Effects of local cooling and heating in the triceps surae muscles during sustained isometric contraction / 体力科学

A study was conducted to examine activity patterns of surface electromyograms (EMGs) in the triceps surae muscles (medial gastrocnemius, MG ; lateral gastrocnemius, LG ; soleus, SOL) during isometric contraction in plantar flexion (60% MVC, 20% MVC) after immersion in water at three different temperatures. Seven healthy male subjects were immersed in water at 2-3°C (ICE), 19-21°C (MID), and 40-42°C (HOT) . The results of the study are summarized as follows :<BR>1) In the MG and LG, there was a slight increase in the rate of integrated electromyograms (IEMGs) in the MG (the main agonist muscle) . However, the rate of increase in the LG, which is the synergistic muscle, was much greater than that in the MG when contraction was sustained at 60% MVC. Therefore, the activity pattern suggests that muscle activity in the LG compensates for that in the MG.<BR>2) The IEMGs of the SQL with sustained contraction, increased significantly after immersion in HOT and MID, but the IEMGs decreased after immersion in ICE. These results suggest that the recruitment threshold in slow-type motor units should increase during sustained isometric contrac-tion in ICE.<BR>As illustrated above, the activity of the LG increased to compensate for that of MG. In the SQL, muscle activity with sustained contraction decreased in ICE. These results suggest that control mechanisms of the central nervous system might play an important role in the associated movement of the triceps surae muscles.

Time course of twitch potentiation after tetanic nerve and direct stimulations in the thumb adduction in man / 体力科学

Effects of various tetanic stimulation frequencies (50 Hz, 100 Hz and 200 Hz) on the time course of twitch potentiation were examined in the adduction of human pollicis. Isometric twitch tension curve and surface electromyogram were recorded immediately after (1 sec) the 10 sec-tetanus and at intervals of lOsec (up to 300sec) . The stimulating methods were by nerve and direct stimulations in order to examine the role of nerve on the post-tetanic potentiation. The results were summarized as follows :<BR>1) The greatest potentiation was observed immediately after the tetanus. The potentiation decreased rapidly in the period of 60 sec after the tetanus. Then, the potentiation continued to decrease at the low frequency (50 Hz) ; however, it tended to level off at the high frequencies (100 Hz and 200 Hz) .<BR>2) The time course of twitch potentiation by the nerve stimulation was larger than that by the direct stimulation. This result suggests that nerve has a factor which enhances potentiation. The duration of the potentiation varied according to the stimulation frequencies by the nerve stimulation. It seems that this phenomenon was strongly influenced by the nerve.<BR>3) The degree of increase in twitch tension tended to depend greatly on the peak rate of force development. This result suggests that the increase in twitch tension was closely related to the intensity of the active state.<BR>4) Time course of time to peak tension relatively corresponded to the half relaxation time. It seems possible for the duration of the active state to be related to calcium uptake at the sarcoplasmic reticulum.<BR>5) The coupling efficiency by the direct stimulation tended to be smaller than that by the nerve stimulation after 10 sec. This result suggests that the stimulating nerve possesses a factor which prolongs the period of potentiation.

Changes in activity in triceps surae muscles during prolonged isometric contractions / 体力科学

In order to examine muscle activities, surface electromyo-grams (EMGs) were recorded from the triceps surae muscles (lateral gastrocnemius: LG, medial gastrocnemius: MG, soleus: SOL) during prolonged isometric contractions at 20°of ankle joint angle under constant load (10% MVC) . The results were summarized as follows;<BR>1) EMG recordings were obtained which showed complementary activity in each muscle in the time course. Changes in activity was found between whole muscles in the synergist of triceps surae muscles.<BR>2) Muscle activity most frequently took the form of MG+SOL, followed by MG acting alone and SOL acting alone. Ta/Ts value (the ratio of total activity period and total silent period on EMG activity) showed 4.0 in MG and SOL. In contrast, it showed 0.3 in the LG.<BR>3) In the latter half of all exercise times, frequent changes in activity were shown, and Ta/Ts value increased in the gastrocnemius muscle and decreased in the soleus muscle. These results indicate that frequent changes in activity in the latter half were caused by the reduc tion in Ts in the gastrocnemius muscle, and the reduction in Ta in the soleus muscle.<BR>4) Mean integrated EMGs increased significantly in the middle and latter phases in each burst activity, but those in the latter phase did not increase compared to those in the middle phase. These results suggest that the rotation of activity between muscles may have occured before the remarkable increase of EMG activity with fatigue.

