The physiological cross-sectional area (PCSA) of knee extensors (KE) and flexors (KF) was determined using magnetic resonance imaging (MRI) in humans. Twenty two healthy male volunteers were assigned to the subjects and MRI was taken to obtained 41-52 consecutive axial images (slice thickness ; 10 mm, interslice gap ; 0 mm) from right-leg thigh. From these images, anatomical cross-sectional area (ACSA) of KE and KF was determined. Muscle volume was calculated from the summation of each ACSA and the distance between each section. Muscle length was determined as the distance from most proximal to most distal images in which the muscle visible. The PCSA of each muscle was calculated as muscle volume times the cosine of the angle of fiber pinnation divided by fiber length, where published fiber length : muscle length ratio were used to estimate fiber length. The isokinetic knee extension and flexion (angular velocity ; 30, 60, 180, 300, 450 deg/sec) was measured to estimate the muscle force at KE and KF. Specific tension of KE and KF was calculated muscle force deviled by PCSA. The mean muscle volume of KE and KF was 2178, 1141 cm³. The ratio of KE : KF was 2.6. The mean fiber length in KE was 7-8 cm, and in KF was 6-42 cm. Peak torque during knee extension was significantly higher than knee flexion at all angular velocities. The specific tension of KF was higher than that of KE at all tendon velocities. Moreover, relationships between specific tension and tendon velocity/fiber length, KF was still higher than that of KE. These results suggest that the capacity of tension development differ between KE and KF under the same shortening velocity per unit of sarcomere.

The relationship between relaxation time and muscle fiber composition was investigated in 16 males.
A highly positive correlation was found between muscle fiber composition and relaxation time. In addition, higher proportions of fast-twitch fibers were associated with longer relaxation times, indicating that the fast-twitch fiber has a longer relaxation time than the slow-twitch fiber.
Multiple regression analysis, which was conducted to investigate the suitability of relaxation time as a model for estimating muscle fiber composition, revealed that the T 1 and T 2 were significantly related to muscle fiber composition.
Therefore, the results of the present study indicate that relaxation time obtained by MRI can be used to estimate muscle fiber composition.

To evaluate the changes in muscle energetics following NaHCO₃ intake, we measured the phosphorus-31 nuclear magnetic resonance (³¹P NMR) spectra of human muscle in vivo during exercise. Seven male subjects performed two trials, a NaHCO₃ (Alka, Tr.) and a NaCI trial (Cont. Tr.), on two occasions. ³¹P NMR spectra were obtained serially during leg-elevating exercises. Before and during exercise, the intracellular phosphocreatine (PCr), inorganic phosphate (Pi) and pH were determined from the NMR spectra. The decrease of intracellular pH during exercise showed a tendency to be inhibited by NaHCO₃ intake, and the intracellular pH at the end of the exercise was 6.69 for Alka. Tr, and 6.51 for Cont. Tr. The decline of the PCr/ (PCr+Pi) ratio during exercise was not influenced by NaHCO₃ intake. The PCr/ (PCr+Pi) ratio was related exponentially to the intracellular pH. A remarkable decline of PCr/ (PCr+Pi) ratio occurred until the intracellular pH fell to about 6.7, but did not decrease below that. It was suggested that the intake of NaHCO₃ could decrease the rate of fall in the intracellular pH during exercise, and that the PCr store could be influenced by the intracellular pH when the pH was above 6.7, but not below that level.

