RESUMEN
Physiological responses to heat and heat tolerance were examined in summer and winter on 13 male athletic university students and male nonathletec university students. After staying for 30 min. in a climatic chamber maintained at 30°C with 70% relative humidity, sweating reaction was examined far 90 min, by immersing both legs up to the knees in a stirring water bath of 42°C.<BR>Both groups showed significantly greater sweat volume, significantly lower Na concentration in sweat and considerably lower rise in rectal temperature and less increase in heart rate in summer than in winter. In both seasons, athletes showed smaller volume of sweat, lower Na concentration in sweat, lower rise in rectal temperature and less increase in heart rate than nonathletes.<BR>It is concluded that heat tolerance of athletes was superior to that of nonathletes when assessed by our heat tolerance indices and this superior heat tolerance of athletes could be explained due to a result of physical training. Heat tolerance index, representing the magnitude of physiological strain in the body induced by heat load, was modified by using relative increase in heart rate in place of salt loss. It can be said that the modified heat tolerance index is useful as a substitute of the original heat tolerance index in field studies.
RESUMEN
It had been proposed by Kurata that relative threshold value F<SUB>th</SUB> of single motor units depends on the gradient G (kg/sec) of the tension increase of muscle in such a manner as<BR>F<SUB>th</SUB> (≡T.G) =ρG<SUP>λ</SUP><BR>Here T<SUB>1</SUB> is the time interval from the onset of EMG to the moment of recruitment of a motor unit and ρ is a proportional constant. The motor unit with a <I>positive/negative</I> value of λ is characterized to be <I>static/phasic</I>.<BR>Morimoto and Hasegawa reported that the above relation also holds for the relaxation period, provided that Ftn and G are replaced by the tension at the moment of silence and the absolute value of G, respectively. In this case, the motor unit with a <I>positive/ negative</I> value of λ is characterized to be <I>phasic/static</I>.<BR>In order to investigate the characteristics of motor units during relaxation period under the influence of pre-relaxation states, such as the increase of tension up to 4kg at the gradient of 0.5kg/sec and the state sustained at 4.0kg for 30sec. Single motor units of <I>m, vastus medialis</I> were studied by the same method as that of Morimoto and Hasegawa.<BR>The following results were obtained;<BR>1) Both at contraction and relaxation periods, the above relation was confirmed.<BR>2) The motor unit with characteristics of recruitment modes was influenced by the pre-relaxation state, but its tendency was not definite. These results suggest that <I>phasic/static</I> characteristics of motor units are not stationary but fluctuate depending on the pre-relaxation states.
RESUMEN
In this study, the relationships between the contractile properties of human motor units and their discharge patterns, characteristics of recruitment and others were examined. Action potentials of single human motor units in<I> m, extensor digiterum</I>were detected by use of an inserted electrode. Tension curves of single motor units were recorded under the conditions that tension in finger extension was gradually increased, and that the subject relaxed his muscle as soon as he observed a sweep on a Braun tube triggered by the action potential of a single motor unit. About 100 twitch tension curves were summed up to obtain the average tension curve of a single motor unit. The τ-S diagrams were obtained from the mean discharge intervals (τ) of motor units at various sustained tensions and their standard deviations (S) . The λ values were also obtained from the relation F<SUB>th</SUB> (-T<SUB>1</SUB>G) =ρG<SUP>λ</SUP>.<BR>It was observed that the contraction time of the twitch tension curve of single human motor unit in a muscle was nearly proportional to τs (the τ values at a constant S value) . We presume that the regularity of discharging of motor unit affects the contraction speed in human muscle, because the motor unit with more regular discharging has longer contraction time of twitch.
RESUMEN
In order to examine some aspects of the function of the sensory-motor cortex in voluntary movements, the selective reaction was studied against photic stimulation.<BR>An experimental board was constracted, on which there were 12 lamps equally spaced on a circle (radius 32cm) and a key at the center of the circle.<BR>An electrical signal appeared when a lightening lamp or the lamp at the opposite position relative to the lightening one touched. Ten healthy male and female subjects were selected, whose age ranged from 19 to 32. The subject stood in front of the board, softly touched the key with his/her Digitus Medius and looked at the key. The surrounding lamps were imaged on the field of indirect vision. When one of the lamps was lightened, the subject touched as quickly as possible the lightening lamp (named this action as “catching action”) or the opposite lamp (“avoiding action”), following the initial instruction. The following three cases were studied : (a) 2 directions ; one of the two lamps (NO. 1 & 7) was lightened, (b) 4 directions ; one of the four lamps (No. 1, 4, 7 & 10) was lightened and (c) 12 directions ; one of 12 lamps was lightened. This order was assumed to be in the increasing load condition. The EMG was also recorded, so that we could measure the following five characteristic time<BR>1. Total Time (TT), the time interval between the moment of lightening of a lamp (light stimulation) and the moment of touching the target lamp.<BR>2. Reaction Time (RT), the time interval from the beginning if the light stimlation to the release of the finger from the key.<BR>3. Muscle Contraction Time (MCT), the time interval from the release of the finger from the key to the moment of touching the target lamp.<BR>4. Premotor Time (PMT), the time interval from the beginning of the light stimulation to the onset of discharge on EMG.<BR>5. Motor Time (MT), the time interval from the onset of discharge on EMG to the release of the finger from the key.<BR>The following results were obtained ;<BR>1) In both cases of the dominant and non-dominant hands, TT, RT and MCT were longer in the avoiding than in the catching actions. This trend was independent of the above three load conditions.<BR>2) In both catching and avoiding actions, most of the experimental results distributed nearly normally on the histograms of frequency versus characteristic time<BR>3) When the load condition was changed from (a) to (c), RT and PMT clearly shortened but no appreciable change in MCT was observed in the catching action, while RT showed a trend to lengthen in the avoiding action.
RESUMEN
It had been proposed by Kurata that the relative threshold value F<SUB>th</SUB> of single motor units depends on gradient G (kg/sec) in the tension increase of muscle in such a manner as<BR>F<SUB>th</SUB> (=T<SUB>1</SUB>⋅G) =ρ⋅ G<SUP>λ</SUP><BR>Here T<SUB>1</SUB> is the time interval from the onset of E.M.G. to the moment of recruitment of a motor unit and ρ is the proportional constant. The motor unit with a positive/negative value of λ is characterized to be static/phasic.<BR>In order to confirm the above relation and to see whether or not the relation is also valid in the relaxation period, single motor units of<I> M. VAST US MEDIALIS</I> were studied by the same method as that of Kurata.<BR>The present findings are<BR>1) At the contraction period the aove relation was confirmed.<BR>2) At the relaxation period the above relation also holds, provided that Ftn and G are replaced by the tension at the moment of silence and the absolute value of G, respectively. The motor unit with a positive/negative value of λ is characterized to be phasic/static.<BR>3) The value of Ftn and λ at the relaxation period are not the same as those at the contraction period.