The plasticity of skeletal muscle facilitates adaptation to various stimuli. Sex steroid hormones (androgens and estrogens) are involved in a variety of physiological and pathological processes. In skeletal muscle, sex steroid hormones affect growth, strength, metabolism, and antioxidant levels and are associated with exercise-induced skeletal muscular adaptation. Sex steroid hormone levels also decrease with aging and are thought to be a factor in muscle atrophy. Though sex steroid hormones play an important role in skeletal muscular homeostasis, the role of the endocrine system in muscle plasticity is unknown. Sex steroid hormones are synthesized from cholesterol by steroidogenic enzymes, such as 3β-hydroxysteroid dehydrogenase (HSD), and 17β-HSD, with testosterone being irreversibly converted to estrogen by aromatase cytochrome P450 (P450arom). Testosterone is also converted into its bioactive metabolite dihydrotestosterone (DHT) by 5α-reductase. Sex steroid hormones are produced by various peripheral target tissues including the kidney, liver, and brain in addition to endocrine organs such as the testis or ovary in the recent research. For instance, steroidogenic enzymes expressed in skeletal muscle have been reported to locally synthesize sex steroid hormones from circulating dehydroepiandrosterone (DHEA) or testosterone in response to exercise. Thus, local steroidogenesis in skeletal muscle provides further evidence for the presence of an autocrine/paracrine system for sex steroid hormones and their roles in skeletal muscle function and adaptation. This review focuses on the steroidogenesis of skeletal muscle and discusses the physiological significance of the sex steroid hormones network of circulation and skeletal muscle.

The purpose of this study was to evaluate the function of cardiac autonomic nervous activity and post-exercise vagal reaction during the menstrual cycle. The subjects were healthy young women (n=13, age 19.9±0.6 years) with normal menstrual cycles. Power spectral analysis of heart rate variability was used to examine cardiac autonomic nervous activity. In addition, the time con stant of heart rate decline for the first 30 sec (T₃₀) after exercise was used to examine post-exercise vagal reactivation.
Results show that the cardiac autonomic nervous activity changes during the menstrual cycle. Also, T₃₀ shows significant change during the menstrual cycle, especially T₃₀ retardation in the early luteal phase. These results suggest that an imbalance of estradiol and progesterone hormones may be responsible for these changes in cardiac autonomic nervous activity during the menstrual cycle.

‹Objective› In previous animal studies, it has been observed that ovarian hormones centrally alter baroreflex modulation of cardiovagal nervous control. If this central action of ovarian hormones is observed in human females, non-baroreflex modulation of cardiovagal nervous control should change with the menstrual cycle. The hypothesis in this study was that cardiovagal nervous response to facial cold stimuli (non-baroreflex modulation) changes throughout menstrual cycle.‹Subjects and methods› Eight young healthy women with a normal menstrual cycle participated in this study. The menstrual cycle was divided into 5 phases (menstrual, follicular, ovulatory, early luteal and late luteal) . Resing ECG RR intervals, cardiovagal nervous activity (by heart rate variability), RR intervals and cardiovagal nervous response to facial cold stimuli were measured during each menstrual phase. RR intervals and cardiovagal nervous response to facial cold stimuli were evaluated paying attention to the “quantity” and “quickness” of the changes.‹Results› There were no phase differences in resting RR intervals and cardiovagal nervous activity. Quantity of RR intervals and cardiovagal nervous response and quickness of. RR intervals to facial cold stimuli did not change throughout the menstrual cycle. The speed of cardiovagal nervous response to facial cold accelerated in the follicular phase, and to the contrary, slowed down in the early luteal phase, ‹Conclusion› These data suggest the speed of cardiovagal nervous response mediated non-baroreflex mechanism changes throughout the menstrual cycle.

