岩永 光一

Abstract Background There are many conflicting findings on the gaze cueing effect (GCE) of emotional facial expressions. This study aimed to investigate whether an averted gaze, accompanied by a fearful expression of different durations, could enhance attentional orientation, as measured by a participant’s eye movements. Methods Twelve participants (3 females) completed the gaze cue task, reacting to a target location after observing changes in the gaze and expression of a face illustrated on a computer screen. Meanwhile, participants’ eye movements were monitored by electrooculography. The GCE was calculated by reaction time as an indicator of attention shift. Results The analysis of the overall data did not find a significant effect of fearful facial expressions on the GCE. However, analysis of trial data that excluded a participant’s eye movement data showed that brief (0, 100 ms) presentation of the fearful facial expression enhanced the GCE compared to that during a neutral facial expression, although when the presentation time of the fearful expression was increased to 200 or 400 ms, the GCE of the fearful expression was at the same level as when model showed a neutral expression. Conclusions The results suggest that the attention-enhancing effect of gaze cues induced by rapidly presented fearful expressions occurs only when the effect of eye movement trials is excluded. This effect may be mediated by reflexively neural circuits in the amygdala that process threatening stimuli. However, as the expression duration increased, the fearful expression’s attention-enhancing effect decreased. We suggest that future studies on the emotion modulation of GCE should consider the negative effects of participants’ saccades and blinks on the experimental results.

BACKGROUND: The purpose of this study was to clarify the influence of manipulation mode of chopsticks on the learning process, using assessment of task performance and electromyography, and to understand the significance of the traditional manipulation mode from the viewpoint of physiological anthropology. Previous studies have described two modes of manipulating chopsticks, the traditional pincers-pinching mode and the scissors-pinching mode. METHODS: We conducted experiments with two conditions of holding chopsticks: scissors mode and pincers mode. Eight subjects participated and were assigned to these modes, and they learned handling tasks in their assigned mode for 5 days with the non-dominant hand. We measured task execution times and conducted electromyography of the following muscles: first dorsalis interosseus, flexor pollicis brevis, flexor digiti minimi brevis, flexor digitorum superficialis, and extensor digitorum. RESULTS: The training effects were found in each mode. The pincers mode showed significantly shorter task performance times than did scissors mode. On electromyography, significant increases in activity of flexor digiti minimi brevis and tended an increase in flexor digitorum superficialis and a decrease in extensor digitorum occurred in pincers mode but not in scissors mode. CONCLUSIONS: The traditional mode of holding chopsticks was associated with not only high task performance but also an advantage in terms of learning motor control.

Background: Time perception associated with durations from 1 s to several minutes involves activity in the right posterior parietal cortex (rPPC). It is unclear whether altering the activity of the rPPC affects an individual's timing performance. Here, we investigated the human timing performance under the application of transcranial direct-current stimulation (tDCS) that altered the neural activities of the rPPC. Methods: We measured the participants' duration-discrimination threshold by administering a behavioral task during the tDCS application. The tDCS conditions consisted of anodal, cathodal, and sham conditions. The electrodes were placed over the P4 position (10-20 system) and on the left supraorbital forehead. On each task trial, the participant observed two visual stimuli and indicated which was longer. The amount of difference between the two stimulus durations was varied repeatedly throughout the trials according to the participant's responses. The correct answer rate of the trials was calculated for each amount of difference, and the minimum amount with the correct answer rate exceeding 75% was selected as the threshold. The data were analyzed by a linear mixed-effects models procedure. Results: Nineteen volunteers participated in the experiment. We excluded three participants from the analysis: two who reported extreme sleepiness while performing the task and one who could recognize the sham condition correctly with confidence. Our analysis of the 16 participants' data showed that the average value of the thresholds observed under the cathodal condition was lower than that of the sham condition. This suggests that inhibition of the rPPC leads to an improvement in temporal discrimination performance, resulting in improved timing performance. Conclusions: In the present study, we found a new effect that cathodal tDCS over the rPPC enhances temporal discrimination performance. In terms of the existence of anodal/cathodal tDCS effects on human timing performance, the results were consistent with a previous study that investigated temporal reproduction performance during tDCS application. However, the results of the current study further indicated that cathodal tDCS over the rPPC increases accuracy of observed time duration rather than inducing an overestimation as a previous study reported.