Electromyogram patterns during ankle joint movements at various angular velocities in the triceps surae muscles / 体力科学

Surface electromyograms (EMGs) were recorded from the triceps surae muscles in order to examine muscle activities during concentric and eccentric ankle joint movements at various angular velocities under constant load (5 and 10%MVC) . The results were summarized as follows ;<BR>1) At slow angular velocity (6 deg/s) of ankle joint movement, EMG amplitude tended to increase at a larger ankle joint angle in the gastrocnemius muscle, and at a smaller angle in the soleus muscle.<BR>2) Following an increase in angular velocities (6→30→60 deg/s), peak values of integrated EMGs were significantly increased (7-15%) in the medial gastrocnemius muscle. However, these peak values were significantly decreased in the soleus muscle (22-49%) . These results suggest selective recruitment of motor units depending on angular velocity.<BR>3) Ankle joint angle at the peak integrated EMGs was significantly increased following an increase in angular velocity (6→30→60 deg/s) in the soleus muscle. This suggests that the angle at the recruitment of motor units may be dependent on angular velocity in the soleus muscle.

PERSONAL SPACE PERCEPTION IN HUMANS / 体力科学

To examine personal space perception, a method of identifying joint position was determined by having the subject equally bisect the joint angle, by producing a minimum increment in change of position and by selecting a threshold for two-point discrimination using the metacarpophalangeal joint of digits 2-5.<BR>Eight healthy adults (6 males and 2 females) were used as subjects. The subjects' eyes were covered at all times to prevent any visual feedback.<BR>Each metacarpophalangeal joint of digits 2-5 was extended, flexed and pointed to the bisection position in 6 sec (about 2 sec in each position) . The difference in the bisection position selected using the index finger with the shoulder, elbow and hand in variety of positions was determined. The deviation from the mid-bisection point and the standard deviation were less when the hand was positioned most comfortably and near the face (“natural and near”) than when the hand was positioned in the more uncomfortable position and further from the face (“unnatural and further”) .<BR>In a second test, the index finger was moved from full extension to the full flexion in increments as small as possible at a rate of one change in position per second. Again, the effect of arm position was determined.<BR>In case of“the natural and near”position, each increment in joint position was smaller than in“the unnatural and further”position.<BR>In“the natural and near”position, the two point threshold was smallest of all. It was measured at the thumb side of right palm in the proximo-distal direction.<BR>These results suggest that personal space perception of metacarpophalangeal joint is affected by the position of adjoining limb segments.

Personal space perception in humans. Bisection and minimum division of the range of motion in finger joint, and the threshold for two-point discrimination / 体力科学

To examine personal space perception, a method of identifying joint position was determined by having the subject equally bisect the joint angle, by producing a minimum increment in change of position and by selecting a threshold for two-point discrimination using the metacarpophalangeal joint of digits 2-5.<BR>Eight healthy adults (6 males and 2 females) were used as subjects. The subjects' eyes were covered at all times to prevent any visual feedback.<BR>Each metacarpophalangeal joint of digits 2-5 was extended, flexed and pointed to the bisection position in 6 sec (about 2 sec in each position) . The difference in the bisection position selected using the index finger with the shoulder, elbow and hand in variety of positions was determined. The deviation from the mid-bisection point and the standard deviation were less when the hand was positioned most comfortably and near the face (“natural and near”) than when the hand was positioned in the more uncomfortable position and further from the face (“unnatural and further”) .<BR>In a second test, the index finger was moved from full extension to the full flexion in increments as small as possible at a rate of one change in position per second. Again, the effect of arm position was determined.<BR>In case of“the natural and near”position, each increment in joint position was smaller than in“the unnatural and further”position.<BR>In“the natural and near”position, the two point threshold was smallest of all. It was measured at the thumb side of right palm in the proximo-distal direction.<BR>These results suggest that personal space perception of metacarpophalangeal joint is affected by the position of adjoining limb segments.

