The objective of this study was to examine biological growth and development in skating performance by focusing on thigh muscle thickness and anaerobic power output capacity in Japanese speed skaters. One hundred thirty-three male and 96 female skaters aged from 10 to 22 years old were tested in this study. The anterior (MTA) and posterior (MTP) thicknesses of the thigh muscles were measured by the B-mode ultrasonic method. Maximal anaerobic power output capacity (MAP) was determined using a bicycle ergometer. The mean 500 m skating velocity (SV), calculated from recently attained individual best times, was used as a measure of skating performance. These parameters, along with height, were plotted on a logarithmic graph to obtain the allometric equation y=bx^a, where “a” is a growth index.There were two sharp bends in the graph showing the relationships between MTA, MTP, MAP, SV and body height in both males and females. The growth indexes “a” between the first and second changing points in all the above relationships were observed to be larger than the other phases. Ranges of body height between the first and second changing point in muscle thicknesses (MTA, MTP) ranged from 152.2-154.8 cm to 168.1-168.3 cm in males, and from 142.8-144.9 cm to 154.4-157.6 cm in females. The ranges of MAP were from 139.8 cm to 166.8 cm in males, and from 138.8 cm to 157.8 cm in females. However, the height ranges of SV were from 147.4 cm to 167.8 cm in males, and from 142.2 cm to 153.2 cm in females.From these results, it was suggested that accelerated development of skating performance and anaerobic power output capacity begins earlier than muscle structural development in speed skaters.

The purpose of this study was to investigate the relative growth of thigh muscle thickness and development of ball kicking performance in junior male soccer players.The study participants included 235 Japanese male soccer players aged between 10 and 18 years. Subjects were classified into 10 groups on the basis of their body height every 5 cm. The thickness of the anterior and posterior thigh muscles (MTA and MTP, respectively) were measured using B-mode ultrasonography. The ball distance (BD) and ball velocity (BV) were measured using a tape measure and a speed gun, respectively. By using a custom-made speed meter, we measured the maximal swing velocity of the lower limb (SV) while the players were kicking the ball. These parameters, along with the height, were plotted on a logarithmic graph to obtain the allometric equation y = bx^a.There was a sharp bend in the graph showing the relationships between MTA, MTP, BV, SV, and body height. The growth indexes "a" of MTA and MTP were increased at 157.3 cm and 159.9 cm, respectively. The development indexes "a" of BV and SV were increased at 144.3 cm and 146.1 cm, respectively. However, there were 2 sharp bends in the graph showing the relationships between BD and body height. The development index "a" of BD showed the highest value from 150.5 to 171.2 cm.These results suggested that the developmental spurt in ball kicking performance was faster than the growth spurt in muscle thickness of the thigh.

Muscle strength per unit muscle area related to age was investigated in normal 131 males and 127 females, 7 to 18 years of age. A cybex machine was used to measure the isometric muscle strength of elbow flexion and extension, knee flexion and extension, respectively. The cross-sectional muscle area of extensor and flexor at right upper arm and thigh were determined by using ultrasonic apparatus. The muscle area in male increased with age from 7 years to 17 or 18 years. Females showed increment in muscle area from 7 to 12 years for elbow flexor muscle, and from 7 to 16 years for another muscles. Muscle strength in both males and females increased with age from 7 to 16 or 17 years. Muscle strength per unit muscle area tended to increase with age in males from 7 to 12 years, and in girls 7 to 9 years except for elbow extension. The strength per area under 12 years of age for males and 9 years of age for females except for elbow extension were significantly lower than that of the above age. There were little differences in the strength per unit area with age among males from 13 to 18 years and females from 10 to 18 years, respectively. These results indicate that under 12 years for boys and 9 years for girls the increment in muscle area with age is not accompanied with the development of muscle function.

The aim of this study was to investigate the differences between male and female in the activity level of trunk and lower limb muscles during basic daily physical actions. Six young adult male and six female subjects performed 14 daily life actions, i. e. postural maintenance and change, and body weight transfer actions. The surface EMG of six muscles of the trunk and the lower limb was recorded using a portable electromyography apparatus. Maximal EMG response (EMG_max) during isometric maximal voluntary contraction for each muscle was used to normalize the EMG signal. In the performed actions, the average activity level of each muscle corresponded to 20% EMG_max or less in male and 30% EMG_max or less in female subjects, though there were some actions which exceeded 40% EMG_max in the soleus muscle. As a result of 3-way ANOVA, significant effects for each of the 3 factors (action, muscle and sex) for muscular activity level were recognized and there were significant interactions among each pair of factors. The mean activity level of leg muscles in actions which support and transfer body weight was significantly higher in females than males. In the case of identical actions, the total time taken to reach a high muscular activity level was longer in females than males. From these results, it can be assumed that the load on the lower limb muscles is larger for females than males in the case of supporting and transferring body weight in daily life.

