The constrained posture used for work using a visual display terminal (VDT), such as data entry, can produce static muscular fatigue. Based on the application of ergonomic principles, we conducted an experiment using a prototype VDT chair designed with an armrest adjustable to heights from 22 to 28 cm. The experiment-conducted to assess the static muscular strain based on varying heights of the armrest and distance from the keyboard-was performed with male subjects. The subjects were asked to input five-figure numbers using the 10 keys arranged on the right side. Using a surface electromyogram, we measured the strain imposed on the arm and the shoulder. This was followed up with a performance, weight-loading onto the armrests and a questionnaire. Results show that use of armrests is effective for the alleviation of muscles in one-handed keyboard operation where operators work on a desk whose height is unadjustable according to their body height or where operators are unable to rest their wrist on the desk. A chair with height-adjustable armrests is considered desirable when used by several people.
Ventilatory response to eucapnic sustained mild hypoxia was measured in one patient with unilateral and three patients with bilateral carotid body (CB) resection (defined UR and BR, respectively). The profile of ventilatory response in UR patient was initially augmented then gradually declined (biphasic pattern) as generally seen in normal subjects although the absolute magnitude was substantially low. On the other hand, biphasic pattern was disappeared in all three BRs. Lack of hypoxic ventilatory decline (HVD) in the late period of sustained hypoxia was in marked contrast to that reported in the anaesthetized and CB-denervated animals whose ventilation was severely depressed lower than the pre-hypoxic control level. In view of recent knowledge that the analogous mild hypoxia in normal animals and humans elicits an useful adaptation to economize energy expenditure with maintaining reversible excitability in control of respiration, BR patients were considered to have lost this ability. We conclude that in awake humans the CB not only stimulates ventilation but also controls the degree of subsequent HVD during sustained hypoxia.
The aim of the study, was to estimate the reaction of selected circulatory system parameters to psychic workload in industrial managers and to answer the question whether may affect this reaction. The study was performed in 23 men (mean 46 ± 6 years of age) and 16 women (mean 42 ± 6 years of age), employed as executives in a large industrial plant. The subjects had their 24-h ECG recorded using Medilog 3000 (Oxford). The ECG recordings were classified as pathological according to the standards of Bjerregaard. Heart rate was calculated for working time, leisure time and sleep. The subjects were also asked to estimate the perceived psychic load according to a method involving subjective estimation of work-demands and of an ability to cope with them. Generally, the subjects reported high work demands, but coping abilities were higher than work demands. Both in the men and women, a relationship was found between the intensity of subjective estimation of psychic load and heart rate response. However, the reaction of the circulatory system to the psychic workload in men was long-lasting (its effects continued until late at night); in women it was more direct (only during work). The frequency of abnormalities in 24-h Holter ECG recordings for both test groups was not very high, a little higher in men (30%) than in women (25%), and was comparable with the frequencies in selected general population groups. Our results may indicate that mental workload of the managerial staff, does not cause increased frequency of ECG abnormalities. However, in view of the fact that cardiovascular diseases are more frequent among men than among women, different reaction of the circulatory system to workload should also be accounted for in an attempt to explain the sources of that phenomenon.
This study was designed to test whether high-salt diet intake has some acute impaired effect to the muscular exercise ability due to the calcium deficit in muscle cell via the accelerated sodium-calcium exchanger. Six healthy young Japanese women (aged: 22.3 ± 1.9 yr) performed two types of muscle strength tests and ramp mode cycle ergometer exercise until exhaustion after normal- (NaCl is approximately 5.6 g) and high-salt (21.0 g) controlled diet intake on two separate days in random order. The urinary sodium excretion sampled during 12 hours on the high-salt diet day was significantly higher compared to that of normal-salt diet day (3301 ± 992 vs 1595 ± 540 mg; P<0.05), while there was no substantial difference between the urinary calcium excretion in high- and normal-salt diet days (58.6 ± 19.7 vs 55.0 ± 17.2 mg; ns). There were no significant differences in back strength, repeated maximal hand grip exercise ability, and VO2max and duration time during ramp exercise between high- and normal-salt diet conditions. It was concluded that high-salt diet intake even exceeding 20 g per day had substantially no acute effect on muscular exercise ability in young Japanese women.
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