Muscle activity of human ankle extensors during ballistic plantar flexion movement was studied by use of the rubber-strain-gauge method. The muscle power was measured by using the after-loading method. The subjects quickly extended the ankle joint with loads of 20, 40 and 60% of the maximum voluntary contraction (MVC) of ankle extensor muscles.
Maximum muscle power was exerted at about the load of 60% MVC. This result can presumably be attributed to the increase in the recruitment and firing frequency of motor units in gastrocnemius muscle with each load attached to ankle extensors.
Although the amount of muscle power increased consistently with an increase in the calf girth immediately after an onset of load lifting (r=0.8479, p<0.001), the period in which it obtained maximum velocity was not significant. On the other hand, muscle activity immediately after onsets of load lifing are important and girth changes in muscle should be considered as parameter for estimating the power output of human muscles during ballitic contraction.

This study was designed to compare post-exercise hyperemia between ramp and ballistic contractions in human triceps surae. Subject was asked to extend ankle joint in range of 20 degrees for 1 sec and with maximum effort against loads of 10, 20, 30 or 40% of maximum voluntary contraction (MVC) in ankle extensors. Amount of post-exercise hyperemia was calculated from changes in calf girth recorded by using two strands mercury-in-rubber gauge.
1) Calf girth after contractions transiently decreased below precontraction level and increased gradually until its peak value, over precontraction level, in about 8 sec. Calf girth recovered to resting level for about 30 sec.
2) After ramp contractions, amount of decrease of calf volume increased in order to loads of 10, 20, 30 and 40% MVC, but was not so after ballistic contractions. Amount of its increase, excess precontraction level, depended on loads in both conditions. These values were below 1.0ml/100 ml tissue.
3) Amount of decrease of calf volume after ramp contraction was larger than that of ballistic contraction, but amount of its increase was inverse.
4) There was significant coefficient between calf volume increase after contraction and maximum inflow rate (ml/min/100 ml tissue) calculated from the maximum gradient in rising phase of calf girth (r=0.5508, p<0.001) .
From these results, it is suggested that“milking action”in muscle generate with ramp contraction, and that disturbance of pulsatile inflow to muscle and chemical and neuronal regulations to generate post-exercise hyperemia pronouncely act by ballistic contraction.

The purpose of this study is to investigate significance of transient decrease in sustained tension preceding rapid muscle contraction in elbow flexor muscles.
Before rapid voluntary contraction, steady forces below 20% of the maximum contraction were maintained, and each transient decreas was detected by using high sensitive strain gauge (FD pick-up) with EMG of brachial biceps and triceps muscles. And girth and length changes of the biceps brachii muscle with the tension decrease were detected by using rubber strain-gauge method and X-ray technique, respectively.
The following results were obtained
1) The transient decrease of steady forces were observed during the premotion silent period. Amount and duration of the transient tension decrease were below 20% of each steady force and 100 ms, respectively.
2) Amount of the transient tension decrease inversely correlated to time to half Pmax on the rapid tension development. (p<0.001)
3) Amount of the transient tension decrease was significantly coefficient with decrement of girth of upper arm. (p<0.001)
4) A distance between two Cu wire apexes inserted into biceps brachii muscle shortened with increment of muscle force.
These results suggest that before rapid muscle contraction stretch of biceps brachii muscle transiently occure, and that the stretch accelerate the following shortning velocity of the muscle via a stretch reflex.

I have reported that tension development of sustained tension transiently occur at volutnary muscle relaxation. I attempted to clarify relation of the transient tension development and velocity of muscle relaxation in brachial biceps muscle. Obtained results were as follows:
1) The tension followed with muscle relaxation was diphasic. Frequency of the diphasic tension increased depending on the sustained tension level before relaxation.
2) Amount and duration of the transient tension development were below 3% of the tensions and 80 ms, respectively.
3) There was significant relation between amount of the tension develovment and velocity of the muscle relaxation at the sustained tension of 15 (p<0.05) and 20%MVC (p<0.01) .
4) Girth of upper arm detected by using the rubber-strain-gauge method increased at the transient tension development.
From these results, it is suggested that the tension development is related to transient elevation of the central nervous activity and the muscle shortening during the transient tension development accelerated muscle relaxation by decrease of the spindle discharges in muscle.