BACKGROUND: Sinusoidal lower body negative pressure (SLBNP) has been used to investigate the cardiovascular response to slow periodic changes in blood shifts, but measurements of slow fluctuations take a long time if measured for each period of SLBNP separately. Our study aimed to investigate whether the cardiovascular responses to superimposed SLBNP (S-SLBNP), which is expected to reduce the measurement time, are different from responses measured individually. METHODS: S-SLBNP was configured by superimposing two conventional SLBNPs (C-SLBNP) at 180-s and 30-s periods in the pressure range from 0 to -25 mmHg. As the S-SLBNP has double the static load of C-SLBNP, we also used offset SLBNP (O-SLBNP), which has the same static load level as S-SLBNP. Heart rate (HR), thoracic impedance (Z(0)), and mean arterial pressure (MAP) were measured from 11 male subjects. The transfer functions of gains from MAP to HR (Gain-HR/MAP) and from Z(0) to HR (Gain-HR/Z(0)) were calculated as indexes of arterial baroreflex and cardiopulmonary baroreflex regulation of HR, respectively. RESULTS: The Gain-HR/MAP in the 180-s period (2.11 +/- 0.17 bpm/mmHg; mean +/- SEM) was larger than that of the 30-s period (1.04 +/- 0.09 bpm/mmHg); however, there was no significant difference between the SLBNP conditions. The Gain-HR/Z(0) in C-SLBNP (9.37 +/- 1.47 bpm/ohm) was smaller than that of the other conditions [18.46 +/- 2.45 bpm/ohm (O-SLBNP); 16.09 +/- 2.29 bpm/ohm (S-SLBNP)]. DISCUSSION: Using S-SLBNP could reduce the measurement time needed to examine the arterial baroreflex. However, the cardiopulmonary baroreflex was modified by the static load of SLBNP.

本研究の主な目的は、円滑性追跡眼球運動における速度知覚に動的視対象の視認性による周辺視野の感度が及ぼす影響を調べることであった。追跡タスクの難易度は、以下の刺激特性による視認性で調節された。背景的特性（格子パターンの色構成：白黒対白グレー）と曲線の太さ（0.06deg、0.18deg、0.36deg）が異なる６種類の比較刺激を用いて実験を行った。PC画面上を正弦波の軌跡を描きながら左から右へ移動する比較刺激の先端点の速度を標準刺激よりも｢遅い」または「速い」と感じたかの二者択一による実験から、PSE（主観的等価点） を導出し、分析を行った。結果、円滑性追跡眼球運動の速度知覚は背景である格子パターンの色構成が白とグレーであるときと、正弦波曲線の太さが太いほど有意に速くなることが確認された。これらの結果から、円滑性追跡眼球運動における速度知覚への周辺視野の影響及び周辺視野の速度知覚の変容効果が難易度によって異なることが確認された。

The present study investigated the association of near-infrared spectroscopy (NIRS) signals with systemic hemodynamic changes (SHCs) that can exert confounding effects on brain function analysis. NIRS and SHC parameters - basal thoracic impedance (Z_0), mean arterial pressure (MAP), total peripheral resistance, cardiac output, heart rate and stroke volume - were measured in 13 male subjects. Periodical SHCs were generated using four different periodical changes in sinusoidal lower body negative pressure (12.86, 18, 30 and 90 sec of 0 to -40 mmHg). The frequency response of gain of NIRS signals against Z_0 showed high-pass filter characteristics, however, that of gain against MAP showed low-pass filter characteristics. These results suggest that a compensatory model of NIRS against SHCs needs to consider the frequency characteristics of cardiovascular regulation.

本研究では、円滑性追跡眼球運動（SP眼球運動）時の速度知覚が背景の視覚情報の影響を受けることについて検討した。具体的には、PC画面上を正弦波の軌跡を描きながら左から右へ移動するテスト刺激の先端点の速度を参照刺激よりも「遅い」または「速い」と感じたかの二者択一による実験から、PSEを導出した。背景の視覚情報として、A：1 cycle per degree（cpd）、背景の視覚情報あり、B：0.25cpd、背景の視覚情報あり、a：1cpd、背景の視覚情報なし、b：0.25cpd、背景の視覚情報なしの4条件を設定した。結果、刺激 Bとb において、背景の周期的な特性（0.25cpd）によって速度知覚が遅く感じられたことが確認された。結果から、視覚情報のあり条件では空間周波数0.25cpd条件の方は1cpdより知覚速度が有意に遅くなり、視覚情報のなし条件では、これらの空間周波数条件間に有意な差がないことが示唆された。

