The present study examined the recruitment threshold of motor units (MUs) and the cold reflex activation of the cutaneous receptors at the first turning point (TP1) and the second turning point (TP2) of decreasing skin temperature. The skin temperatures of the biceps brachii were continuously reduced using a cooling chamber fixed at -10°C. TP1 and TP2 appeared at 25.5±0.5°C and 18.5±2.21°C, respectively. The data were collected at±1°C of TP1 and TP2 (TP1-B, TP1-A, TP2-B and TP2-A) . The MUs was collected during a slow ramp contraction for 3 sec to 20% maximal voluntary contraction (20%MVC) at the each measure points (TE) . The rates of decrease in skin temperature were 1.242±0.349°C min at slope-1 (TP1-B), 0.627±0.284°C rain at slope-2 (TP1-A and TP2-B), and 0.201±0.045°C/min at slope-3 (TP2-A) . The difference of the threshold force value (ΔTF= TE-control value) of LT-MUs were positive value, on the other hand, ΔF of HT-MUs were negative value at TP1-B, TP1-A, TP2-B and TP2-A. The changes of ΔTF of LT-MUs were a little at TP1-B, TP1-A, TP2-B, and increased markedly more at TP2-A than at TP1-B (p<0.05) . On the other hand, the ΔTF of HT-MUs decreased significantly more at TP1-B than at TP1-A and TP2-B (p<0.05), however, it did not significantly differ at TP2-A. These results suggested that the threshold force of HT-MUs depend on skin temperature and LT-MUs depend on decrease speed of skin temperature.

Vigorous exercise induces a muscular oxidative DNA damage due to increased generation of reactive oxygen species (ROS). However, it is not fully understood how ROS induces muscular DNA damage after vigorous exercise. This study examined the relation between muscle damage and the muscular oxidative DNA damage in the gastrocnemius (GAS) and soleus (SOL) muscles of rats after eccentric exercise. All rats performed level (0 degree ; L) or downhill (—17 degrees ; DH) running on a treadmill for 1h at 20 m/min. In GAS, the 8-hydroxy-2'-deoxyguanosine (8-OHdG) content, an indicator of DNA damage, showed a 2-3 times increase from that in the control after DH running, but not after L running (P<0.05). The 8-OHdG content was positively correlated with lipid peroxide (TBARS) (r=0.61, P<0.01). Moreover, plasma creatine kinase (CK) activity was positively correlated with 8-OHdG content (r=0.68, P<0.05) and TBARS (r=0.64, P<0.05) after both DH and L running. The 8-OHdG content in SOL showed larger changes than that in GAS during the 1-week recovery period following DH running. These findings show that the exercise-induced muscular DNA damage is reflected in plasma CK activity. Consequently, it is suggested that changes in plasma CK activity can also be useful as an indicator of muscular DNA damage.

A small amount of the myotube-like structures (chained nuclei) are present in skeletal muscle independently of disease. These experiments show that the incidence of the myotube-like structure increases with the advance of age in mice. Moreover, it is shown that the DNA in the myotube-like structure is not fragmented. That is, the myotube-like structures were TUNEL (Terminal deoxynuc-leotidyl transferase (TdT) -mediated dUTP-biotin Nick-End labeling) negative. Moreover, we detected the polyadenylated mRNA around the myotube-like structure by using an in situ hybridization technique. This suggests that the myotube-like structure has transcription activity.
This report indicates that the myotube-like structure is a useful indicator of aging in skeletal muscle.

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.

Analytical method of correlation function and Fourier transformation has been applied for surface electromyogram. This study is to be aimed to investigate relation between motor-activities in isotonic muscular contractions and frequency in muscular electric discharge. By help of digital electrical computer, frequency characteristics in isotonic contraction of M. Biceps Brachii and M. Rectus Femoris have been calculated as Power Spectrum Density clearly and quantitatively.
As the result of this study, following points were revealed.
1) Fourier transformation was cleared up as the available method of physical fitness research in interpretation of surface electromyogram, on the assumption whose phenome-non was stationary in the process of statistical probability.
2) Upon isotonic contraction, high and low frequency bands were divided distinctly among muscular discharge of surface electromyogram, that were about 20Hz and 75-90 Hz bands.
3) In proportion to intensities of load and to alteration of movement velocity, high discharge frequency band showed changes of ranges of ±15Hz, but low discharge frequency band showed no change.
4) In high discharge frequency band, density of Power Spectrum of M. Biceps Brachii was larger than that of M. Rectus Femoris, but on the other hand of low dis-charge frequency band, this Power Spectrum displayed no difference between both muscles.
5) Comparing with two sorts of muscular contraction, that were isotonic and isometric, high discharge frequency band of the former was higher about 10Hz than that of the later.
6) It was supposed that this low frequency band was dependent upon tonic Neuro Muscular Units and was corresponding to slow contraction of red-colored muscles.
7) It was considered that this high frequency band depended on phasic N.M.U. and had connection with quick contraction of pale-colored muscles.