The present study aimed to investigate the profiles of activities of thigh muscles during 100 m sprint running in track and field athletes experienced hamstrings (muscle) strain injury, with specific emphasis on the difference between injured and non-inured legs. The subjects were 20 track and field athletes who were divided into muscle strain injury group (MS) and non muscle strain injury group (NMS). The electromyograms (EMGs) of five thigh muscles (the biceps femoris, semitendinosus, rectus femoris, vastus lateralis and vastus medialis) and knee joint angles were recorded during 100 m sprint running. For NMS, there were no significant differences between the right and left legs. For MS, the averaged EMG of every muscle,expressed as relative to that during maximum voluntary contraction (%mEMG_MVC), values of the biceps femoris and semitendinosus in the latter phases of takeoff and swing periods were significantly higher in the injured leg than in the non-injured leg. Also, the maximal flexed and extended angles of the knee joint during takeoff and swing period, respectively, for the injured leg were significantly greater than those for non-injured leg. Thus, the present results indicate that track and field athletes experienced hamstrings (muscle) strain injury show by higher EMG activities in the biceps femoiris and semitendinosus of the injured leg at the later phases of swing and takeoff periods during 100 m sprint running. This may be partially related to the running style with a greater extended position of knee joint angles at the corresponding phases.

This study aimed to investigate the differences in the development of muscle thickness (MT) in the lower limbs with specific sports-event training. Furthermore, the relationship between MT of the lower limbs for weightlifters and sprinters and their competition performances (total weight lifted and 100m sprint times) was examined. Subjects were 64 males divided into 3 groups: weightlifters (n=20), sprinters (n=20), and untrained subjects as controls (n=24). The MT{relative to (body weight)^1/3}of knee extensors (KE), knee flexors (KF), plantar flexors (PF) and dorsi flexors (DF) was measured at 21 sites (proximal, middle and distal) along the length of the upper and lower leg by B-mode ultrasound. The MT of KE for weightlifters was significantly greater than that for sprinters and controls, while the MT of KF and PF for sprinters was significantly greater than that for weightlifters and controls. The MT of rectus femoris (RF), vastus intermedius (VI), vastus lateralis (VL) and vastus medialis (VM) for weightlifters was significantly greater than that for sprinters and controls, while the MT of RF and VM for sprinters was greater than that of controls. On the other hand, the MT of KE for weightlifters and sprinters (especially VM) correlated significantly with competition performances. These results indicated that squatting affected the MT of KE except for RF while sprinting affected the MT of KF and PF. It was also concluded that the MT of KE for weightlifters and sprinters (particularly VM) was related to their competition performances.

The purpose of the present study is to observe the accuracy of the ultrasonic A-mode method for measuring subcutaneous fat thickness. Nine healthy adults (4 males and 5 females) volunteered as experimental subjects. The skin and subcutaneous fat thickness at four different positions, the anterior, posterior, medialis and lateralis of the forearm, upper arm, leg and thigh, were measured by means of an A-mode ultrasonic subcutaneous fat caliper (CANON, CH 300-FT) and also by a B-mode method (ALOKA, SSD-120, ECHOVISION, Circular compound scanner) . Correlation coefficients of subcutaneous fat thickness between both ultrasonic methods were 0.808 for the forearm, 0.780 for the upper arm, 0.833 for the leg and 0.843 for the thigh with a statistical significance of 0.1 % level, respectively.
Differences of the thickness of subcutaneous fat between both methods were from 0.6 to 2.0mm as every absolute mean values. No significant differences were observed for mean subcutaneous fat thickness between both methods at each position. From these results, the A-mode ultrasonic method (CANON, CH 300-FT) is considered to be useful for measuring the thickness of skin and subcutaneous fat in human limbs.