THE VARIATION IN KNEE EXTENSION FORCE AND INTEGRATED ELECTROMYOGRAM WITH KNEE JOINT ANGLE IN SCHOOL CHILDREN / 体力科学

To examine the variation in the knee extension force and the integrated electromyogram from rectus femoris, medial vastus and lateral vastus muscles with the knee joint angle in growing children, measurements were conducted in 61 school boys aged from 7 to 12 years old. Anthropometric measurements were also done on the body height, the lower limb length, and so on. Results obtained were as follows.<BR>1) Ratio of the lower limb length comparing with the body height increased with the grade.<BR>2) Maximal force at each joint angle in each grade was shifted peak from 70°to 90°with the grade.<BR>3) The pattern of the integrated surface electromyogram from rectus femoris, medial vastus or lateral vastus muscle at each joint angle was the same in all of the grade. The integrated electromyogram at the maximal voluntary contraction was maximal at 45°of the knee joint angle in the rectus femoris muscle, at 110°in the medial vastus and at 90°in the lateral vastus muscle.

PERSONAL SPACE PERCEPTION IN HUMAN ELBOW JOINT / 体力科学

In order to examine the personal space perception, measurements were conducted on both elbows in 14 men and 46 women. Each subject, with his (or her) eyes closed and with his upper arm fixed horizontally, was instructed to stop the vertical and horizontal swing motion of his lower arm at the point he considered to be the middle of the range of possible motion on the front and side of plane at his shoulder, and this was repeated ten times. In various conditions, similar measurements were also done to study factors affecting the personal space perception in 14 men.<BR>Mean values of bisected angles in percentage against range of motion were deviated from the middle points in the direction of the elbow extension, although there were large differences between the individuals. The deviation was smallest in the vertical. side of plane, and was larger in the horizontal plane than that in the vertical plane. The deviation was not so much affected by the various conditions.<BR>It was suggested that the gain of the personal space perception is higher in the elbow extension than in the elbow flexion and its difference is larger in the horizontal plane than in vertical plane of the human elbow joint.

PERSONAL SPACE PERCEPTION IN HUMAN SHOULDER ON THE HORIZONTAL PLANE / 体力科学

To examine the personal space perception, measurements were conducted on both arms in 227 young men and women. Each subject, with his eyes closed, was instructed to stop the horizontal swing motion of his arm at the point he considered to be the middle of the range of possible motion on the horizontal plane, and this was repeated ten times.<BR>Mean values of bisected angles were deviated from the middle points in the direction of the horizontal adduction, although there were large differences between the individuals. The deviation was larger in the right arms than that in the left, and it increased with the increasing range of motion of the horizontal abduction.<BR>It was suggested that the gain of the personal space perception is higher in front of the body than in the side on the horizontal plane of the human shoulder.

RELATIONSHIP BETWEEN THE TWITCH TENSION CURVE AND DISCHARGE PATTERN IN SINGLE HUMAN MOTOR UNITS / 体力科学

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.

CHANGES IN CHARACTERISTICS OF RECRUITMENT MODES IN HUMAN MOTOR UNITS AT VOLUNTARY MUSCULAR RELAXATION / 体力科学

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.

