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.
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.
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.
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.

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:
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.
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.
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.
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.

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.
1) The relative threshold value of a single motor unit in m. vastus medialis 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.
2) It was observed in surface electromyograms of m. rectus femoris 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 m. rectus femoris showed an increase of, and the other motor units showed a decrease of, their relative threshold value.
3) It was also found in m. biceps brachii 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.
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.

In order to examine variations in the recruitment order of motor units, voluntary contraction of m. vastus medialis 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) .
The threshold value of a motor unit depended on the gradient G (kg/sec) of the tension increase. A similar change was also found in the latency time T_l (sec), where T_l is the time interval from the onset of EMG to the moment of recruitment of a motor unit. The relation T_l =ρG^-1+λX 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.

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 :
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.
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.
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.
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.

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.
1) Twisting strength against resistance at the hips by use of transducer apparatus
2) Maximum height of single leg step up
3) Maximum height of single leg step down
4) Relationship between the height of chair from which the subject stands up without using upper extremities and the degree of trunk forward leaning
5) Maximum time length of single leg stand while 80% body weight is loaded
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.
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.
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.

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.
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
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.
1) Decrement tendency of the systolic and diastolic blood pressure were observed by the long distance walking.
2) Degree of concentrations of the blood was not correlate with the distance of walking.
3) Neutal white blood cells were increased in all groups, but 20 km walking female group. Lynphcytes were intensively decreased in all groups.
4) Degree of increase of blood lactate, blood sugar and FFA did not relate the distance of walking.
5) Increasing tendency of CPK and LDH were related to the walking distance, and that of CPK was more strictly.
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.
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.

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 ;
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.
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.
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.

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;
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.
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.
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.
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.