Analyses of correlation function and Fourier transformation are one of the important tools in the investigation of biological phenomena. Since the method of these analyses had been applied for interpretation of surface electromyogram, isometric muscular contractions had been estimated easily and accurately. Reliability and validity of measured values had been acquired by the assistance of the electro-computer and statistology. On the assumption that generated processes of surface electromyogram of arm and leg were 1) probabilistic 2) stationary and 3) Gaussian, power spectrums of probability density functions of measured values, were calculated in X-Y charts.
As the results of the expeliment, following points were revealed.
1. For the estimation of surface electromyogram upon muscular isometric contractions, these analytical methods should be applied for physical fitness researches with reliability and validity of the results.
2. Upon the isometric muscular contraction, main discharge-frequency among surface electromyogram were existed in two bands of about 20 Hz and 90 Hz peaks.
3. In proportion to intensities of load (Kg), magnitude of the agonist's discharge was increased in the frequency-band of 90 Hz, and that of the antagonist's discharge also was increased in the frequency-band of 20 Hz.
4. According to these results, it was assumed that frequency-band of about 20 Hz would be corresponded with tonic muscular discharge and that of about 90 Hz would be equivalent to phasic muscular discharge.
5. The longer time of muscular contractions sustained, the wider the frequency-band of about 90 Hz became on account of mixed and interfered discharges of neighboring muscle groups.

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The purpose of this study is to elucidate the postural controlling mechanism in terms of the postural reflex.
The subjects standing upright on the “shift board” apparatus were subjected to an unexpected postural disturbance. The latent time of the neuromuscular activities was analyzed by the method of the EMG and the changes of the joint angles were analyzed by the electrogoniometer.
The following results were obtained,
1. The change of an ankle joint appeared just at the same time with the onset of the “shift board” movement, and the EMG activity of the tibialis anterior muscle appeared in the process of the extension of the ankle joint and “shift board” movement.
2. The change of the knee joint appeared after about 40 msec following the ankle joint. The change of the hip joint and the neck joint appeared thereafter but, the neuro-muscular activities of f he various parts of the body were activated by the “shift board” stimulus at the range of about 70-90 msec latency.
3. The postural controlling mechanism was discussed in relation to the theory of “simultanious combination”.
4. The trigger of the simultanious discharge of the EMGs was discussed.

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A somatometric study attempting to investigate the standard values for body density at adolescence was performed by densitometry in a series of seventy-four subjects, 47 males with a median age of 21.5±1.7 years and 27 females averaging in age at 20.1±1.1 years. And also a simple equation for the estimation of body density from measured skinfold thickness was investigated.
Results obtained were as follows:
1. The body density was determined to be 1.0750±0.0118 (mean±standard deviation) for men and 1.0428±0.0090 for women, respectively. The corresponding body fat contents (fat%) were 11.0±4.7% and 24.1±3.8%.
2. Various indices of physical construction, viz., relative body weight, Rohrer's index, Vervaeck index, Ponderal index and Hirata's index, were noted to show a generally close correlation with the body fat content determined by the densitometry, the correlation with Rohrer's index being most prominent.
3. Of the skinfold thickness in seven different regions of body surface (chest, abdomen, crista iliaca, upperarm, subscapular, thigh and buttock), that of the abdomen displayed the closest correlationship with the estimated body density in both men and women.
4. The circumference of various parts of the trunk and extremities such as the shoulders, chest, abdomen, hips, thight, brachial biceps, forearm, wrist, knee, gastrocnemius muscles or ankle was found notably less closely correlated with the body density in both sexes than the skinfold thickness was, thus indicating poor usefulness of these parameters.
5. Assessments were made as to goodness of fit between the body density estimated by the previously proposed equations and the measured values. The equation of Wilmore (r=0.825) showed the highest goodness of fit in men and that of Sloan (r=0.768) in females, respectively, indicating their reliably high accuracy.
6. Twenty-one different combinations of two each out of the seven regions of skinfold thickness measurement were analyzed for coefficients of their multiple correlation with the measured body density. In both males and females, the abdomen-thigh combination was noted to show the highest correlation coefficients.
The multiple regression equations for this pair of regions were formulated to be: Y=1.09482-0.00119 abdomen S, mm-0.00085 thigh S, mm for men, and Y=1.07028-0.00082 abdomen S, mm-0.00035 thigh S, mm for women.
Only four males (8.50) and a female (4%) exhibited differences over than 0.01 between the body density estimated be these equations and the measured value.
The results indicate noticeable accuracy of the estimation of body density by these equations which we believe are commendable.

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