A study was conducted to investigate the influence of a series of quick stretches during tetanic stimulation of skeletal muscle fibers in growing mice.Mice were anesthetized with pentobarbital sodium. The distal tendon of the extensor digitorum longus muscle was attached to a servomotor. The effects on the muscles of a series of isometric contractions (ISO), a series of quick stretches during contractions (ST), and a sham operation for 1 h were assessed in terms of changes in tetanic tension, serum creatine kinase and lactate dehydrogenase activities, and the histological appearance of the muscle.The data indicated the following ; 1) Serum enzyme activities were not altered in any of the experiments. 2) ST resulted in a decrease in tetanic tension compared with ISO values in mice of all ages. The rate of decrease in tetanic tension for 1 h ST was higher in muscles of young mice than in those of mature mice. 3) Muscle histology demonstrated numerous areas of localized sarcomere widening immediately after the series of ST.These observations suggest that muscle stretching during contraction causes greater injury to developing skeletal muscles.
The mass and structure of bone tissue adapt to the mechanical loads imparted by gravity and movement, and are controlled by the balance between bone formation and bone resorption. The primary adaptations of bone to disuse are demineralization and loss (thinning) of trabecular and cortical bone. Exercise training and electrical muscle stimulation (ES) induce adaptive changes in bone that improve bone strength and inhibit bone loss. ES has been generally applied to patients undergoing physical rehabilitation to maintain and/or recover muscle mass and force-generating capacity in disused muscles. ES-induced muscle contraction of disused muscle can also ameliorate deleterious post-disuse adaptation of bone. The mechanical effects of ES-induced muscle contraction are essential for the maintenance of bone mass and strength, which are achieved through the cooperative functions of osteocytes, osteoblasts, and osteoclasts. The effects of ES, however, are dependent on the stimulation paradigm, including the intensity, frequency, and number of stimuli and the duration of the intervention. This review summarizes the literature on the effects of ES-induced muscle contraction on disuse osteopenia.
The variation of lengths, cross-sectional areas, weights, tetanic tensions, and passive tensions in extensor digitorum longus muscles in mice were investigated during postnatal growth. The increase of tetanic tension was discussed in relation to morphological changes of muscle. The muscle lengths were measured at right angle of articulatio genus and talocruralis (L0) . Following results were obtained: 1) The length, cross-sectional area and weight of muscle increased rapidly up to 7 th weeks, and tetanic tension developed significantly in 2 nd to 5 th week. 2) The muscle length (ML), muscle cross-sectional area (MCA) and muscle weight (MW) correlated significantly with the measured tetanic tension (TT) at L0 (the correlation coefficient r=0.852, 0.886 and 0.903 in ML, MCA and MW respectively) . 3) TT/MCA and TT/MW decreased in 7 th to 8 th week. 4) The passive tension at 130% L0per MCA showed maximum values in 8 th and 9 th weeks. 5) Relative muscle endurance were reduced in 2 nd to 4 th week and reached to steady level after 4 th week. These observations suggest that the functional development of muscle is late for morphological one and/or rapid morphological increment affects the contractile properties of muscle.
The present study was performed to investigate the effect of long distance walking upon physical functions for healthy male subjects. The first experiment was carried out in 1977, the second, in 1978, and the third, in 1979 in each autum season. At the first experiment, subjects began walking upon having breakfast, then ate and drank noting during first 30km, and took some foods during another 26km. Twelve hours and fifty minutes of time was spent for 56km walking including 15, 60, and 30 minutes rest periods in between. In the second experiment, subjects ate nothing after dinner of the previous evening and 35km walking took 6 hours during which some rest periods were taken for blood sampling. The third was 80km walking for two days. Subjects walked 40km in 8 hours in the first day and on the following day they walked 40km in ten hours and twenty minutes. They took foods and rest freely.From the view points of the changes in blood and urinary recordings obtained from those three experiments, the influences of long distance walking on the body indicate as follows ;1) In case of long distance walking while nothing to eat and drink, the rate of serum saturated fatty acids composition decreased and unsaturated fatty acids increased.2) In a fasting state, blood glucose gradually decreased, LDH activity increased and blood lactate, GOT and GPT activity presented no significant changes on long distance walking.3) It was shown that the longer distance to walk, the lesser tendency in blood triglyceride even though subjects take a carbohydrate rich diet while walking.4) In fasting state, less than 35km walking without foods, the stress to the body seemed not to be critical.5) More than 40km walking in a day, even though taking meals, would result a significantly severe stress for body.6) As long as usual meals are taken, 80km walking for two days continuously, 40km in each day, would not result in such a physical stress over the following days.
Markedly smaller myofibers including branched myofibers (SF) were contained in regenerated skeletal muscles. However, its functional properties are not yet sufficiently understood. The present study examined the metabolic, contractile properties and hypertrophy of SF included in rat skeletal plantaris muscles regenerated from eccentric contraction-induced muscle injury. Succinate dehydrogenase and alpha-glycerophosphate dehydrogenase activity of SF were respectively similar to that of other normal size myofibers (NF) within regenerated muscles. The shortening velocity of skinned fibers prepared from branched myofibers isolated from regenerated muscles was slightly slower than that of control muscles. In addition, the extent of glycogen depletion in SF was similar to that of NF after exhaustive running. Therefore, SF were innervated by motoneurons and recruited during the contractile activity of the skeletal muscle. No matter when the regenerated muscle was loaded by synergistic ablation, the continued existence of SF was observed. Therefore, the ability of hypertrophy in SF may be distinct from that in NF. The physiological properties of SF were similar to that of normal myofiber, except for the ability to regulate hypertrophy.
The purpose of the present study was to investigate the influence of training on the metabolism of plasma free fatty acid (FFA), and fatty acid (FA) composition of plasma FFA and adipose tissue triglyceride (TG). The results are summarized as follows: 1) There were no significant differences between pre- and post-training values in the total plasma FFA. 2) Among the individual FFA at rest, the percentage of saturated FA increased and unsaturated FA decreased as a result of physical training. 3) Comparing trained group with untrained group, similar differences were observed in FA composition of plasma FFA and the adipose tissue TG. There were higher percentage of saturated FA and lower percentage of unsaturated FA in the trained group. The above resluts suggested that FA pattern and FA metabolism of plasma and adipose tissue are changed under the influence of physical training.
