The purpose of this study was to determine whether short duration stretching is ameliorating for disuse muscle atrophy in immobilized rat soleus muscles. Eighteen male Wistar rats (age, 8 weeks; weight, 311.0 ± 35.6 g) were divided randomly into control (n=3) and experimental (n=15) groups. Bilateral ankles of each rat in the experimental group were fixed in full planter flexion with a plaster cast. After the experimental groups rats were immobilized for 4 weeks, animals were divided into three groups: immobilization alone (group I, n=3), stretch training for 30 min/day for 1 or 3 weeks after remobilization (group S, n=6), and spontaneous recovery (non stretch training) for 1 or 3 weeks after remobilization (group NS, n=6). At the end of the experimental periods, the soleus muscle was extracted from hindlimb, and the frozen sections were stained with myofibrillar adenosine triphosphatase. After 1 week of remobilization, the means of the muscle fiber diameters for type I fibers in group S had increased significantly compared with group NS, but those for type II fibers in group S did not significantly differ from that for group NS. After 3 weeks of remobilization, the means of the muscle fiber diameters for types I and II fibers in group S had increased significantly compared with group NS. No difference in the fiber type distribution were observed between the experimental group. Our findings suggest that short duration stretching induces recovery from disuse muscle atrophy after joint fixation.

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The breathing movement is highly automated, but it can be voluntarily controlled in some situations. Compared with period of exercise and post-exercise, subjects could control breathing more voluntarily in the post-exercise recovery phase. So, we analyzed relationship between the strategy for controlling the breathing movement pattern and energy efficiency in this phase. Fifteen healthy men (mean age, 22.1 years) were subjected to exercise with a bicycle ergometer at 100 W for 5 minutes, then respiratory pattern was measured four times for 5 minutes after exercise. The measurement items were 1) chest expansion, 2) abdomen expansion, 3) tidal volume, 4) respiration rate, 5) minute ventilation, 6) oxygen intake, and 7) heart rate. The items 1) and 2) were measured by a three-dimensional motion analysis system, and the items 3) through 7) were measured by a respiratory gas analyzer. As for the breathing movement pattern, there were differences among the subjects in terms of the rates of increase in chest expansion and in respiration rate after exercise. The subjects were classified into 4 groups according to these differences. The group, in which respiration rate was increased, showed the marked increase in minute ventilation and oxygen intake, and the rapid recovery of heart rate. The group, in which chest expansion rate was increased, on the other hand, showed small increase in minute ventilation and oxygen intake, and the slow recovery of heart rate. The breathing strategies which are beneficial to energy efficiency exist, however, healthy men do not always select the beneficial strategies.

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Prevention of disuse muscle atrophy is an important problem in physical therapy. Although several reports have been published concerning the effect of weight bearing on the prevention of disuse atrophy of lower extremity muscles, few basic clinical data are available. The present study was undertaken to examine differences in the progression of disuse muscle atrophy in terms of the time when weight bearing is started. The experimental materials consisted of the soleus muscles of 30 male Wistar rats (weight: 220 6 g). The rats were divided into the control group (CON) and the experimental group, and disuse muscle atrophy caused by non-weight bearing was induced by hindlimb suspension for two weeks in the latter group. The experimental group was subdivided into four groups: no weight bearing permitted (SUS), and daily weight bearing permitted from 1, 4 and 7 days after the start of suspension (1-D, 4-D and 7-D). The relative weight of the soleus muscles did not differ for CON and 1-D or for 7-D and SUS. The mean cross-sectional area of type I fibers was 68% of that of CON for 1-D, 61% for 4-D, 52% for 7-D and 52% for SUS. This parameter showed significant differences any two groups, except for between 7-D and SUS. The results were regarded as normal in view of differences in the total time of weight bearing. The data also suggested that disuse muscle atrophy can be prevented quantitatively if weight bearing is initiated from the day following the start of suspension, and that early start of weight bearing is more effective for controlling atrophy progression.

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This study was investigated the influence by ovariectomy (OVX) and calcium diet on bone properties in eighty-one female ICR strain mice with age of 5 weeks. The animals were randomly assigned to sham operation (SHAM), OVX, SHAM+low Ca intake (L.Ca) and OVX+L.Ca group. They were euthanized with lethal dose of pentobarbital sodium at day 50, 100 and 140 post-operatively. For determining the bone properties, both femur and tibial bones were excised from the hind limb, and removed off surrounding tissues. Thereafter, bone length, bone dry weight, and also mechanical strength and ash content of the bones were determined. The bone length on both femur and tibia was significantly longer in OVX group than in the other groups after 50 day of experiment, this situation was continued to the end of the experiment. Bone dry weight, mechanical strength, and ash content were significantly decreased by OVX and L.Ca over the time of the experiment, and those of OVX+L.Ca group were the lowest in all groups. OVX and L.Ca have a great potential for weakening the mechanical strength and have an additive effect when combined. OVX and L.Ca block the gain of bone mass.

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We studied the effect of treadmill exercise on muscle fibers in mice with experimental steroid myopathy. Frozen sections of the extensor digitorum longus (EDL) and soleus (SOL) muscles were stained with hematoxylin-eosin, and the muscle fiber diameters measured. In the EDL, muscle fiber diameters in the steroid groups decreased significantly compared with those in the control groups; moreover, muscle fiber diameters in the exercise groups increased significantly compared with those in the non-exercise groups, whereas the diameters in the SOL did not differ. We speculate that treadmill exercise may prevent corticosteroid-induced muscle fiber atrophy.

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