CHARACTERIZATION OF MOTOR UNITS IN VOLUNTARY CONTRACTION / 体力科学

In order to examine variations in the recruitment order of motor units, voluntary contraction of <I>m. vastus medialis</I> was studied at various gradients of tension increase. Two inserted electrodes were used for the recording of spike discharges of two or three motor units. Spike discharges were recorded simultaneously with the value of tension of knee extension and with the integrated value of surface electromyograms (EMG) .<BR>The threshold value of a motor unit depended on the gradient <I>G</I> (kg/sec) of the tension increase. A similar change was also found in the latency time <I>T<SUB>l</SUB></I> (sec), where <I>T<SUB>l</SUB></I> is the time interval from the onset of EMG to the moment of recruitment of a motor unit. The relation <I>T<SUB>l</SUB></I> =ρ<I>G</I><SUP>-1+λ</SUP>X was experimentally found, where ρ is a proportional constant. The motor unit with a positive/negative value of λ is characterized to be static/phasic.

LONG PERIOD CONSTANCY OF THRESHOLD FORCE OF SINGLE MOTOR UNITS IN VOLUNTARY CONTRACTION AND ITS CHANGE INDUCED BY DESIRE FOR MICTURITION / 体力科学

In order to examine the characteristics of the activities of motor units over a long time, single spikes and consecutive discharges of single motor units were recorded by use of an inserted electrode. In addition, the tension at isometric contraction of knee extension or elbow flexion was simultaneously recorded. The results are summarized as follows.<BR>1) The relative threshold value of a single motor unit in <I>m. vastus medialis</I> stayed constant even for 13 hours. However, the threshold value increased with an increase in desire for micturition and returned to the original value upon disappearance of desire for micturition.<BR>2) It was observed in surface electromyograms of <I>m. rectus femoris</I> that both the amplitudes of potentials at the moment of single spike appearance and those corresponding to a constant sustained tension increased on raise of desire for micturition. Under the same circumstances, however, some motor units in <I>m. rectus femoris</I> showed an increase of, and the other motor units showed a decrease of, their relative threshold value.<BR>3) It was also found in <I>m. biceps brachii</I> that the relative threshold value of a single motor unit stayed constant for 6 hours. In this motor unit, no effect from the desire for micturition was observed.<BR>From these results, it can be presumed that each motor unit possesses a specific susceptibility for a long period. The relative threshold value, however, changed depending upon internal conditions such as desire for micturition. It can thus be concluded that the rotation of activity among the motor units is due to the variations of the relative threshold value.

THE STUDY ON THE CONDITIONS OF SUCCESS TO PROMOTE THE LONG DISTANCE RUN AND WALK TO THE UNTRAINED ADULT / 体力科学

Healthy male adults (22-58 years old) and female adults (21-49 years old) were tested on the influence by the long distance walking and running.<BR>6 males walked 50 km in 8 hours, 3 males walked 40 km in 7 hours, 2 females walked 50 km in 8 hours and a half hour, 4 females walked 35 km in 7 hours, and 5 females walked 20 km in 5 hours<BR>All participants were tested on their bloods, urines and blood pressures at the starting time, 5 min after the goal in, and one hour after the goal in. The results were as follows.<BR>1) Decrement tendency of the systolic and diastolic blood pressure were observed by the long distance walking.<BR>2) Degree of concentrations of the blood was not correlate with the distance of walking.<BR>3) Neutal white blood cells were increased in all groups, but 20 km walking female group. Lynphcytes were intensively decreased in all groups.<BR>4) Degree of increase of blood lactate, blood sugar and FFA did not relate the distance of walking.<BR>5) Increasing tendency of CPK and LDH were related to the walking distance, and that of CPK was more strictly.<BR>6) The increase of LDH isoenzyme 5 in all groups except 20 km female group may be caused by impressive muscle work. But it was noticed that the significant increase of LDH isoenzyme 1 were observed in the groups of female walked above 35 km and 50 km wilked male group.<BR>Further more 3 males were tested with 20 km walk, 13 and 20 km run. Above mentioned results we would like to propose that walking more than 20 km in female and 40 km in male and running more than 13 km in male should not be recommended imprudently.