A study was conducted to investigate using ³¹P NMR the relationship between the total excess volume of CO₂ output (CO₂ excess) due to bicarbonate buffering of lactic acid produced in exercise and the decrease of intracellular pH during incremental exercise. Five sprinters and 5 joggers performed incremental exercise to exhaustion on an bicycle ergometer. The values of CO₂ excess and CO₂ excess per body weight (CO₂ excess/W) were not different between the sprinters (2388±659ml, 36.7±8.5 ml·kg^-1) and the joggers (2275±278ml, 40.0±6, 3ml·kg^-1) . Below the ventilatory threshold (VT), from VT to the respiratory compensation point (RCP), and above RCP, the V_od2-V_co2 slopes were not different between the sprinters and the joggers, respectively (0.95±0.05 vs 0.95±0.06, 1.21±0.11 vs 1.30±0.14, 1.69±0.24 vs 1.76±0.18) . However, the joggers showed significantly higher CO₂ excess/W per blood lactate accumulation (ΔLa) in exercise (CO₂ excess/W/ΔLa, 5.34±0.32ml·kg^-1·mmol^-1·l^-1) than the sprinters (4.50±0.14ml·kg^-1·mmol^-1·l^-1) . The decrement of intracellular pH during incremental exercise showed a tendency to be smaller in joggers (0.63±0.18 pH unit) than in sprinters (0.83±0.10 pH unit), although there was no significant difference between the two groups. The values of CO₂ excess/W/ΔLa were correlated with the decrease of intracellular pH (r=-0.792, p<0.01) . It is suggested that CO₂ excess/W/ΔLa reflects the efficiency of the bicarbonate buffering system, and could be an important factor influencing the decrease of intracellular pH due to lactate production.

In this study, the effect of moderate endurance training on muscle morphological properties of human thigh muscles and isokinetic strength was examined. Five sedentary females carried out a training program of 30 min./day, 3 times a week for a ten-week period. The load requirement was set to 60% of maximal aerobic capacity (Vo₂max) of the subjects. In the determination of muscle cross-sectional areas (CSAs) by MRI, longitudinal sections were first imaged, and ten axial images along the length of femur were taken before and after the endurance training. Muscle CSA and mus-cle volume of knee extensors (KE), flexors (KF), and adductors (AD) were calculated, using the ten axial images. Vo₂max was significantly increased after endurance training (14.6%, p<0.01) . Muscle CSA in KE was significantly increased at the ten levels of femur length. There were also significant increases at seven levels of femur length after endurance training in KF (p<0.05, and 0.01) . Percentage increase of msucle CSA in KE and KF were 10.9 to 16.5% and 7.7 to 15.8%, respectively. Although the muscle volume of KE, KF, and AD was significantly increased, no change in fat volume was observed after endurance training. Isokinetic knee extension and flexion peak torque and peak torque per unit of muscle CSA at three angular velocities (30, 180, and 300 deg/sec) didn't show significant changes. These results suggest that muscle hypertrophy induced by moderate endurance training has no effect on muscle strength.

In this study, the effect of moderate endurance training on muscle morphological properties of human thigh muscles and isokinetic strength was examined. Five sedentary females carried out a training program of 30 min./day, 3 times a week for a ten-week period. The load requirement was set to 60% of maximal aerobic capacity (Vo₂max) of the subjects. In the determination of muscle cross-sectional areas (CSAs) by MRI, longitudinal sections were first imaged, and ten axial images along the length of femur were taken before and after the endurance training. Muscle CSA and mus-cle volume of knee extensors (KE), flexors (KF), and adductors (AD) were calculated, using the ten axial images. Vo₂max was significantly increased after endurance training (14.6%, p<0.01) . Muscle CSA in KE was significantly increased at the ten levels of femur length. There were also significant increases at seven levels of femur length after endurance training in KF (p<0.05, and 0.01) . Percentage increase of msucle CSA in KE and KF were 10.9 to 16.5% and 7.7 to 15.8%, respectively. Although the muscle volume of KE, KF, and AD was significantly increased, no change in fat volume was observed after endurance training. Isokinetic knee extension and flexion peak torque and peak torque per unit of muscle CSA at three angular velocities (30, 180, and 300 deg/sec) didn't show significant changes. These results suggest that muscle hypertrophy induced by moderate endurance training has no effect on muscle strength.