The purpose of the present study was to examine how an inserted break influences the cardiovascular and central nervous system responses during periods of mental work. Twelve males conducted two 20-min periods of mental work with a 3-min break between them. Cardiovascular and central nervous system responses were measured continuously. In comparison to the baseline, cardiovascular responses increased continuously even after the inserted break, while, on the contrary, central nervous system activity did not significantly increase during the work periods but relaxed during the break. The work performance increased during the second work period. These results suggest that the inserted break proposed by VDT guidelines in Japan was effective in relaxing the central nervous system but was insufficient to prevent the increase in cardiovascular load. The results also imply that taking rests frequently is important not only to maintaining performance but also to preventing cumulative physiological workloads. © 2013 National Institute of Occupational Safety and Health.

Physiological polytypism can be defined as a human biological trait in which several types of physiological mechanisms account for physical and mental functions, and which results in marked human environmental adaptability based on the whole-body coordination of physiological functions at an individual level. Adaptability (not adaptation) refers to a human functional potentiality that allows humans to adjust to the development of new environments, including technological innovation. A discussion of physiological polytypism is no less than an exploration of the methodology of physiological anthropology.

Background: The purpose of the present study was to compare sinusoidal versus constant lower body negative pressure (LBNP) with reference to very mild whole-body heating. Sinusoidal LBNP has a periodic load component (PLC) and a constant load component (CLC) of orthostatic stress, whereas constant LBNP has only a CLC. We tested two sinusoidal patterns (30-s and 180-s periods with 25 mmHg amplitude) of LBNP and a constant LBNP with -25 mmHg in 12 adult male subjects. Results: Although the CLC of all three LBNP conditions were configured with -25 mmHg, the mean arterial pressure (MAP) results showed a significantly large decrease from baseline in the 30-s period condition (P <0.01). In contrast, the other cardiovascular indices (heart rate (HR), stroke volume (SV), cardiac output (CO), basal thoracic impedance (Z(0)), total peripheral resistance (TPR), the natural logarithmic of the HF component (lnHF), and LF/HF (ln (LF/HF))) of heart rate variability (HRV) showed relatively small variations from baseline in the 30-s period condition (P <0.01). The result of the gain and phase of transfer function at the sinusoidal period of LBNP showed that the very mild whole-body heating augmented the orthostatic responses. Conclusion: These results revealed that the effect of the CLC of LBNP on cardiovascular adjustability was attenuated by the addition of the PLC to LBNP. Based on the results of suppressed HRV response from baseline in the 30-s period condition, we suggest that the attenuation may be caused by the suppression of the vagal responsiveness to LBNP.

The prediction method of melatonin suppression values was based on previous studies related to melatonin suppression and pupil constriction. Estimated values that considered pupil constriction were larger than the actual suppression values. We focused on the pupil constriction and its correction factor to interpret the action spectrum for the properties of the melatonin suppression model. When the correction factor was used to modify the model, actual suppression values were almost completely predictable. These factors suggest that it might be possible to explain the indescribable results.

The purpose of the present study was to compare the physiological responses to different types of mental stress encountered in the workplace. Circulatory and central nervous system responses were examined in 8 healthy males by exposing them to 20-min of white noise (80 dB(A)) and 20-min of computer-based mental arithmetic tasks as models of vascular and cardiac stress, respectively. The results indicated that both cardiac and vascular stresses increased blood pressure and showed a cumulative effect as exposure period was extended. Heart rate and prefrontal oxygenated hemoglobin levels (measured by NIRS) increased in the face of cardiac stress but were not clearly altered by vascular stress and indicated that cardiac stress higher cardiac response and requires more oxygen supply to the brain. As the central nervous system responded, an event-related potential P300 component was elicited by an auditory oddball task presented before and after each stress. The P300 amplitude increased for both stresses. However, P300 latency increased in response to cardiac stress but decreased with vascular stress in the left prefrontal. Thus, the circulatory and central nervous system responses to cardiac stress and to vascular stress may have different underlying mechanisms, and measuring physiological indices appears to be an effective method by which to evaluate the influence of mental stress.