MOTOR ABILITY CHARACTERISTICS OF THE URBAN ADULTS / 体力科学

Bulk of informations regarding the fitness researches indicates the general tendency of decrease of physical fitness level among urban adults, especially the middle and high ages. Development of simple and unsophisticated testing methods from which lower extremity fitness may be easily evaluated is a matter of urgent necessity. For this reason, the following test items were examined and proved to be valid for the testing purpose.<BR>1) Twisting strength against resistance at the hips by use of transducer apparatus<BR>2) Maximum height of single leg step up<BR>3) Maximum height of single leg step down<BR>4) Relationship between the height of chair from which the subject stands up without using upper extremities and the degree of trunk forward leaning<BR>5) Maximum time length of single leg stand while 80% body weight is loaded<BR>6) Foot dorsi flexion strength In addition, effect of daily training using some of the above mentioned tests was confirmed among middle and high age subjects.<BR>The characteristics of strength exertion was further studied in order to provide fundamental informations for the tests developed. Upon obtaining strength exertion pattern along with time course, a curve figure was constructed in which the difference between the maximum tension (Pmax) and tension recorded at arbitrary time (P), hence Pmax-P, was placed on the ordinate and the time by logarhythmic unit was placed on the abscissa. The strength curve, when demonstrated in this manner, was formed to be composed of three linear parts, indicating this recording method is useful in analyzing the characteristics of strength exertion.<BR>Whether performance drop curve during 30 seconds exercise may indicate 5 minutes endurance exercise was, then examined. The results indicated that repetitive muscular contractions for 30 seconds may be more valid than continuous contraction for 30 seconds in predicting muscular endurance of the middle and high age subjects.

STUDY ON THE EFFECT OF 25KM MARATHON TO THE BLOOD PRESSURE AND THE COMPONENTS OF URINE IN THE CASE OF AGED MEN / 体力科学

The aged above 40 to 76 years old ran 25 kirometers. We measured the systolic and diastolic blood pressure all of them before start and immediately after goal. The urine had been tested too. The results were as follows.<BR>1) The systolic and diastolic blood pressures measured at the point of immediately after goal were lower than that of before running in all aged groups markedly.<BR>Beside decreasing tendency of blood pressure, especially of systolic phase, due to running was higher in older people than younger.<BR>2) The excretion of albumin in urine was increased by the running in all age groups, but the degree of it was larger in younger group than older people.<BR>3) The number of people whose urine pH moved to acidity caused by running was much in the youngest group, and no one had been found in the oldest group.

STUDY ON THE PHYSICAL FITNESS OF AGED LONG DISTANCE RUNNER / 体力科学

Seven long distance runner aged from 51 to 75 were tested on the view point of physical fitness and results as follows.<BR>1) Mean values of maximum VO<SUB>2</SUB>ml/kg/min, maximum heart rate and maximum respiratory rate during all out running were 43.7, 170 and 56.4 respectively.<BR>2) The maximum heart rate, maximum respiratory rate and oxygen intake during 5 minutes walking with the speed of 120 meter/min. were 80 percent, 64 percent and 77 percent of the former respectively.<BR>3) A case that was able to run one hour under the condition the heart rate continued about 200 beats was found.<BR>4) The systolic blood pressures were rised during walking and running but were decreased below the level of starting time in 5 to 10 min. after the stop of them.<BR>5) It was presumed that the speed of initial stage of long distance running should be held relatively slow for the aged to perform their ability reasonavely.<BR>6) The girth of lower leg became large by the long distance running on the case of man, but not on the case of woman.<BR>7) The skinf old of them were reduced of all.<BR>8) Vital capacity ratio one second/max and side step test were high level, but the grip strength, vertical jump, backward flexibility, forward flexibility and static endurance of leg were not always high compared with ordinary level of same aged.<BR>9) The size of heart shade of them were almost appeared in the normal range.<BR>10) Anemia caused by hard training was found in all cases.

