Hypoxic condition of skeletal muscle is caused not only by hypoxia exposure but also by exercise and disease etc. It is thought that clarifying a mechanism of response to hypoxia in vivo is useful for developing better training methods and treatment strategies. However, at present, research dealing with the effects of hypoxic exposure on skeletal muscle have not shown consistent results. Hypoxic exposure results in angiogenesis or muscle atrophy as morphological changes in skeletal muscle. Applications of hypoxic exposure include intermittent hypoxic exposure and hypoxic training, both of which may lead to angiogenesis in a mechanism different from normal hypoxic exposure. In this review, we present some findings on the effects of hypoxia exposure on skeletal muscle and discuss whether satellite cells are involved in promoting angiogenesis by hypoxia.
This study aimed to clarify the relative growth in thigh muscle size and sprint performance in children from 3 to 15 years. A total of 902 children performed a 30-m sprint test. Sprint time was measured by a photocell system. Muscle thicknesses of thigh anterior and posterior were determined by using a B-mode ultrasound. For 431 children, step frequency (SF) and step length (SL) during the sprint running were also analyzed with the films, and corrected by leg length. Using an allometry equation based on body height, relative growth of thigh muscle size and sprint performance was estimated. In both boys and girls, there was a breakpoint (BP) at which the rate of development in sprint velocity changes, and the rate of development was slower after the BP. On the other hand, the rate of growth in thigh muscle size after the BP was superior to that before the point, except of thigh posterior in boys. Regardless of sex, the rate of development in SL index after the BP became to be lower with increasing body height, whereas SF index relatively increased. These current findings indicate that in boys and girls, the rate of development in sprint velocity becomes to be lower above a certain body height, and the relative slow development may result from those in SF and SL.
Arterial stiffness in endurance athletes is low, whereas arterial stiffness in strength athletes is high. The adaptation of the arterial stiffness may be different depending on the training type. On the other hand, there are mixed-trained athletes that can’t be classified as endurance- or strength- trained athletes. The aim of this study was to investigate the arterial stiffness among mixed-trained athletes. The total of 51 young male athletes (15 long-distance runners, 10 handball players and 26 kendo players) and 16 young healthy sedentary individuals (control group) participated in this study. Carotid-femoral pulse wave velocity (cfPWV), carotid-brachial PWV (cbPWV) and femoral-ankle PWV (faPWV), were measured as indices of central and peripheral (upper and lower limbs) arterial stiffness, respectively. cfPWV showed significantly lower in long-distance runners (high endurance capacity) and handball players (strength and high endurance capacities) compared with kendo players (strength and low endurance capacities) and control groups (P < 0.05 for both). cbPWV showed significantly lower in handball players and kendo players compared with the control group (P < 0.05 for both). There was no difference in faPWV among the groups. These data suggest that the competitive characteristics of athletes (i.e., endurance capacity or target muscle groups of sport) influence the adaptation of arterial stiffness. It can be speculated that endurance capacity in mixed-trained athletes can affect central arterial stiffness and similar to endurance trained athletes. In addition, the adaptation in upper limb arterial stiffness will be included in the training effects associated with the sports-specific target muscle groups, while lower limb arterial stiffness may not be unaffected by any type of exercise.
The purpose of this study was to consider the validity of measuring the Star Excursion Balance Test (SEBT), which has been used as a measure of balance ability in athletes, for community-dwelling elderly people. To achieve this purpose, we examined the relationship between the existing balance ability measures, leg strength, and the SEBT. The subjects were 36 elderly people (mean age: 71.1 years). We used the SEBT, functional reach test (FRT), timed up-and-go test (TUG), and Mini-BESTest to evaluate balance ability and the 30-second chair-stand test (CS-30) to assess leg strength; we also assessed the 10-m walk time. The correlation coefficient with the SEBT was calculated. The significant level was 5%. A significant positive correlation was observed between the total score of Mini-BESTest and the SEBT reach distance in the anterior direction (r = 0.364, p < 0.05) and the posteromedial direction (r = 0.407, p < 0.05). A significant positive correlation was observed between anticipatory postural control and the SEBT reach distance in the anterior directions (r = 0.403, p < 0.05), and postural responses and SEBT reach distance in the posterolateral direction (r = 0.360, p < 0.05), which were subsystem category of Mini-BESTest. No significant correlation was found in the other items. The correlation with Mini-BESTest indicates that SEBT might be a valid tool to evaluate the dynamic balance ability of community-dwelling elderly people. However, their correlation coefficient is not high, suggesting that SEBT can evaluate elements different from Mini-BESTest.
This study examined variations in shoulder loading due to differences in the site of stepping foot contact during baseball pitching, while comparing flat ground and mound conditions. Measurement was performed, involving 10 right-handed pitchers who belonged to university baseball clubs, under original flat ground and mound conditions. Pitching movements were classified into 3 categories: [normal], [narrow], and [outside]. Through 3-dimensional motion analysis using a motion capture system, the following results were obtained: 1. The pitching velocity was significantly higher in the [normal] compared with [narrow] and [outside] conditions and under the mound compared with flat ground condition. 2. The peak torque of the shoulder internal rotation was markedly lower in the [narrow] compared with [normal] condition. There were no significant differences between the [normal] and [outside] conditions or between the flat ground and mound conditions. 3. The posterior, superior, and inferior shearing forces, as well as the proximal traction force, which influence the humeral head of the shoulder, were markedly greater in the [normal] compared with [narrow] and [outside] conditions. The anterior and posterior shearing forces and proximal traction force were significantly greater under the mound compared with flat ground conditions. Based on the results, the internal rotation torque of the shoulder, as well as the shearing and traction forces influencing the humeral head of the shoulder, may vary due to differences in the site of stepping foot contact during baseball pitching and between flat ground and mound conditions. The former may also be useful to prevent pitching-related shoulder injuries.
In athletes, repeated intensive exercise is considered to depress the immune system. The purpose of this study was to investigate the effects of yogurt fermented with Lactococcus lactis subsp. cremoris FC (L. cremoris FC) on salivary secretory immunoglobulin A (SIgA) in long-distance runners (high school students) during a 5 day intensive training program. Fourteen subjects were divided into 2 groups: a yogurt fermented with L. cremoris FC intake group and a milk intake group (control group). Each subject consumed yogurt or milk for 5 days during the intensive training. Salivary samples were obtained on days 1 and 5, and SIgA secretion and cortisol levels were measured. In addition, the mood of each subject was evaluated using the Profile of Mood States (POMS) questionnaire. Our study suggested that L. cremoris FC intake increases SIgA secretion. In addition, there might be a significant suppression in the increase of salivary cortisol levels caused by exercise mainly, but there was no effect on mood. These results suggest that L. cremoris FC intake may have health benefits by enhancing oral immune function mediated by SIgA.