ウェブサイトのロード時等における待ち時間は、たとえ数秒程度であっても、ユーザに不快感を与える一要素である。従って、この不快感を軽減するようなGUIは、ユーザの満足度の向上に繋がると考えられる。そこで、本研究では、ユーザに待ち時間をより短く感じさせるようなGUIの基本特性を明らかにし、ウェブサイトへの応用を提案することを目的とした。具体的には、待ち時間を告知するGUIに含まれる基礎的かつ汎用的特性として、動的な変化の有無と待ち時間終了時の予測可能性に焦点を当て、これらの特性によってユーザの時間感覚が変化するか否か、変化するとすればどのように変化するのかを、実験的に検討した。また、数秒程度という短時間の時間感覚に対して、ユーザ自身が量的な評価を与えることは難しいことを踏まえ、ユーザによる質的な回答から物理的時間と主観的時間の関連性を見出すべく、主観的等価点(PSE)の概念を分析プロセスに導入した。結果から、GUIの特性によってユーザの時間感覚が変容することを示し、特に2秒程度の待ち時間をより短く感じさせるGUIの特性として、待ち時間終了時が予測不可能な動的反復のパターンを明らかにした。

The prediction method of melatonin suppression values was based on previous studies related to melatonin suppression and pupil constriction. Estimated values that considered pupil constriction were larger than the actual suppression values. We focused on the pupil constriction and its correction factor to interpret the action spectrum for the properties of the melatonin suppression model. When the correction factor was used to modify the model, actual suppression values were almost completely predictable. These factors suggest that it might be possible to explain the indescribable results.

We examined the effects of eating a meal on the physiological responses during the performance of a mental task. Ten male subjects (25±4.5 years) participated in this study. We measured the following items: electrocardiogram (ECG), photoplethysmogram (PTG), baroreflex sensitivity (BRS), salivary-amylase activity levels, NASA task load index (NASA-TLX), reaction time and correct rate of the mental task. All experiments were conducted at the same time of day on separate days under two lunchtime conditions, which were taking a meal (meal condition) and not taking a meal (no meal condition) during the lunchtime. The mental tasks were performed before and after the lunchtime. We analyzed the collected data using a paired t-test. The task performance and subjective evaluation (NASA-TLX) showed no significant difference between meal and no meal conditions. On the other hand, heart rate, pulse wave transit time and BRS were significantly different between meal and no meal conditions. The heart rate during the meal condition was significantly (p<0.01) higher than that during the no meal condition. Pulse wave transit time and BRS during the meal condition were significantly lower than those during the no meal condition. The results suggested that eating a meal effectively increases activity level of physiological functions during the performance of a mental task, especially in the cardiovascular system.

This study aimed to investigate the relationship between the muscular strength of the lower extremity in a load side and the characteristics of center of foot pressure (COP) during landing after crossover stepping in the elderly. The study population comprised 8 elderly subjects (average age, 75.8+/-8.0 years) and 9 young individuals (average age, 21.6+/-2.5 years). Using a separation-type force plate, we measured the deflection characteristics of the COP; these were defined by the root mean square of positional change (COP-RMS) and the deflection velocity of the COP (COP-Vel) during landing after crossover stepping. Furthermore, we measured the muscular strength of the lower extremity by using a hand-held dynamometer. By using multiple regression analysis, we detected the calculated muscular strength as the independent variable of the deflection characteristics of the COP. Compared to the young group the elderly group showed significantly higher anterior-posterior COP-RMS values (p<0.05) and lower lateral COP-Vel values (p<0.001). In the elderly, the muscular strengths of the tibialis anterior and adductor magnus were detected as a significant independent variable of the anterior-posterior COP-RMS (R(2)=0.85, R(2)=0.76, p<0.01) and lateral COP-Vel (R(2)=0.75, R(2)=0.65, p<0.05), respectively. With regard to the COP deflection characteristics during landing after crossover stepping in the elderly, we recognized the diagnostic character of the anterior-posterior COP-RMS and lateral COP-Vel. Furthermore, it was suggested that the muscular strengths of the tibialis anterior and adductor magnus played a role in regulating the COP deflection characteristics.

