In this short review, the frame of current understandings concerning what determines the upper limit of oxygen flow from the ambient air to the muscu-lar mitochondria during maximal dynamic exercise in humans (i.e., VO2max), was summarized mainly from its modeling perspective. Several models and experirnental evidences which appeared repeatedly in the recent debates regarding the factors limiting V02max, were adopted and criticized. In conclusion, V02max is determined in particular by the integrated interaction between the diffusive and convective factors both to lung 02-loading and muscular 02-unloading in the path-way for 02 flow, although all experimental observations cannot be satisfactorily explained at the present time.
Liquid cooled garments (LCG) are a powerful tool for alleviating heat strain during work in hot conditions. However, the potential advantage of an LCG depends on a more or less proper control of the cooling liquid's temperature. To gain more knowledge on this subject two experimental studies concerning manual control by the wearer were carried out. In both studies the subjects had to exercise in a warm environment. In the first study the subjects (n = 5) were asked to control the temperature directly. They used different strategies, ranging from gradual changes to oscillations of the suit temperature. This was accompanied by large differences of the chosen inlet temperature and the comfort level attained, although by repetition of the experiment it was possible to increase the subjective thermal comfort. In the second study a technical 'comfort' controller changed the inlet temperature of the LCG in the appropriate direction whenever the personal assessment of thermal sensation differed from the neutral state. The subjects (n=6) had no information about the control mode. The experiments showed that it was possible to maintain a comfortably neutral thermal sensation throughout nearly the whole experiment. This result, however, was partly in contrast to the objective thermal state of the subjects. Two of them had problems with their heat balance, expressed by the fact that their rectal temperature did not reach a steady state. The results of both studies indicate that manual or subjective control is not optimal and should therefore be replaced by an objective control of the thermal state.
Six male and six female students (19-23 yrs) volunteered as subjects in the present experiment. Subjects performed the data entry tasks. A hundred and twenty single digit numbers 12 by 10 Iines matrix were displayed in a random sequence on the left side of monitor. Subjects input the same numeral as these numbers one by one with clicking of the mouse on the ten keys displayed on the right side of the monitor. Each task consists of the following conditions: 1) system response time is fast or slow; 2) delete the input numerals from 120 numbers or not ; 3) button flashes after input or not; and 4) the remaining time is displayed or not during performing the tasks. These tasks are programmed to be finished automatically after 200 seconds independent of the rate of completing all inputs. We measured heart rate (HR), systolic and diastolic blood pressure (SBP and DBP), skin blood flow (SBF), skin potential level (SPL), number of errors (Es), total number of input and subjective ratings concerning the degree of irritation (SR1), difficulty of input (SR2) and unpleasantness in operation (SR3). It was shown that when system response time was slow, even the average of heart rate and blood pressure were lower than fast system response time, however, the subjects felt greater emotional irritation, difficulty of input and unpleasantness in operation hence making more errors.
Small computers are much in demand for mobile computing. However, keyboard size is an obstacle to further size reduction. Reducing the space occupied by keys would affect the usability of the keyboard. On the other hand, if the keys were closer together, the fingers would reach them faster. This could improve typing performance. An experiment was therefore conducted to investigate the relationship between users' performance and the center-to-center key space of reduced-size keyboards. Eighteen touch-typists were asked to do a word typing task on five different keyboards. A standard keyboard with a key space of 19.05 mm and smaller keyboards with key spaces of 16.7, 16.0, 15.6, and 15.0 mm were used in this study. No performance degradation was found on keyboards with a key space of 16.7 mm for faster typists (those capable of about 40 wpm), including those with large fingers (97.5 percentile of Japanese adult males). For faster typists with narrow fingers, there was no performance degradation on keyboards with a key space of 15.0 mm.
Mean arterial blood pressure (MAP) is a common characteristic of the cardiac cycle. Usually it is evaluated by assuming that the left ventricular ejection time (systole) constitutes a constant proportion of the cardiac cycle (i.e. 1/3), regardless of the heart rate (HR). However, elevation of HR during exercise results in a reduction of the duration of the ejection period and even a greater reduction of the ventricular filling period. Therefore, a constant diastole/systole proportion at various heart rates may be misleading. The purpose of this study was therefore to evaluate the accurate proportion of the systolic period from the cardiac cycle at different metabolic rates and calculate MAP accordingly. Twenty healthy subjects (age: 20-50 yr.) exercised at different work intensities on a cycle ergometer to elicit HR in the range of 55-180 bpm. During the ride the mitral and aortic flow velocity wave form were recorded by Doppler echocardiography; the mitral flow from the apical view and the aortic flow from the apical long axis view. Blood pressure was measured using a sphygmomanometer. The fraction of systole (St) from the heart cycle was related to HR and was described in mathematical terms as: St= 0.0lexp(4.14-40.74/HR) MAP was then calculated from the diastolic blood pressure (dBP) and the pulse pressure (PP) adjusted for St as follows: MAP-dBP+St· PP;(mmHg) The use of the suggested model reduces errors in the evaluation of various cardiac parameters which are related to arterial pressure, such as peripheral resistance, especially under exercise-heat stress.
In this study, for determining the influence of different life style on the serum (αhydroxybutyrate dehydrogenase activity (αHBD), we carried out surveys and laboratory studies on the relationships of the nutritional intake, physical activity, cigarette smoking and alcohol consumption of young females with their serum αHBD activity. There are significant positive correlation between αHBD and GOT, GPT, LDH, CPK, phospholipids, total cholesterol, and HDL-cholesterol, and significant negative correlation between αHBD/LDH and GOT, GPT, and γGTP. There are significant positive or negative correlation between αHBD and systolic pressure, diastolic pressure, cardiac index, stoke volume and total periperal resistance, and significant negative correlation between αHBD/LDH and vital capacity in young females. The serum αHBD activity levels of nonsmokers was siginificant higher than those of smokers(p 0.05). There are significant positive correlations between serum αHBD activity and beverage con-sumption, and between αHBD/LDH and protein, calcium, vitamin A, B1, B2, C, pulses, vegetables and milk in young females. The finding shows that the group of serum αHBD activity level of 240 or more units exhibited higher level of rate of those who exercised sometimes + usually than the other group in young females. However, the serum αHBD activity level did not show siginificant correlation with energy expenditurs per day. Exercise at 50 and 70% V02max may produce a significant increase in their serum αHBD activity. There is a possibility that serum αHBD activity may serve as an indicator for ones health condition. It is undeniable that observation of variation of serum αHBD activity is highly significant in health maintenance.
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