In order to clarify the effect of exercise on the walking performance and the muscle volume in lower limbs, elderly athletes long continuing to be trained and untrained elderly were compared with regard to their muscle cross-sectional area (CSA) of m. psoas major, thigh muscle and crus muscle and their walking ability. The subjects used consisted of thirty-six 80's-aged male and 70's-aged female elderly athletes and twenty-four elders having no regular exercise (control male group : CM, control female group : CF) . The elderly athletes were further divided into two groups in accordance with their results of Japan Fitness Test (high performance male group : HPM, low performance male group : LPM, high performance female group : HPF, low performance female group : LPF) . The walking performance was evaluated by analyzing their walking speed, stride-length and step rate during walking along a 15 m-strip of passage at normal and fast paces using videotaping. The muscle CSA was determined at m. psoas major, thigh muscle (extensors and flexors) and crus muscle (m. tibialis anterior and m. triceps surae) using MRI. As for the walking speed and stride-length at the normal pace, only HPM and HPF showed significantly higher values than CM and CF (male : p<0.05, female : p<0.01) . Meanwhile at the faster pace, HPF and LPF showed significantly higher values than CF in female (HPF : p<0.01, LPF : p<0.05) and in the case of males, only HPM have a higher value only of the walking speed than CM (p<0.05) . The CSA of m. psoas major in HPM and HPF significantly higher than that in CM and CF (all p<0.05), while in CSAs of knee extensor muscles and m. triceps surae, the statistical differences were not consistent among male and female groups. The results suggested that greater muscle mass of m. psoas major could influence higher walking speed in elderly people, and might be affected by regular exercise training.

The purpose of this study was to prove the hypothesis that the effect of strength training is memorized and reinforced by retraining. Untrained university-age men participated in this training program. The retraining leg was subjected to 5 weeks of isometric training, 17 weeks of detraining and 5 weeks of retraining in knee extension. The contralateral training leg was subjected to 5 weeks of isometric training during the same period as the retraining phase of the retraining leg. Maximal isometric torque of knee extension increased after the 5-week training and remained at the trained level during the 17week detraining period. Torque gain by retraining of the retraining leg was 2.6 times greater than that of the contralateral training leg. These changes in isometric torque corres-ponded with changes in iEMG of the vastus lateralis. The cross-sectional area of the quadriceps femoris muscle did not change with training. Results support the hypothesis that the effect of strength training is memorized and reinforced by retraining. In addition, results show that these adaptations would be explained by recruitment and rate coding of motor units.

Effects of short-term, high-intensity and long-term, moderate-intensity exercise on biochemically assessed sarcoplasmic reticulum (SR) ATPase protein were analyzed in muscle homogenates of the rat after treadmill runs to exhaustion (avg, time to exhaustion 2 min 48 sec and 1 h 29 min, respectively) . The exercise-induced changes in SR Ca²⁺ -ATPase activity were muscle type-specific. After short-term exercise, a decrease in the activity occurred in the soleus muscle and the superficial region of the vastus lateralis muscle whereas long-term exercise depressed the rate of ATP hydrolysis in the soleus muscle and the deep region of the vastus lateralis muscle. The concentration of fluorescein isothiocyanate, a competitor at the ATP-binding site, for 50% inhibition of SR Ca²⁺ -ATPase activity fluctuated only in the soleus muscle subjected to short-term exercise ; it was increased by 31%. This change occurring in the soleus muscle would elevate SR Ca²⁺ -ATPase activity at a given concentration of ATP. The results presented here suggest that acute short-term exercise to exhaustion may exert a remarkably inhibitory factor on SR Ca²⁺ -ATPase protein of slow-twitch muscle, which can overcome the positive effect probably arising from the phosphorylation of the phospholamban.