A specially designed mental task was performed by 16 subjects for frequency domain analysis of skin conductance (SC) to evaluate mental workload. The task was to memorize target letters, detect them within a 4×4 alphabet arrangement, and answer whether the number of targets contained in the arrangement corresponded to a randomly displayed number. As the number of target letters increased, the score for the card-sort NASA Task Load Index (CSTLX) and task performance increased significantly. The traditional parameter for the number of transient wave forms of SC response (SCR) and the height of its wave did not show any significant effect of task difficulty. In addition, SCRs were subjected to Fourier transformation and integration of the spectrum from 0.03 to 0.5 Hz. This frequency domain analysis enabled detection of small differences in mental workload that could not be detected by traditional amplitude domain analysis. Frequency-based analysis enables easy processing of physiological signals and is very effective in evaluating mental stress using SC recorded under actual environmental conditions such as the driving of a vehicle.

The purpose of this study was to investigate the influence of the force tremor (FT) on mechanomyographic (MMG) signals recorded by a condenser microphone (MIC) and an accelerometer (ACC) during measurement of agonist and antagonist muscles in sustained isometric contractions. Surface electromyographic (EMG) signals and MMG signals by MIC (MMG-_<MIC>) and ACC (MMG-_<ACC>) were recorded simultaneously on biceps brachii (BB) and triceps brachii (TB). Following determination of the isometric maximum voluntary contraction (MVC), 10 male subjects were asked to perform sustained elbow flexion and extension contractions at 30% MVC until exhaustion. We analyzed the root mean square (RMS) for all signals and compared the sum of the power spectrum (SPA) for 3-6 Hz and 8-12 Hz and the ratio of the sum of SPA for 3-6 Hz and 8-12 Hz in SPA for 3-100 Hz (SPA-_<FT>/SPA-_<3-100Hz>) between MMG-_<MIC> and MMG-_<ACC>. During all sustained muscle contractions, the RMS of EMG and MMG-_<MIC> was significantly (p<0.05) increased in antagonistic muscle pairs, while the increase was more noticeable for the agonist than for the antagonist. In addition, the antagonist had a significantly (p<0.05) smaller amplitude than the agonist muscle. The RMS of MMG-_<ACC>, however, showed no significant (p>0.05) difference in RMS amplitude and slope between agonist and antagonist muscles during flexion. In extension, the MMG-_<ACC>-RMS amplitude showed a tendency to be higher in the antagonist than in the agonist, while their slopes showed no significant (p>0.05) difference. The SPA for 3-6 Hz and 8-12 Hz in MMG-_<MIC> showed a tendency to be higher in the agonist than the antagonist, and the slopes of the agonist were significantly (p<0.05) higher than those of the antagonist in all contractions. In MMG-_<ACC>, SPA and slopes for 3-6 Hz and 8-12 Hz tended not to differ between agonist and antagonist. The SPA-_<FT>/SPA-_<3-100Hz> in MMG-_<ACC> showed that the antagonist was higher than that of the agonist in all contractions. The MMG-_<MIC>, however, showed a tendency toward no difference between the agonist and antagonist. In the assessment of muscle activity during simultaneous measurement of the agonist and antagonist during sustained muscle contractions, the MMG signal detected by MIC appeared to be less affected by FT than by ACC due to the different inherent characteristics of the two transducers.

The effects of various heel elevations on postural adjustment and lower-extremity muscle activity during the squat-to-stand (SQ-ST) movement were investigated. Eight healthy mate subjects participated in the experiment, which involved rising from a deep squat with three different heel elevations: a full squat (FS), in which the plantar aspects of the feet were in full contact with the floor (0 degree), slope squat (SS), in which a 15-degree wedge was applied underneath the foot, and tiptoe squat (TS), in which subjects lifted their heels to their preferred height by extending the metatarsophalangeal joint. Electromyograms were taken of the extensor digitorum brevis (EDB), tibialis anterior (TA), rectus femoris (RF), and gastrocnemius (G) muscles. The results showed that heel elevation significantly affected the postural adjustment: TS caused significantly smaller anterior displacement in the knee and the hip during ankle dorsiflexion and minimized the duration of the forward movement required to stand. On the other hand, EDB activity strongly increased in TS. However, use of foot slope appeared to decrease activities of RF, TA, and EDB. These findings suggest that the use of a foot slope to achieve a squat-to-stand movement may be appropriate to assist patients with weak lower-extremity muscles.

