The discovery of microRNAs (miRNAs) and following studies reporting that miRNAs are stably present in the circulation, paved the way for possible use of miRNAs as biomarkers. Identification of circulating miRNAs that are functional upon delivery to the recipient cells, suggests miRNAs play roles in cell-to-cell communication as well as hormones and cytokines. This review provides a basic understanding of miRNAs and the current understanding of circulating miRNA as biomarkers and focuses on their putative roles and regulation under stressed conditions including physical exercise.

Mitochondria play a central role in energy production but also are the main cellular source of reactive oxygen species (ROS). It is widely believed that aging is related to the accumulation of oxidative molecular damage due to ROS. Aging also induces a decrease in muscle function. Recent studies indicate that caloric restriction and physical exercise suppress the decrease in muscle function though the maintaining quality of mitochondria. This review provides the current understanding of the influence of caloric restriction and exercise on mitochondrial quality control in skeletal muscle.

Skeletal muscle is the dominant organ in locomotion and energy metabolism so that maintaining skeletal muscle function is a prerequisite for our health and independent living throughout the life. A loss or decrease in skeletal muscle function leads to increased morbidity and mortality through the development of secondary diseases such as metabolic syndrome, type 2 diabetes, obesity, cardiovascular and respiratory disease. Identifying mechanisms which influence the processes regulating skeletal muscle function is a key priority. The recent discovery of microRNAs (miRNAs) provides a new knowledge controlling skeletal muscle function. miRNAs suppress gene expression through either in inhibition of protein translation or in degradation of the mRNA transcripts through a process similar to RNA interference (RNAi). This review provides the current understanding in skeletal muscle miRNA biology and focuses on their role and regulation under physiological conditions with exercise.

[Objective] The purpose of this study was to determine whether icing treatment has an effect on muscle reaction time and functional performance of a sprained ankle. [Methods] Subjects were six persons (healthy group) and six persons who had an acute ankle sprain (patient group) . Anterior talar translation and talar tilt of the six patient group were evaluated by the stress X-ray measure. Ice treatment was applied for 20 minutes. [Results] The following points were clarified : 1) Reaction times of peroneus longus (PL) and peroneus brevis (PB) for the sprained ankle group (SA) were significantly longer than those for the non-sprained ankle group (NA) (p<0.05) . Length of time of standing on one leg with closed eyes for SA was significantly shorter than for NA (p<0.05) . 2) After icing treatment, reaction time of PL for SA tended to be shorter. Furthermore, PB significantly decreased after icing treatment (p<0.05) . Side-steps for SA were significantly increased after icing treatment (p<0.05) . 3) Reaction times of PL and PB for NA significantly increased after icing treatment (p<0.05) . Standing on one leg with closed eyes for NA significantly decreased after icing treatment (p<0.05) . [Conclusion] It was shown that icing treatment of a sprained ankle leads to a shorter muscle reaction time and an increase in the number of side-steps. Therefore, it was concluded that icing treatment of a sprained ankle might be able to improve incapacitated neuromuscular function and functional performance by acute trauma.

Infection is the major cause of health impairment in elderly persons. Immune function declines with age. In order to keep the elderly in good health, it is necessary to control the age-associated decline of their immune function. Components of a non-specific immune system arc neutrophils, macrophages and NK cells. A specific immune system is composed of T lymphocytes and B lymphocytes. T lymphocytes differentiate in the thymus. Age-associated atrophy of the thymus causes a decline in T lymphocyte function. It is essential in aging of the immune system. B lymphocytes produce immunoglobulin to act as antibodies. With aging, abnormal antibodies such as autoantibodies and monoclonal immunoglobulin increase, and the number of normal antibodies compared to foreign antigens decrease. Exercise influences the autonomic nervous system, hypothalamo-hypophyseal system, and immune system. Moderate exercise enhances immune function, and severe exercise causes immune function decline. Immune function declines after a severe single bout of exercise, and an “open window” of infections occurs. Appropriate exercise training may improve immune function. Recently, it was shown that exercise training for one year increased the contents of secretory immunoglobulin A in saliva in elderly persons. This result suggests that long-term exercise training improves immune function in elderly persons.

The purpose of this study was to investigate differences between underwater and land-based exercise in leg muscle activity. Nine healthy males (mean age : 21.7±0.5 years, mean height : 173.4±2.2 cm) had electrodes placed on their left leg muscles (Tibialis Anterior ; TA, Medial Gastrocnemius ; MG, Soleus ; SOL, Rectus Femoris ; RF, and Biceps Femoris ; BF), and their muscle activity was measured during various exercises. The subjects performed six types of exercise such as the forward walk, backward walk, squat, calf raise, leg range, and one leg wave, both in the water (waist level) and on land. These exercises were categorized as 3 types of leg movement according to direction ; horizontal, vertical, and mixed movement.
In the forward walk and backward walk, categorized as horizontal movements, the integrated electromyogram (IEMG) significantly increased during underwater exercise compared with on land. In the squat, as a vertical movement, the IEMG showed a similar change under both conditions. In the calf raise, as a vertical movement, and leg range and one leg wave, as mixed movements, the IEMG significantly decreased during underwater exercise compared with on land. These results suggest that leg muscle activity during underwater exercise is different based on the movement direction of the legs. In a word, it was apparent that movement in a horizontal direction underwater provides greater activity for leg muscles than on land; but movement in a vertical and/or mixed direction underwater provides less activity for leg muscles than on land. In prescribing an exercise program, it may be helpful to understand the differences between underwater and land-based exercise in leg muscle activity.

To investigate the effect of intense exercise on immunological factors in saliva, we measured secretory immunoglobulin A (sIgA), lactoferrin and fibronectin. We used a reliable saliva collection method that has already been reported. Timed saliva samples were obtained from 16 healthy young males. Samples were collected before, immediately after, 1 day after and 5 days after endurance running (42.195 km) . The concentrations (μg/ml) of sIgA, lactoferrin and fibronectin were measured by ELISA, and the secretion rates (μg/min) of each were calculated. Immediately after the exercise, the concentration of total protein in saliva increased significantly, but the sIgA secretion rate decreased to 53%. The secretion rates of both lactoferrin and fibronectin did not change significantly. The local immune system plays an important role in mucosal surface defense against upper respiratory tract infection. The sIgA level in the oral cavity was temporarily decreased after intense exercise. A decreased sIgA secretion rate might partly explain the increased susceptibility to upper respiratory tract infection after endurance exercise.

[Objective] The aim of this investigation was to evaluate serum steroid hormone responses to acute resistance exercise. [Methods] Subjects were young healthy males (n=6) and females (n=6) . Each group performed three sets of 10 leg press and 10 bench press exercises at an intensity of their individual 10-repetition maximum (1ORM), with 1 min rest between sets. Blood samples were collected before (Pre-Ex) and immediately following the exercise (P0), 30 mm (P30), 60 mm (P60), and 24 hours (P24h) after the exercise. Levels of blood lactate, serum testosterone, dehydroepian drosterone sulfate (DHEAS) and cortisol were determined. [Results] The levels of blood lactate in males and females significantly increased at P0 and P30 compared with Pre-Ex (p<0.05) . In males, the serum level of testosterone significantly increased at PO (p<0.05), whereas in females, it significantly decreased at P0, P30, P60, P 24 h. (p<0.05) . The level of DHEAS significantly increased at P0 in both males and females (p<0.05) . [Conclusion] The change in the level of testosterone was different between males and females, but that of DHEAS showed a similar pattern for both sexes. The data suggest that DHEAS could be a useful indicator for evaluating the anabolic status of acute resistance exercise in females.