I found that transient development in sustained tension occur before voluntarily, rapid muscle relaxation in elbow flexors and likely contribute to accelerate velocity of muscle relaxation. In this study, I attempted to clarify whether the transient development depended on contraction of phasic muscle.
Electromyograms and evoked potentials in gastrocnemius and soleus muscles were recorded respectively during the muscle relaxation of ankle extensors without flexor muscle contraction. The sustained tensions before muscle relaxation were 10, 20, and 30% of the maximum plantar flexion strength. The following results were obtained:
1) Frequency of appearance of the transient tension development was about 42% at 10% of the maximum plantar flexion strength, but decreased with the increase of the sustained tension.
2) On comparing between the velocity of muscle relaxation with and without the transient tension develoment, the former was significantly faster than the latter only at 10% of sustained tension. (p<0.001)
3) At the transient tension development H-reflex in gastrocnemius was potentiated, but inhibited in soleus muscle.
These results suggest that the transient tension development is due to contraction of the gastrocnemius muscle and inhibition of the activity of soleus muscle via a mechanism that excitation of PT cell evoke IPSPs in spinal slow α-motoneurons.

To clarify length changes of human muscle, forearm girth was recorded during various handgrips by using the rubber-strain-gauge method.
Subjects quickly lifted loads of 10, 20, 30% of the maximum grip strength (MVC) at a distance of 2 cm, and/or lifted and lowered those loads with the rhythm of 1 Hz.
In isometric condition, handgrip was performed with muscle strength for several seconds in the same conditions as the above. Fatiguing successive contraction was performed with muscle strength of 30% MVC for a few minutes.
1) During ballistic contraction of forearm flexors, differences between the onsets of its discharge and the increase in forearm girth were about 20 ms in all conditions. The increase in forearm girth occurred prior to the onset of the rise in the loads, and its extent depended on the loads.
2) In repetitive handgrips, changes of forearm girth in the muscle contraction phase were similar to those of the ballistic contractions. In the muscle relaxation, recovery of forearm girth to its resting level was delayed with increase of the loads.
3) Forearm girth during successive contraction for a short time remained at an approximately steady level, while its extent depended on the muscle strength. During fatiguing successive contraction, forearm girth gradually increased with an increase in muscle discharge.
These results suggest that length change in human muscle occures during muscle contraction in isometric conditions. Furthermore, this method is useful for the study of the human muscle shortening and lengthening, as to the muscle activity of concentric conditions and muscle relaxation process, even when there is no agreement of force-EMG relation.

Relaxation rate and contraction remainder of human forearm flexors following fatiguing repetitive handgrips were studied. These parameters were measured from the forearm girth and recorded by the use of a mercury-in-rubber gauge.
Subjects performed handgrips: Subjects lifted and lowered the load of 30% of the maximum grip strength at a distance of 2 cm with rhythm of 1 Hz.
1) During the muscle relaxations, the decrease rate of forearm girth in the falling period and/or the lowering stage of the load increased with repetition of handgrips.
2) The forearm girth at the onset of handgrip progressively increased.
3) Even after the handgrips, the resting forearm girth continued to increase for a few minutes, and then progressively decreased. But it did not completely recover its resting level even after 1 hr.
From these results, it is suggested that human muscles fatigued with repetitive contractions cause 'contraction remainder' in addition to the delay of muscle relaxation.