The influences of monochromatic light were studied through measurement of EEG (Fz, Cz, Pz), ECG, blood pressure, pupil diameter, oral temperature, and subjective evaluation. The experiment employed ten young males (23±2.9yrs) with normal color perception. Three monochromatic light conditions were transmitted through three types of filter to produce three different wavelenghts (458 nm, 550 nm, 670 nm). The main effect of monochromatic light and the exposure time on EEG in Fz and Pz was significant. The alpha wave ratio was apparently lower in the 458-nm wavelength than in the other wavelengths (550 nm, 670 nm). The interaction between the light condition and the time was significant in pupil diameter. At 11 minutes of light exposure, pupil diameter in the 458-nm and the 550-nm wavelength light was obviously smaller than that in the 670-nm wavelength light. Moreover, at 19 minutes of exposure, pupil diameter in the 458-nm and the 550-nm wavelength light was significantly smaller than that in the 670-nm wavelength light. In conclusion, we estimated that arousal level increased during the exposure to 458-nm wavelength light. The effect of 458-nm wavelength light on the arousal level and pupillary reaction might be similar to the spectral sensitivity based on melatonin suppression described in recent studies. Therefore, this finding may support recent understanding of a non-visual system including the intrinsic photosensitive retinal ganglion cell (ipRGC).

Deep squatting places a burden on the lower limb muscles and influences postural balance. We attempted to determine the effects of postural changes on the rectus femoris, tibialis anterior, gastrocnemius, soleus, and extensor digitorum brevis muscles during squatting in 8 healthy male subjects. Three squatting conditions were involved: full squatting (FS), tiptoe squatting (TT), and tiptoe squatting on a 15°slope (TTS), performed randomly and recorded in a period of 4 min for each task. The influence of the squatting condition on electromyography and vertical ground reaction force parameters was examined in order to observe the effect of postural alteration on muscle activity and balance control. The results showed that the change of squatting posture from FS to TT decreased the activity of the rectus femoris and tibialis anterior muscles. FS has been suspected as a main cause of musculoskeletal complaint during prolonged squatting. In contrast, as the heel was lifted, the extensor digitorum brevis muscle increased to 39% of maximum activation. On the other hand, sway analysis at TT showed balance instability regarding the large area occupation of the center of pressure displacement. The presence of a 15°slope significantly reduced the muscular load. This simple study suggests that the inclusion of a sloping surface in daily activities that requires a squatting posture would be an effective means to reduce muscular load.

The purpose of this study was to investigate the influence of force tremor (FT) on the mechanomyogram (MMG) recorded by a condenser microphone (MIC) and an accelerometer (ACC) for the measurement of agonist and antagonist muscles during submaximal isometric contractions. Following determination of the isometric maximum voluntary contraction (MVC), 10 male subjects were asked to perform elbow flexion and extension at 20%, 40%, 60%, and 80% MVC. Surface electromyogram (EMG) and MMG of the biceps brachii (BB) and triceps brachii (TB) were recorded simultaneously using a MIC (MMG-_<MIC>) and an ACC (MMG-_<ACC>). We analyzed the root mean square (RMS) for all signals and compared the sum of the power spectrum amplitude (SPA) at 3-6 Hz and 8-12 Hz between the MMG-_<MIC> and the MMG-_<ACC>. During elbow flexion and extension, the RMS of the EMG and the MMG-_<MIC> of the agonist were significantly (p<0.05) higher than those of the antagonist in each contraction level. The RMS of the MMG-_<ACC> of the antagonist showed no significant (p>0.05) difference from that of the agonist, or tended to be higher than the agonist. The SPA of the MMG-_<MIC> of the agonist at 3-6 Hz and 8-12 Hz tended to be higher than the antagonist in elbow flexion and extension at each contraction level. The SPA of the MMG-_<ACC> of the agonist and that of the antagonist showed no significant (p>0.05) difference, or the antagonist MMG-_<ACC> tended to be higher than that of the agonist. These results suggest the MMG detected by a MIC appears to be less affected by FT than is the ACC because of its inherent characteristic to reduce FT in simultaneously evaluated agonist and antagonist muscles by means of MMG during submaximal isometric contraction.