The maximal isometric strength of the knee extension (KES) and cross-sectionl area of m. quadriceps femoris (MQF) were measured on 89 male Japanese elite athletes and 14 untrained men to evaluate the morphological and functional characteristics of athletes in the knee extensor muscles. Athletes were specialized in seven different sport events; 16 sumo wrestlers, 22 oarsmen, 8 volleyball players, 16 speed skaters, 12 association football plyers, 5 sprinters, 10 middle and long distance runners. KES was measured by using a specially designed straingages dynamometer at knee angle of 110 degrees (180 degrees= fully extended) . Cross-sectional area of MQF at the mid-thigh was determined by ultrasonic apparatus. The following results were obtained.
1. Sumo wrestters showed highest mean values (110.18 cm²) in MQF area among athlete groups. Lower mean values in MQF area were found in sprinters (86.34 cm²) and distance runners (73.86 cm²) whose values were not significantly different from that of untrained (75.32 cm²) .
2. In the cross-sectional area of each muscle bundle of MQF, sumo wrestlers, volleyball players and speed skaters showed higher mean values, and sprinters and distance runners had lower mean values as well as untrained men.
3. Higher mean values in percentage of MQF area to the total muscle area of thigh were observed in volleyball players (58.66%) and oarsmen (57.53%), lower mean value in association football players (53.81%), respectively. However, there were no significant differences in percentage of MQF area between untrained and each athlete group.
4. In the percentage of each muscle bundle area to MQF area, m. rectus femoris of association football players and m. vastus lateralis of speed skaters were significantly higher mean values compared with the untrained and other athlete groups.
5. KES were significantly related to the MQF area at 0.1% level (r=0.657) . There were significant relationships KES and each muscle bundle area in MQF area at 0.1% level. In the relationship between KES and each muscle bundle area, m. vastus lateralis showed the highest correlation coefficient (r=0.603) .
6. Association football players showed highest mean value (8.97 N/cm²) in KES per unit of MQF area among athlete groups. Its value was significantly higher than that of untrained men (8.06 N/cm²), distance runners (7.31 N/cm²), volleyball players (7.10N/cm²), and sumo wrestlers (7.50N/cm²) . There were no significant differences in KES per unit of MQF area intra athlete groups except for association football players.

The present study aimed to investigate the level of muscular activities such as postural mainte nance and change, and body weight transfer during daily physical activities, through electromyogram (EMG) recordings. In each of 27 prescribed movements, EMGs of a total of 8 muscles located in the upper arms, trunk and lower limbs were recorded in 12 young adult men and women using a port-able surface electromyograph apparatus. The percentage of integrated EMG per time (mEMG) to that during isometric maximum voluntary contraction (MVC) was calculated as an index by assessing the muscular activity level in each of the prescribed movements. In most of the prescribed movements, the muscular activity level of every muscle corresponded to about 20-30% of MVC, and tended to be higher in women than men. However, some actions induced an activity level of 40% and more of MVC in the soleus muscle. The activity levels of the lower limb muscles in going up and down stairs and a slope at a fast speed, and jogging were higher compared to other prescribed movements. Thus, the results indicate that body weight transfer actions in daily life raise the activities of the lower limb muscles to a level sufficient for maintaining and increasing their function.

To investigate the relationship between maximal aerobic power (VO₂max) and fatigu-abililty during repeated isokinetic contractions, 39 male speed skaters (mean 20.8 years) served as subjects. They were divided into two groups according to their VO₂max levels ; high VO₂max group (HI, n=19) and low VO₂max group (LO, n=20) . VO₂max was measured in all subjects during incremental exercise on a bicycle ergometer and body composition was determined by densitometry. Cross-sectional area (CSA) of the leg extensor muscles was evaluated using ultrasonic method. Fatiguability was assessed during the fatigue test consisting of 50 repeated isokinetic knee-extensions at an angular velocity of 180 deg⋅sec^-1. Remark-able findings include :
1. There were no significant differences in body composition and thigh composition between the two groups except for high subcutaneous fat in group LO.
2. There were significant differences in VO₂max between group HI (3.93l⋅min^-1, 67.3 ml⋅kg LBM^-1⋅min^-1) and group LO (3.59l⋅min^-1, 59.9 ml⋅kg LBM^-1⋅min^-1) .
3. In the fatigue test, the average initial values did not differ, however, the average final values were higher in group HI. Also, a significant difference was observed in per unit CSA between the two groups.
4. Higher peak forces (kg) in group HI were observed after the initial 30 dymanic contractions per unit CSA and % of peak values (% peak force) .
5. A close relationship was demonstrated between VO₂max per LBM and the fatigue index, i. e., the mean decline in peak force with 50 contractions (r=-0.37, p<0.05) .
Based on the present findings it is suggested that maximal aerobic power (VO₂max) influences the rate of fatigue development even during short-term maximal isokinetic contractions, and that there may be some physiological cross-linkages between cardiopulmonary regulation and the metabolic properties of skeletal muscles. This finding is also in conformity with earlier results indicating the importance of oxygen delivery as a limiting factor for muscle performance.