We used near-infrared spectroscopy (NIRS) to study noninvasively the effects of aging on changes in muscle oxygenation during steady bicycle exercise. For the study, 6 healthy young males and 13 healthy elderly male volunteers were recruited. To evaluate the physical fitness level and to determine exercise intensity, the ventilatory threshold (VT) was first measured. As a result, elderly subjects were divided into two groups according to O₂ uptake at VT (Elderly-H ; 936.0±26.4, Elderly-L ; 695.3±29.9, Young ; 790.0±51.19 ml) . Secondly we measured muscle oxygenation by NIRS at rest and during exercise at relative work intensities of VT ; 20%, 40%, 60%, 80% and 100%. In all cases muscle oxygenation at rest and during exercise was expressed as a relative value from 100% oxygenation (oxygen capacity) established by thigh occlusion (ischemia) . All subjects showed progressive deoxygenation with increasing intensity. There were no differences between the three groups in muscle oxygenation during exercise at relative work intensity of VT. These data suggest that aging and physical fitness level have no effect on muscle oxygenation below relative work intensity of VT.

A study was conducted to clarify the effects of running intensity and duration of endurance training on myoglobin concentration ( [Mb] ) in rat skeletal muscles, and to clarify its temporal changes during the training. One hundred five male Wistar rats were divided into a training group and an untrained group. The training was carried out at 5 times a week for 12 weeks when the animals were 4 to 16 weeks of age. The training intensities were set at 20, 30 and 40 m/min with a duration of 60 min. The training duration was varied to 30, 60, 90 and 120 min when the rats were trained at 30 m/min. The temporal changes in the [Mb] were examined after the first, third and ninth week of training, during which the rats were trained at 40 m/min for 60 min per session. Three muscles (soleus: Sol, plantaris: P1, gastrocnemius-surface/deep: Gas-S, Gas-D) were analyzed for the [Mb] and citrate synthase activity (CS activity) . With regard to the intensity of training, the [Mb] increased with exercise intensity in Sol, Gas-D and P1, but not in Gas-S. P1 showed a greater increase of the [Mb] than Sol or Gas-D. On the other hand, CS activity in red muscle (Sol and Gas-D) increased even at low intensity, whereas white muscle (fast-twitch muscle: Pl and Gas-S) showed a significant increase in CS activity at an intensity of 40m/min. As to the duration of training, the [Mb] increased with the duration of running at 30 m/min of intensity, and showed the maximal adaptation with 90-min duration in all muscles except for Gas-S. Changes in CS activity according to the duration of running were similar to those for the [Mb] in all muscles. Finally, the [Mb] increased significantly with prolongation of the training period (after the 1 st, 3 rd and 9 th weeks training) in all muscles except Gas-S. However, the adaptive response of Mb tended to be delayed as compared with CS activity. These results suggest that 1) the response of Mb to training stimuli can depend on the muscle specificity (fiber type composition or the initial [Mb] ), and level of motor unit recruitment in usual, 2) Mb synthesis can be enhanced by an increase of training intensity, 3) a training duration of 90 min can bring out the Mb adaptation maximally and 4) the adaptive response of Mb would need more time as compared with CS activity.

The effects of running exercise on bone histomorphometric parameters were examined in sham-treated (Sham) and ovariectomized (OVX) rats. The rats were either kept sedentary (C) or trained (T) on a rodent treadmill at 25 m/min, 30 min/day, 5 days/week for 10 weeks. Fat-free dry bone weight, bone mineral content (BMC), and histomorphometric parameters were assessed after excision of the tibiae at sacrifice. The results are summarized as follows
1) There were no significant differences in fat-free dry bone weight and BMC between OVX-C and Sham-C rats. However, BMC/body weight in OVX-C rats was significantly lower than in Sham-C animals. OVX-C rats had significantly lower trabecular bone volume at the proximal tibial metaphysis than Sham-C animals. Values of bone formation parameters were significantly higher in OVX-C rats than in Sham-C animals.
2) BMC/body weight in OVX-T rats was significantly higher than in OVX-C animals. OVX-T rats had a significantly higher trabecular bone volume at the proximal tibial metaphysis than OVX-C animals. There were no significant differences in bone formation parameters between OVX-T and OVX-C rats.
3) No significant differences were found in any parameters between sham-C and Sham-T rats.
These results suggest that (1) running exercise has a suppressive effect on bone loss after OVX, and (2) training-induced reduction of bone loss by OVX does not seam to be associated with facilitation of bone formation but with suppression of bone resorption.