Work requiring extremely body flexion is strongly associated with a high incidence of musculoskeletal injuries often reported during adopting squatting. In this study, the influence of different lower seat heights on the muscular stress in squatting on a stool (SS) were examined in comparison with fully squatting (FS). Fourteen healthy Indonesian males were recruited in the experiment. Two-dimensional body kinematics, ground reaction force (GRF) and electromyography (EMG) data were collected as subjects performed forward movement under four squatting height conditions which were FS and SS at 10 cm, 15 cm and 20 cm seat height. The results demonstrated that the change from FS to SS primarily affected the segmental angular flexions and muscular activities in the upper and lower limbs. GRF data showed that the SS conditions delivered 24% body weight onto the seat. The change of FS to SS showed significantly decrease in muscular load of the rectus femoris and tibialis anterior. In contrast, the soleus and gastrocnemius increased the activities as the seat height increased. The type of task that required the hand to handle the object on the ground level affected the trunk to be more flexed as the seat height increased. The findings of this study suggest that the use of a lower seat stool of a proper height seems to be a sub-optimal solution considering the change of muscular load associated with the discomfort in a squatting posture.

The present study investigated the circulatory responses to two mental tasks. Forty males and females performed a mental subtraction task and a color-word task. During each task, the systolic and diastolic blood pressure, mean arterial pressure, heart rate, stroke volume, cardiac output, and total peripheral resistance were measured as cardiovascular indices for a 5-min baseline, a 5-min task period, and a 10-min recovery period. As for the results, three hemodynamic reactivity patterns were verified: Pattern C, characterized by increased cardiac output and decreased total peripheral resistance; Pattern M, characterized by a moderate increase in both cardiac output and total peripheral resistance; and Pattern V, characterized by increased total peripheral resistance and decreased cardiac output. Also, four response types were found among all subjects: Type 1: cardiovascular responses showed the cardiac pattern for both tasks; Type 2: cardiovascular responses changed between the cardiac pattern and the mixed pattern with a change of tasks; Type 3: cardiovascular responses showed the mixed pattern for both tasks; Type 4: cardiovascular responses changed between the mixed pattern and the vascular pattern with a change of tasks. The comparison between types showed that Type 3 and Type 4 had an elevation in their blood pressure by an increased total peripheral resistance. On the other hand, Type 1 and Type 2 tended to have an increased blood pressure by a rise in their cardiac output. And Type 3 and Type 4 showed higher blood pressure and higher scores on the Type A behavior pattern questionnaire. In conclusion, at least four types of circulation response to the mental tasks existed, with Type 3 and Type 4 having higher blood pressure responses and tending to have an elevated blood pressure by a rise in their total peripheral resistance.

【目的】急速な高齢化に直面している我が国においては，重篤な合併症を引き起こす高齢者の転倒の予防・防止対策が急務となっている。高齢者の転倒予防には補償的バランス反応であるステッピング反応が重要と考えられる。本研究の目的は，後方向へのステッピング反応における，足圧中心の加速度とその制御に関わる筋力との関係について，若年者と比較した場合の高齢者の特性を明らかにすることである。<BR>【方法】対象は健常高齢者10名(平均年齢76.3±7.6歳)，対照群として健常学生14名(平均年齢21.9±2.6歳)を選定した。全ての被験者には口頭および紙面にて実験の趣旨を説明し，同意を得た後に計測を行った。被検者には左右分離式フォースプレート(Anima製G-6100)上で両足をそれぞれ別のプレートに位置させ，静止立位を20秒間保持させた。その後，検者の合図に従って，後方向へ重心を最大限移動し，片脚を後方へステップさせる課題動作をおこなった。課題動作中の足圧中心動揺をサンプリング周波数200Hzにて記録した。さらに被検者の筋力(腹筋群，腸腰筋，大殿筋，股内転筋群，大腿四頭筋，ハムストリングス，前脛骨筋，下腿三頭筋，長腓骨筋，後脛骨筋，足趾屈筋群)を携帯用徒手筋力計(HOGGAN HELTH INDUSTRY製 MICROFET)を用いて計測した。データ処理は，ステップ(フォースプレートから足が離れる)直前の足圧中心の側方向(L)と後方向(B)加速度値の合成成分(=√(L²+B²))を算出した。筋力は各被験者の体重で除した値(体重比筋力)を求めた。統計処理は合成加速度と筋力における若年群と高齢群の比較にWelchのt検定を用いた。さらに合成加速度と筋力との関係を知るために，合成加速度を目的変数，各筋力を説明変数として，棄却F値2.0でステップワイズ法による重回帰分析を行った。<BR>【結果】若年群と高齢群間で合成加速度値に有意な差は認めなかった。体重比筋力は全ての筋力において，若年群に比し高齢群が有意に低値を示した。合成加速度と筋力との関係は，重回帰分析の結果，合成加速度の有意な説明変数として，高齢群では長腓骨筋力と腸腰筋力が検出され(R=0.99，R²=0.98，p<0.01，r=-0.57)，若年群では中殿筋力が検出された(R=0.62，R²=0.38，p<0.05，r=-0.62)。<BR>【考察】本研究では，ステップ動作において力学的に不安定性が増加する足部の離床直前の足圧中心加速度を指標とした。重回帰分析の結果から，若年群の側後方向の加速度(不安定性)には骨盤帯の側方安定性の作用を有する中殿筋の筋力が関与していることが示唆された。高齢群では，足関節の外側安定性の作用を有する長腓骨筋の筋力および体幹部と大腿部を連結する腸腰筋の筋力の関与が示唆された。さらに，これら両群における違いは，後方へのステップ動作に用いる姿勢方略の違いが影響していると思われ，今後併せて調査していく必要性があろう。<BR>