The purpose of this study is to clarify the characteristics of the short-term motor-memory and to analyze various loads effect of motor-retention in the exercise of flexion and extension of the fore-arm. As the means of analysis, correlation function between command and response waves was used efficiently and furthermore the electric computer system helped to investigate motor-retention. Many experimental conditions were decided to 0.1-0.8 Hz of one's exercise rhythm, 0-0.5 kg of loads attached to the fore-arm, and 3-6 cm of exercise displacement. Three healthy persons were employed as subjects.
As the results of this study, following points were shown clearly.
(1) After the fore-arm was exercised to the flexuous and extensional directions for 25 sec., response waves of motor-retention were recorded to Data-recorders for 60 sec Quantitative analysis of this motor-retention became effective by using the method of correlation function.
(2) About exercise rhythm (frequency), the rapidity of fore-arm exercises in the retentive learning was 0.05 Hz slower than that of these exercises in the begining learning.
(3) About the transfer gain of these exercises between command and response waves, two motor-gains of the retentive and begining learning were shown the same values only when these exercises were practised at experimental conditions of 0.8 Hz frequency and 0.5 kg load.
(4) Motor-retention rate, that was calculated from error values of performance, was dropped down such as about 0.3 rate in proportion to the time elapsed of recollection and also to rhythm-slownes of the command frequency.
(5) Optimal exercise displacement of the fore-arm was proved to the median of 6 and 3 cm in order to reappear the length memorized by the begining learning.
(6) Discharged voltages of the integrated EMG in Flexor and Extensor C arpi Radialis were recorded lower at the time, when motor-retention was displayed rightly and exactly.
(7) Sychological reminiscence and this motor-retention were shown quite opposite results in the learning points of reaction time, rhythm, strength and displacement, because the former was dependent upon the memory in the central nervous system (brain cortex), while the latter relied upon the memory in the peripheral-nervous system (receptor) .

The impulsive force-external loads relationships are reported experimentally on eight adult males by the method providing different actions : soft and hard motion or attached spring on the platform, four jumping down heights of the stand : 15, 33, 67 and 125cm and four additional loads to the body weight : 1, 2, 4 and 8kg. The forces are dealed with as the momentum on the landing motion and apparatus used are multi-component forces plate and 16mm camera. The impulsive force is measured using the planimeter about recorded waves of multicomponent forces exerted in the landing motion over the time of 0.8sec. The results obtained are as follows ;
1) The impulssive forces are increased on the relation of the logalithmic function proportionally with the height of stand and with the weight of load.
2) According to analyses of the landing motion, these angles of the ankle, the knee and the hip are flexed greater in proportion to heigher of the stand but no changes of these angles of body segments are showed with weighter of additional loads.
3) Taking these results and reference into consideration, absorbable landing motion has been assumed to involve decrement oscillation in internal body segments and to maintain potential using for the next motion.

Neuromuscular fatigability of different muscle groups was studied under various physiological conditions in eight healthy male subjects by means of EMG fatigue curve analysis (E/F ratio defined as the rate of rise in IEMG/force as a function of time) which has been commonly used.
Under the experimental conditions and assumptions described in the present investigation, the following conclusions could be justified on the basis of the experimental results.
1. The E/F ratio for the biceps brachii muscle was significantly greater (p<0.0005) than that of the soleus muscle at 40% of MVC, suggesting that the biceps brachii with presumably greater %FT fibers were consistantly more fatigable than their own soleus muscle.
2. The exponential growth of the E/F ratio as a function of either the maximal sustaining time (T_s) or different fractions of MVC suggested a possible neurophysiological link between the fatigability of the biceps brachii muscle and their MU activities which might increase in an accelerated fashion.
3. The evaluation of static work capacity (W_s) described in the present study revealed that the differences in the critical force level and Ws during free circulation and arterial occlusion could be explained by the relative availability of muscle blood flow which might determine the rate of energy reconstitution.
4. The EMG data taken during a constant torque output on an electrically braked bicycle ergometer indicated that some shift in the MU recruitment and/or MU firing frequency may occur during the application of arterial occlusion causing local muscle hypoxia.

The purpose of this study was to examine the effect of the different visual and vestibular inputs on EMG response of ankle muscles during movement to absorb impact in sliding down a slope. Thereby, our research focused on the relationship between preactivation (PA) in central program and stretch reflex induced by dorsiflexion immediately after impact. The subjects were nine healthy males. Movements were conducted using a special sliding apparatus. Conditions included sliding down a lower 15°slope with eyes open (Low) and with eyes closed (Low-Closed), and a higher 20°slope with eyes open (High) . PA prior to impact indicated the co-contraction of the medial gastrocnemius (MG) and tibialis anterior (TA) . PA levels in those muscles were significantly higher during High than during Low-Closed (p<0.05) . In contrast, PA of the coleus (Sol) was low in all test conditions. After impact, however, the stretch reflex of Sol during Low-Closed was greater than other test conditions. Because muscle stretch velocities and PA levels of Sol among all test conditions remained unchanged, these results suggest that different visual inputs could change the response of stretch reflex by modulations in reflex gain.

The present studies were performed to investigate changes of reaction time and increase of muscle strength by isometric training of biceps brachii muscle. The intensity of its training was the three types of maximal voluntary contraction (MVC), 70%MVC and 50%MVC. EMG reaction time (EMG-RT) as a function of motor control in center nervous system was measured by isometric contraction on fixed elbow.
After training for 8 weeks period, integrated EMG (IEMG) and power spectorum (mean power frequency, MPF) were increased as a component of muscle strength. IEMG and MPF were increased 83.6% and 16.6% in MVC training group, and were increased 86.2% and 20.8% in 70%MVC training group, and were increased 69.2% and 13.2% in 50%MVC training group. Increase of muscle strength in MVC, 70%MVC and 50%MVC training group increased 36.8%, 42, 3% and 30.6%, respectively. Consequently, decrease of EMG-RT was markdly associated with increase of muscle strength. The heavy intensity of isometric training, MVC and 70%MVC groups, decreased the EMG-RT greater than 50%MVC training group. Therefore, the decrease of training-induced EMG-RT correlated to development of muscle strength due to stimulation by training intensity. These results suggest that the decreased EMG-RT might be due to stimulation on motor central system by muscle training of heavy intensity.