In the present report, significances of voluntary muscular relaxations were studied. Pattern of relaxation in elbow flexor muscles was examined in two conditions, with and without relaxation of contralateral muscles (Active Relaxation : AR, Passive Relaxation : PR, respectively) .
EMG patterns of biceps were obtained in various experimental conditions to investigate characteristics of each muscular relaxations. Arm flexor strength was exerted with saw-tooth and square forms produced by Low Frequency Generator, and in other case the strength was voluntarily exerted as fast as possible.
Muscular relaxation time was determined by the difference between begining of tension decrease and vanishing point of biceps spike discharge.
The results were ;
1) PR was faster than AR, but both relaxation times were prolonged following the increment of initial tension. There were no significant differences in the times between left and right arms, and between supine and prone positions of the forearm. Relaxation time in the square form muscular exertion was the fastest in AR.
2) Quickness of the biceps relaxation in PR was significantly correlated with the velocity of extensor muscular contraction. (r=0.41)
3) However, a transient excess tension development over the initial tension was observed at the initiation of relaxation in both conditions (less than 1 kg and 100 msec in most cases) . Both the excess tension produced and its duration were greater when the initial tension was higher. The rate of rise (g/msec) in PR was higher than AR.
These results suggested that each muscular relaxation in this study was conducted by different inhibitory systems. The inhibitory system in Active Relaxation might be localized in higher level of the central nervous system than that of Passive Relaxation

The purpose of this study is to investigate role of extension-flexion movement (Reactive Action) on exertion of flexor muscular strength in the upper arm.
There were three types in the reactive actions based on the different activities of flexor muscles. First type (Type I) was obtained when the load (1006 P₀, 30% P₀) applied in the flexor. Second type (Typ II) was obtained when the flexor started to contract after being quikly stretched. Third type (Type III) was obtained with the same manner as Type II, but flexor was stretched more slowly.
Effect of each type movements were compared its power and velocity with the results obtained by flexion movement (Control) from the same angle, which the elbow extended in 3 type movements.
1) The power was the largest in Type III, the ratio of reactive action/control was significant. (p<0.05)
2) In comparison the velocity in reactive action with it in control, Type II was faster.
3) These results suggest closed relationship between the flexor activity and the velocity in elbow extension. The each extension velocities was in order that, Type II, I and III.
4) Two kinds in the EMG of triceps were obserbed in Type II. One activated triceps in extension, but the other. But the extension velocity was slower the faster.
5) The characteristics of extension in all subjects were investigated by EMG during elbow extension. The EMG of extensor had two kinds as the same as Type II. During the relaxation, the extensor remained weak discharge in the subjects, who the extensor activity was recognized in Type II.
These results should suggest that there are different muscular activities in order to exert the power and velocitty.

In the present studies it was examined to begin with, whether intentional fixed quantity of exercise in response to previously defined level of heart rate could be loaded by treadmill connected with“Heart Rate Controller” (Quinton Co., Ltd.) i.e. a series of patterns in running exercise of the normal adult males were analysed.
The obtained results in short are in the following ;
1) Running exercise in response to previously defined level of heart rate being carried out by use of the above“Heart Rate Controler”, speed of treadmill needed to be adjusted manually until heart rate reached the defined level and then controlled automatically.
2) The relations between treadmill speed and heart rate defined at 130 Beats/min, 150 or 170 each, are as follows.
a) Treadmill speed at heart rate, previously defined as 130 B/min was 80±5-12 meters/min, actual heart rate during above exercise was 130±3-8 B/min in record.
b) Treadmill speed at heart rate, 150 B/min was 100±9-18 m/min, actual heart rate 150±6-8 B/min in record.
c) Treadmill speed at heart rate, 170 B/min was 130±10-33 m/min, actual heart rate 170±3-9 B/min in record.
As previously defined heart rate level was indreased, actual level in record deviated from the former within some extent and treadmill speed was also raised to maintain the defined heart rate level.
Fluctuation width of treadmill speed varied remarkably by the individuals.
Adjustment of treadmill speed was considered to be well under control by feedback mechanism of“Heart Rate Controller”.