Intracellular biochemical changes could be monitored noninvasivery and continuously by using nuclear magnetic resonance (NMR). In about the last decade, intracellular behavior of phosphorus compounds and pH during muscle contraction in man have been studied by 31P nuclear magnetic resonance spectroscopy (31P-MRS). During incremental load, lactic acidosis was followed by a decline in intracellular pH. 31P-MRS studies has been definitely proved that this change in intracellular pH shows the threshold behavior. Some reports discussed the intracellular pH threshold (pHT) as an anaerobic threshold (AT) from the view point of intracellular events. However, our studies revealed that pHT did not reflect the onset of lactate production. In this article, studies of intracellular pH of working muscle were reviewed in relation to an anaerobic threshold.
Seven healthy young male students participated in this study. Each subject sat on a chair in an anteroom at 25°C for 30 min and then entered a climatic chamber, controlled at 40°C and R.H. 50% and sat on a chair for 90 min. Cooling of frontal portion including the region around the eyes (FC), occipital portion (OC), and temporal portion (TC) began after 50 min of entering. An experiment without head cooling (NC) was also made for the control measurement. Thermal comfort and thermal sensation were improved by head cooling, but response was the same regardless of portion cooled. Although rectal temperature, mean skin temperature and heart rate showed no significant effect due to head cooling, forearm skin blood flow (FBF), sweat rate (SR), and body weight loss (ΔWt) had a tendency to be depressed. FBF in FC and TC decreased during head cooling, but that in OC and NC did not change significantly, while SR in FC was depressed. ΔWt showed total sweating to decrease by FC and TC, and FC to have greater inhibitory effect on sweating than OC. Thermal strain was evaluated by the modified Craig Index (Is). Is in FC decreased significantly more than in NC. Cooling of other portions of the head had no significant effect on Is. Cooling of the frontal portion of the head may thus be concluded to have the most effect on thermoregulatory response in a hot environment.
This paper reports on the investigation of palm sweating during short-term memory tasks and testing the availability of the amount of palm sweating for an index evaluating mental strain. Six male subjects performed sets of thirty tasks with digit strings ranging from 4 to 9 digits at random order. The correctness of recalled answer, subjective difficulty for mental stress and palm sweating at each task were recorded. The amount of palm sweating (PS) was measured using hygrometry with a ventilated capsule attached on the left palm. Correct answer rates suddenly decreased over 7 digits. Subjective difficulty tended to increase with an increase in string-length. PS tended to decrease exponentially with the repetition of tasks at each string-length, and the exponential regression curve was fitted between PS and order in tasks at each string-length. Estimated PSs were obtained at 1st, 15th and 30th tasks from the regression curves. Estimated PS at 1st task tended to increase in proportion to string-length. Each estimated PS at both 15th and 30th tasks had a threshold for increasing. Also, estimated PS increased in proportion to the string-length at no less than the threshold. The thresholds were 5 digits at 15th and 6 digits at 30th task. These present findings suggest that PS is an index available for measuring mental strain. Also, this index describes the level quantitatively in adaptation for mental stress.
The purpose of the present study is to evaluate the static work load as a model work in Submersible Decompression Chamber (SDC) during a deep sea saturation dive with helium-oxygen gas mixture. Heart rate (HR) and electromyogram (EMG) power spectrum changes were studied during a 7-minute static work, half-rising posture or flexed knee posture in four healthy male subjects. During the static work, EMG of the rectus femoris was recorded with surface electrodes, and changes in the EMG power spectrum were presented in the ratio of a high-frequency to low-frequency band (H/L ratio) after the Fourier transform analysis. The HR decreased at 31 ATA and increased remarkably after the decompression to 1 ATA. HR at post-decompression was higher than pre-compression. The lowering phenomena of EMG presented by H/L ratios during the static work were similarly observed in all three conditions. But the changes of the high and low frequency components were different in the post-decompression condition from the pre-compression and 31 ATA conditions. HR as a parameter of static work load might underestimate the work load at the hyperbaric environment due to hyperbaric bradycardia and overestimate it after decompression by “decompression tachycardia.” The EMG lowering phenomenon observed after decompression might not be caused by the same mechanism as seen in the pre-compression and hyperbaric environments. Extreme care must be taken to evaluate the static work load not only at hyperbaric helium-oxygen environments but after decompression from a deep saturation dive.
Heart rate variations during steady state respiration with various frequencies were studied on seven healthy male students at two different body positions. Respiration was controlled at four different frequencies (0.083, 0.100, 0.200, 0.250Hz), and the tidal volume was simultaneously controlled at 1500ml (0.083, 0.100Hz) or 1000ml (0.200, 0.250Hz:). A tilting bed was used for changing body position, and the measurements were conducted at horizontal and vertical position. RSA (respiratory sinus arrhythmia) amplitude at 0.250Hz was significantly decreased at vertical position compared with horizontal position. At 0.200Hz the significant decrease could not be obtained although some tendency of decrease appeared. Contrary to these high frequencies, the amplitudes at low frequencies (0.083, 0.100Hz) were significantly increased (p<0.01) during vertical position. This postural effect on the low frequency RSA could be regarded as a similar result on MWSA (Mayer wave relate sinus arrhythmia) which reflects sympathetic nervous activity. Furthermore, the ratio between the amplitude at 0.100Hz and that at 0.250Hz was significantly correlated with mean heart rate (n=56, r=0.73). From these results it was assumed that the RSA amplitude at low frequency associate a with not only parasympathetic nerves but also sympathetic nerves whereas the amplitude at high frequency was solely mediated by parasympathetic nerves.