CERTAIN CHARACTERISTICS OF MOTOR UNITS OF ARM MUSCLES / 体力科学

In order to investigate certain characteristics of activity of motor units during strength control, discharges of single human motor units in the m. biceps brachii by use of electrodes inserted in the respective muscle were simultaneously recorded with tension developed at the elbow joint in its flexion effort. The results obtained were as follows :<BR>1) When analyzed from the relationship between mean discharge interval of motor unit and its standard deviation, unit of other type which may be classified as “intermediate” (named “M”) unit than kinetic (K) and tonic (T) units as classified by previous workers was also found to be similar to that of leg muscles.<BR>2) The tension produced by elbow flexion effort at the recruitment in a certain single motor units recorded in 15 seconds interval was also nearly constant during the 20 minute long experimental period which coincided with the result obtained in the case of leg muscles.<BR>3) On the relationship between mean relative threshold of motor unit and its standard deviation, while the T unit was found to be of low threshold value, the K and M units, recording higher values than the case of T unit in most occasions, showed wider range in its values. After analyzing the relationship between the values of T and K/M units by use of a diagram, standard deviation of relative threshold was found to be larger in relation to its given mean value in the dominant arm than the recessive. No significant differences were found in the size of error in attempting to continue certain muscular tension with control between the dominant and recessive arms.<BR>4) Statistically significant differences at 5% level confidence were found between different individual subjects in the frequency of single spike, appeared and recorded, ranging between 25.0-97.5 percent. The subject who showed higher single spike appearance frequency than the other was found to react significantly quickly in his single reaction time responding to photic stimulus (1% level) . Higher frequency of single unit spike appearance was observed in T unit than in K unit.

CERTAIN CHARACTERISTICS OF MOTOR UNITS IN ACTION IN RELATION WITH STRENGTH CONTROL MECHANISM IN MUSCLES / 体力科学

In order to clarify the voluntary strength control mechanism, certain characteristics of motor units were studied after series of recordings were simultaneously made on the discharge of single motor unit in the m. vastus medialis in its voluntary contraction by use of electrodes inserted in the respective muscle and the tension developed when attempting to extend the leg at the knee joint. The results obtained were as follows:<BR>1) When analyzed from the relationship between discharge interval and its standard deviation, unit of other type which may be classified as“intermediate”unit than kinetic and tonic units as previously classified, was found.<BR>2) The mean value of muscular tension was found to be proportionate with value of standard deviation, when tension made by recruitment of motor unit was measured by 15 seconds interval. While the K unit was found to be of low threshold value, T and M units were found to be of high values.<BR>3) No consistent relationship was found between the mean value of relative threshold and the frequency of single spike appearance, while K unit showed a tendency of smaller rate of single spike appearance than T unit.<BR>5) A decreasing tendency was generally observed in the mean value of relative threshold and its standard deviation, by loading isometric muscle tension of 2-10kg for 3-10 minutes. The rate of single spike appearance also deceased by same loading.

THE RELATIVE THRESHOLD OF ACTIVATION OF SINGLE HUMAN MOTOR UNITS IN VOLUNTARY MUSCULAR CONTRACTION / 体力科学

In order to investigate the mechanism of activity of motor units, discharges of single human motor units in the m. vastus medialis in voluntary contraction by use of electrodes inserted in the muscles were simultaneously recorded with the tension developed at the knee joint in its extension effort. The results were as follows.<BR>1) The single spike discharges of single motor units were observed at the rate of 54.5-86.2%, the total number of discharges being 100%, when the knee extension effort was gradually increased and was abruptly decreased by the time of spike wave appearance on the Braun tube.<BR>2) When the tension of knee extending force was maintained steadily, the longest consecutive discharge in a single motor unit was observed for more than 90 minutes.<BR>3) The tension of knee extending force at the recruitment in a certain single motor unit recorded in 15 seconds interval was nearly constant within 30-60 minutes tested with certain fixed value for each motor unit except some fluctuation.