 pairs of conditions: 3 elbow angles (120°, 90°, and 60°) and * 3 levels of %MVC (20%, 40%, and 60%). Subjects were instructed to hold a weight equal to the designated %MVC at designated joint angles and asked to maintain that condition for as long as possible until exhaustion. Joint angles were also recorded by the electrogoniometers. The analysis of variance revealed that there was no significant effect of elbow angle on the mean MVC or on the endurance time. Elbow angle showed a significant effect on mean power frequency (MPF) of EMG in DL, BB, and BR, and a significant effect on root mean square (RMS) of EMG in four muscles. In BB and BR, MPF of EMG at 120° was found to be significantly lower than 90° and 60°, respectively. There was a significant main effect of elbow angle on MPF of AMG for TP at 20% MVC for DL at 20% and 40% MVC for BB at 40% and 60% MVC and for BR at the three levels of %MVC. The results showed that the range MPF of AMG for DL, BB, and BR was between 32 to 46 Hz, whereas that for TP was from 49 to 83 Hz. There was a significant effect of elbow angle on RMS of AMG in all four muscles in all experiments. At 20% MVC, a progressive increase in RMS of AMG was observed with time. In contrast, at 40% and 60% MVC, RMS showed very different behavior specifically, it was found that RMS of AMG at 20% MVC significantly increased with increase of elbow angle. We conclude that RMS of AMG has a good and clear correlation with elbow angle at a low level of contraction.

It is needed to consider many different situations for designing. We examined vertical work-space for standing posture to propose a comfortable kitchen. In the experiment, 90 points were prepared in 3 sagittal planes including a median sagittal plane. Electromyograms(EMG) and joint angles were recorded during keeping a right hand on each point. After that, subjective ratings of fatigue were obtained. We analyzed these data, and computed mathematical models to adapt different stature. And we proposed a new design of kitchen which had two main fertures; face-to-face and different height of worktop.

Toys that are equipped with the electronic devices and high functional mechanisms are fundamentally designed to run the program with the interruptions of user input or internal / external environmental data basing on the simple autonomic function in itself. Although internal function has got very high ability, present user-interfaces still employ the voice recognizer or simple switches. These present interfaces are categorized as very general and normal method, therefore missing originality. In this viewpoint, we proposed a new interface system for toys using bioelectric signals (especially electromyogram) that method is often used in the field of ergonomics and we made a prototype of bioelectric-controlled robot as a new type of toy.

Although there are many kind of toothbrush handle. the design based on the objective viewpoint is almost nonexistent. In this study, ergonomic methodology including electromyogram and subjective ratings was employed as the evaluation tool of the handle. As a result, optimal thickness of the handle is approximately φ 17.5 mm for the lower part and lO mm at least, 12.5 mm or more for the upper part. The form of crosssection on the upper part is recommended to be nearly circular form and suggested that flat-iike element should be adopted 40 it for more handling stability. The result of this research will become one of an important guideline for designers in future.

The present study attempted to design and evaluate a small portable electromyogram (EMG) amplifier that can output enhanced EMG and its root mean square (RMS) value. The production and design were of a laboratory scale without any special or high cost circuit construction. The designed amplifier was actually innovated according to the actual working conditions based on physiological anthropology. The present amplifier was compared with commercially available products and proved to be of practical use. The device was installed with a sufficiently small body depicting 8-channel variable gain AC amplifier and variable timewindow RMS-to-DC converter. The prototype was battery-driven and well-shielded to minimize external noise interference.

An impotant consideration in cleaning tool design is the reduction of physical fatigue. A bathtub scrubbing hand tool (handle length=40cm, angle=20°, bestowed flexibility on cleaning part) was desinged to reduce physical fatigue. This scrubbing tool was then manufactured and evaluated by measuring electromyogaram and articular angle. This was compared with the one which is on the market, and another which doesn't have a handle. Under similar working conditions, results clearly showed that the designed hand tool reduced physical fatigue.