Eight Japanese men and women participated in this study. They were randomly exposed to two environments: hot-dry; HD (Ta=40°C, rh 30%, wet bulb globe temperature (WBGT)=32°C) and hot-wet; HW (Ta=31°C, rh=80%, WBGT=32°C) for 110 min. During the exposure, they rested on a bicycle ergometer for 20 min during rest and 30 min during recovery, then they pedaled it with an intensity of 40% Vo2 max for 60 min. Tre, Tsk, and HR were recorded every minute. Total sweat loss and dripping were measured by independent bed balances which was connected to a computer processing with an accuracy of 1 g throughout the experiment. Sweat sodium concentration at forearm and back sites were collected by sweat capsule technique. These results showed that ΔTre, Tsk, evaporated sweat, dripping sweat, body heat storage of both sexes in HD were significantly higher than these in HW during exercise. HR of men in HD at the end of recovery was slightly higher than that of women. Whereas the sweat sodium concentration at forearm and back sites in both sexes remained unchanged either in HD or HW environment, it was found that HD was more stressful than HW environment under equivalent WBGT.
The peripheral chemoreceptors play a dominant role in the respiratory compensation of lactic acidosis during heavy exercise of humans. Our object was to determine the contribution of peripheral chemoreceptors to exercise hyperpnea during mild to moderate and heavy exercise above the anaerobic threshold. We used a hyperoxic suppression test in six normal male subjects. Inspired gas was abruptly changed without the subject's knowledge from air to pure oxygen for 5 to 6 breaths. The maximal ventilatory depression after O2 breathing was 5.5 ± 1.7 L/min (BTPS) at mild exercise, and the depression increased with increasing exercise intensity up to 12.8 ± 4.1 L/min (BTPS). The relative contribution of the peripheral chemoreceptors to ventilation in terms of percentage of the maximal ventilatory depression was maintained, being 20% throughout the entire work ranges studied. The contribution of the peripheral chemoreceptors to total ventilation is hardly altered by lactic acidosis caused by heavy exercise above the anaerobic threshold according to our data. These results suggested that the peripheral chemoreceptors may not be solely responsible for excessive hyperventilation, or residual activities of peripheral chemoreceptors still exist after O2 breathing especially during heavy exercise above the anaerobic threshold.
The fastest growing age group in the United States and Japan is the elderly. There is a need to develop appropriate exercise training guidelines designed specifically for healthy older persons. Recent reports have shown that the lactate threshold (LT) can be used to evaluate the clinical significance of aerobic power (VO2max) and its effect of exercise training in the elderly. However, there is a lack of research comparing the LT between well-trained and sedentary elderly individuals. Also, the effect of exercise training on the heart rate (HR) at LT needs further investigation. The purpose of this study was to compare the LT levels between the older trained men (T group; n=72, age=71.3 ± 5.8 yr, range 60-85 yr) and apparently healthy but untrained elderly men (U group; n=172, age=72.2 ± 5.7 yr, range 60-93 yr). The LT was measured during an incremental cycle ergometer test. A low relationship was found between VO2 corresponding to LT (VO2LT) and age in the T (r=0.20, P<0.05) and U groups (r=0.43, P<0.05). A significant difference was found in the VO2LT between the T and U groups. The absolute VO2LT corresponded to approximately 6 and 4 METs for the T and U subjects, respectively. However, there was no significant difference in HR corresponding to LT (HRLT) between the two groups (T; 109 ± 19 b·min-1, U; 107 ± 13 b·min-1). The data show that the absolute VO2LT is higher for T than U elderly subjects and is associated with a HR of approximately 108 b·min-1 for both groups. Recommended exercise intensity in terms of HR may not differ between trained and untrained elderly men.