We investigated the muscle energetics using ³¹P nuclear magnetic resonance (³¹P NMR) spectroscopy, muscle cross-sectional area by magnetic resonance imaging (MRI), isokinetic strength, maximal anaerobic power and 40-sec maximal cycling test (40 seconds power) in All Japan soccer players (JPN: n=6), Olympic and Youth representatives (OL: n=6), and Japan Soccer League players (JSL: n=5) . There was no significant difference in muscle energy metabolism measured by ³¹P NMR between the JPN and the OL or JSL players at rest, during exercise, or in the recovery period. The total muscle cross-sectional area was significantly larger in the JPN players than in the OL players at the upper (70%) and the middle (50%) parts of the thigh (p<0.05) and than in the JSL players in the upper (p<0.01), middle (p< 0.05), and lower (30%) parts (p<0.01) . The isokinetic strength in left leg extension at 180 deg/sec was significantly greater in the JPN players than in the OL players (p<0.05) . Muscle strength was also greater in extension of both legs at 450 deg/sec (left p<0.05, right p<0.01) in the JPN players than in the JSL players. The maximum anaerobic power was significantly greater in the JPN players than in the OL players (p<0.05) and the JSL players (p<0.05), and the anaerobic power per kilogram of body weight was significantly higher in the JPN players than in the JSL players (p<0.01) . There was no significant difference in the 40 seconds power among the three groups. These results suggest that the JPN players have greater muscle power than the OL or JSL players because of the differences in the muscle mass.

According to cross-sectional studies, decreased postural stability, assessed by center of pressure (COP) sway, has been remarkable over the past 60 years, and has become one of the impairment factors for quality of life in the elderly. In the present study, in order to determine whether exercise training, consisting of bicycle ergometer and strength training inhibits decreased postural stability for elderly individuals (60 years of age or more), we investigated changes in COP sway and plantar flexors muscle volume. Healthy male (n=9) and female (n=8) subjects aged 62 to 76 yrs participated in the present study. Subjects were requested to maintain a quiet standing barefoot position on a force platform (type 9281B, Kistler) with their eyes opened or closed. Mean velocity of COP (COP sway length/time) was calculated from anterior-posterior COP sway from force platform data. From the spectral analysis of COP sway, low (0-1 Hz) and high (1 -10 Hz) frequency components of COP series were extracted. The muscle volume of the plantar flexors muscle group was estimated from multi-regression analysis based on measured muscle thickness at the lower leg posterior site using an ultrasonographic apparatus (SSD-500, Aloka) . Mean velocity of COP significantly (P< 0.05) decreased due to training, and this was accompanied by a decrease in COP sway high frequency components. On the other hand, COP sway low frequency components and muscle volume did not change. These findings suggest that an inhibition of decreased postural stability in the elderly is not mainly related to muscle volume, but to improvement of a feedback system from somatosensory function. With respect to the elderly, who have a larger mean velocity of COP, however, postural stability could be related to muscle volume.

The purpose of this study was to confirm the causal structure model of muscle, motor and living functions utilizing structural equation modeling (SEM) . As subjects, 103 community-dwelling older men and women, aged 65.7±6.9years of age, participated in the study to measure muscle cross-sectional area, maximum voluntary contractions, muscle power, 4 physical performance tests, and 16 questionnaires regarding ability of activities of daily living. The causal structure model of muscle, motor and living functions was hypothesized to be a hierarchical causal structure. The causal structure model of muscle function was hypothesized to be a hierarchical causal structure consisting of 3 sub-domains of muscle mass, muscle strength, and muscle power. Data analysis procedures were as follows : a) testing of construct validity of muscle function variables using confirmatory factor analysis (CFA) in SEM ; b) testing of causal structure using SEM ; c) testing of factor invariance using multi-group analysis for gender. The highest goodness of fit indices was obtained in the causal structure model of muscle, motor and living functions (NFI= .928, CFI= .978, RMSEA =.061) . The causal coefficient of muscle function to motor function was .98 (p<.05), followed by.34 for motor function to living function. From the results of multi-group analysis, the measurement invariance model indicated the highest goodness of fit indices (TLI=.968, CFI .977) . It was concluded that the hierarchical causal relation was among muscle, motor and living functions, and in which muscle function was consisted of 3 sub-domains.