The ultimate aim of this study is to develop a quantitative and objective method for designing toothbrush handles for ease-of-grip by means of ergonomic procedures. It is reasonable to think that easy-to-grip handles would enable more effective removal of dental plaque. To this end, the present study considered a hypothesis that the upper and lower part of the handle would have different roles, and have different optimum diameters depending on the human hand sizes when the handle is palm-gripped. To examine the hypothesis, 24 test toothbrushes were prepared combining a cylindrical upper part of 4 different diameters with a cylindrical lower part of 6 different diameters. Eighteen subjects were divided into 3 groups by their hand sizes. Electromyogram (EMG) of 5 muscles in forearms and hands of the subjects were measured when brushing. The handle diameter which gave minimum muscle load (MML) was calculated by the quadratic regression analyses of the EMG data. The analysis has demonstrated that the diameters with MML for each handle part have been obtained depending on the hand size. In conclusion, our hypothesis was appropriate and this study has shown that ergonomic procedures by EMG measurements are potential tools for designing toothbrushes for ease-of-grip.

本研究では身体に生じる加速度値から得られるゼロクロスポイント（ZCP）数を指標とし，高齢者の動的バランス評価における加速度計の有用性を検討した。対象はクロスオーバーステップ動作が可能な健常高齢者9名と健常若年者11名とした。分離型Force plateの床反力値から，ステップ動作における静止立位期と片脚立位期を区分し，各期の動揺量とZCP数について高齢群と若年群で比較した。結果，片脚立位期のZCPでは若年群に比較し高齢群で有意に低値を示した（p＜0.01）。結論として，本研究で用いたZCP数を指標とすることで，動的バランスにおける高齢者の姿勢調節の特性をより詳細に評価できる可能性が示唆された。<br>

Indonesians commonly perform activities on the floor that require squatting postures. It has been identified that adopting squatting postures without any proper support would gradually cause postural stress. This study examines the influence of different squatting heights to the body kinematics and subjective discomfort rating. The subjects were divided into two different body types: overweight subjects with BMI>24.9 and normal weight subjects with BMI 18-24.9. The subjects adopted a squatting posture at no-stool condition and at the stool height of 10, 15, and 20 cm. The task was to simulate the work close to the ground level with the hip joint deeply flexed. Body segmental angular flexion (SAF) and the visual analog scale (VAS) method were selected for parameter analyses. Significant differences were found in both parameters SAF (trunk, hip, knee, and ankle) and VAS. The interaction effect was found by squatting height and the body type for SAF of the trunk (p<0.05). However, the increasing BMI index was also found significantly affected associated with the anthropometrical characteristics for buttock height and lower limbs depth. It is suggested that normal weight subjects sit comfortably at 15 cm stool height, whereas overweight subjects preferred 20 cm stool height as a better acceptability condition in terms of overall parameter analyses.