The purpose of this study was to investigate the effects of wearing two different clothing ensembles on endurance performance of handgrip exercise in eight female subjects in the climatic chamber (25 ± 1°C, 50 ± 10%RH). The experimental clothing ensembles were HALF and LONG. The clothing ensemble HALF consisted of half-sleeved shirts, knee-length trousers and sandals; LONG of long-sleeved shirts, long trousers, socks and walking shoes. The subjects carried out the preliminary exercise for 1 hr as scheduled which was composed of slow running on the horizontal treadmill for 25 min, rest for 10 min and running again for 25 min the same as the first running. After the preliminary exercise, the subject exercised with a hand ergometer lifting a weight of 15% of maximal voluntary contraction at the rate of 35 contractions per min until volitional exhaustion. Rectal. temperature, skin temperatures, heart rate, body weight loss, clothing microclimate, number of contractions were measured during the experiment and compared between two clothing ensembles. An important result was that the endurance performance of handgrip exercise was significantly greater in HALF than in LONG, for which the lower maintenance of core temperature and mean skin temperature in HALF during the l hr preliminary exercise might be responsible. Our present and former results indicate a significant participation of clothing for the endurance performance of handgrip exercise.
Folk wisdom suggests that chicken extract is useful for recovery from physical and mental fatigue. To explore this question, the physiological effect of Brand's Essence of Chicken (BEC), a popular chicken extract used as a traditional remedy, was assessed during recovering from mental stress. We quantitated the blood levels of stress-related substances, and examined the task performance and subjects' mood states during mental workloads. Subjects were 20, healthy male students who have never tasted BEC. They took two bottles of BEC or a placebo (70 ml/bottle) daily in the morning for 7 days. On the final experimental day, two mental workload tests were performed: (A) a mental arithmetic test (MAT; 1600 trials of two or three figure-addition or subtraction for 40 min). (B) a short-term memory test (SMT; 20 trials of memorizing 9 digit numbers). Blood was collected before and after each workload task. After the mental workload, the recovery of mean cortisol level of subjects who consumed BEC was significantly faster than that for those consuming the placebo. The task performance of subjects performing the MAT and SMT was also improved with BEC consumption compared with placebo. According to the profile of mood state questionnaire, subjects felt more active and less fatigued during the workload when they took BEC regularly. We conclude that the extract of chicken has the potential to metabolize stress-related substance in blood and to promote recovery from mental fatigue.
We tried to discriminate different forearm's motions by surface EMG signals using neural network. In order to get a higher discrimination rate, the positions of electrodes were improved. We also tried to discriminate similar motions in order to clarify the limitation of the discrimination by surface EMG signals. Two experiments were carried out. One was to discriminate five different motions: grasp, wrist flexion, wrist extension, forearm pronation, and forearm supination (Experiment 1). The other was to discriminate four similar motions which have different quantitative definitions at grasp, wrist flexion/extension, or forearm pronatio/supination (Experiment 2). Four surface electrodes were placed on the skin above the main active muscles: short radial extensor m. of wrist, supinator m., long radial extensor m. of wrist, and ulnar flexor m. of wrist, considering anatomical functions of the forearm's muscles. EMG signals were recorded during 2 sec while the subjects kept the motions. Recorded EMG signals were sampled at 200 msec intervals after full-wave rectifying and low-pass filtering. Therefore, the number of sampling data patterns of EMG signals was 10 for every motion. Three layers of neural network was used for discrimination. The number of units in the input layer is 4, and the number of units in the output layer is 5 or 4. In order to get the best discrimination rate of the motions, we changed the number of units in the hidden layer from 3 to 12. The neural network was trained by the back-propagation algorithm. In Experiment 1, the best average values of discrimination rates under three pattems of EMG signals for each subject were 96.0%, 98.0%, and 87.2% when the numbers of units in the hidden layer were 10, 11, and 3 respectively. In Experiment 2 using original EMG patterns, the best average values of discrimination rates at grasp, extension/flexion, and pronation/supination were 59.5%, 76.0%, and 25.0% respectively. By using normalized EMG patterns, these were 40.0%, 84.8%, and 55.5% respectively.