Using several electrophoretic techniques, this study examined the effects of 3 weeks hindlimb suspension on the patterns of isomyosins, myosin heavy chain (HC) isoforms and myosin light chain (LC) isoforms in the soleus muscle of the rat. The suspended soleus showed a shift in the HC isoform distribution with a marked increase in fast HC isoforms and a commensurate decrease in HCI. In addition, the change in the fast HC isoforms consisted of the expression of HCIId and HC IIb absent in the normal soleus. In contrast to HC isoforms, suspension did not lead to appreciable changes in LC isoform distribution. Analyses of electrophoresis under nondenaturing conditions demonstrated that the normal soleus expressing HCI and HCIIa isoforms contained two isomyooins. Although, of the two isomyosins observed in the normal soleus, the faster migrating band most likely represented the HCIIa-based one (FMas), its mobility was not identical with that of the HCIIa-based isomyosin (FMaf) found in fast-twitch muscles, migrating in the order FMaf>FMas. FMas was designated as intermediate isomyosin (IM) . Some of the suspended soleus contained slow isomyosin (SM) and IM whereas the others comprised FM 3 and/or FM 2 as well as SM and IM. In spite of the expression of HCIIb and HCIId in the suspended soleus, FM 3 and FM 2 observed in these muscles exhibited distinct mobilities from either HCIId-based or HCIIb-based isomyosins comprised in fast-twitch muscles. These results suggest that some of newly expressed HCIId and/or HCIIb isoforms in the suspended soleus are associated with not only fast but also slow LC isoforms and function as a constitutive element of the myosin molecule.

The effects of low- and high-intensity endurance training on the capillary network of rat left ventricle were studied morphometrically. Eighteen male albino rats of Wistar strain (4-wk-old) were assigned at random to a sedentary control group (Cont, n=8) and two trained groups which were both subjected to exercise on a motor-driven treadmill for 60 min a day, 5 days/wk for 9 weeks from 7 wks to 16 wks of age with different running speed; the low-intensity trained group (T-20, n=5) ran at 20 m/min and the high-intensity trained group (T-40, n=5) at 40 m/min. All morphometric parameters for the capillary and muscle fiber were determined in perfusion-fixed hearts. After the training period, the average muscle fiber cross-sectional area in the T-20 and the T-40 was not significantly different from the Cont. There were no significant differences in the capillary density and the capillary-to-fiber ratio between any groups, suggesting no significant change in capillary number. On the other hand, the number of capillary with large luminal diameter (8-10 μm) in the T-40 but not the T-20 was significantly greater than the Cont. These results indicate that the high-intensity endurance training causes enlargement of the capillary luminal area, while neither the low-nor the high-intesnity endurance training stimulate the proliferation of capillaries in the left ventriclular myocardium. In conclusion, a structure of the capillary network of rat left ventricle responds to the high-intensity endurance training by enlarging capillary luminal area rather than by increasing capillary number.

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.

The present study was designed to determine whether conversion of fiber types (type I to II) induced by hindlimb unloading (HU) is identical along the length of fibers in the soleus (SOL) muscle. After 1 and 2 wk HU, SOL was divided into three (proximal, middle and distal) regions and the fiber type composition was determined using myosin adenosinetriphosphatase (ATPase) . There was no significant change in fiber type distribution after 1 wk of HU. The percentage of type I fibers significantly decreased in the proximal and middle regions and that of type IIc fibers increased in all regions after 2 wk of HU. The percentage of type IIc fibers greatly increased in the proximal and middle regions compared with the distal region. Serial cross-sections every 300μm were processed for myosin ATPase from the middle to the distal region, and then analyzed to show the differences in staining characteristics along the length of single fibers. After 2 wk of HU, some of the fibers (3.1±1.2%) displayed changes in the staining characteristics of myosin ATPase (pH 10.3) ; 84% of these fibers identified type IIc fibers in the middle region were observed as type I fibers in the distal region. These results suggest that muscle fibers in unloaded SOL may not transform synchronously or uniformly along their length