The purpose of this study was to evaluate the change in dynamic and static balance ability during the menstrual cycle among young women. The subjects were young healthy women (n=12, age 20.4±1.2 years) with regular exercise and a normal menstrual cycle. The menstrual cycle was divided into 5 phases : Menstrual, Follicular, Ovulatory, Early luteal and Late luteal. Measurements were taken using the dynamic balance test, static balance test and looseness test. The dynamic balance test did not change during the menstrual cycle. Length Time within the static balance test increased in the late luteal phase compared to other menstrual cycle phases. The deviation of the mean of X within the static balance test increased in the follicular and late luteal phase and decreased in the ovulatory phase. Also, the deviation of the mean of X increased in the follicular phase compared to the menstrual phase and decreased in the menstrual and early luteal phases compared to the follicular and ovulatory. Left arm upper of laxity in hand on the back test within looseness test increased in the menstrual and early luteal phases compared to other menstrual cycle phases. These results suggest that static balance ability changes during the menstrual cycle.

[Objective] This study examined the effects of resting metabolic rate (RMR), sleeping metabolic rate (SMR), and diet-induced thermogenesis (DIT) during acute weight loss in elite male wrestlers.[Methods] Subjects were elite male wrestlers (n=6), who were instructed to reduce the body weight in seven days. RMR, SMR, and DIT were measured by indirect calorimetry in normal training phase and after rapid weight loss. Body composition and energy intake were also measured.[Results] Energy intake significantly decreased in rapid weight loss phase (P<0.05). After the rapid weight reduction, percent reduction of body weight (-4.4%), fat mass (-17.5%), and total body water (-3.2%) significant compare with that of normal training phase (P<0.05). RMR(-15.2%), and SMR (-11.8%) significantly decreased during acute weight loss (P<0.05). DIT(-89.4%) tended to be decrease during acute weight loss.[Conclusion] The present study suggests that rapid weight loss in elite male wrestlers causes decreases in RMR and SMR.

[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.

[Objective] The aim of this investigation was to evaluate salivary dehydroepiandrosterone (DHEA) responses during a competitive period among female football players.
[Methods] Subjects were college female football players (n=9) . Saliva and blood samples were collected at 18 : 00 (6 : 00 pm) and the profile of mood state (POMS) was recorded during a period of normal training (Pre), 3 days of competition (Competition), and a recovery period (Post) . Levels of salivary DHEA, cortisol, and serum creatin kinase (CK), urea nitorogen (UN), were determined.
[Results] The levels of salivary DHEA significantly increased during competition (2 nd days) compared with Pre (p<0.05), and significantly decreased after competition compared with Pre (p<0.05) . The levels of salivary cortisol significantly increased during the competition (2 nd and 3 rd days) compared with Pre (p<0.05) . Whereas it decreased after competition compared with Pre. The levels of serum CK significantly increased during the competition (2 nd days) compared with Pre (p<0.05) . The levels of serum UN did not change during the study. The fatigue score of POMS significantly increased during competition (2 nd days) compared with Pre (p<0.05) .
[Conclusion] These data suggest that DHEA could be a useful endocrinological indicator for evaluating training status in female athletes.

[Objective] The aim of this investigation was to evaluate bone metabolism responses to acute resistance exercise during the menstrual cycle. [Methods] Subjects were young healthy sedentary women (n=7) with regular menstrual cycles. The subjects performed acute resistance exercise in each phase (follicular and luteal) of the menstrual cycle. Bone metabolism markers (bone formation marker BAP and bone resorption marker ICTP), bone metabolism related hormones (parathyroid hormone, calcitonin, calcium and inorganic phosphorus) and lactate were determined. Blood samples were collected before (Pre) and immediately following the exercise (Post), 1 hour (P1h) and 24 hours (P24h) after the exercise. [Results] BAP significantly increased at Post compared with Pre both in the follicular and luteal phases (p<0.05), but significantly decreased at P1h and P24h in the luteal phase. ICTP significantly increased at Post in the follicular phase (p<0.05) and significantly decreased at P1h and P24h in the luteal phase. The bone metabolism responses in the luteal phase moved to low-bone turnover at P1h and P24h. [Conclusion] The bone metabolism response to acute resistance exercise was different between menstrual phases. These results suggest that bone metabolism is influenced by the menstrual cycle.

【Objective】The purpose of this study was to investigate the acute responses of adiponectin and leptin to resistance exercise in healthy elderly men. 【Methods】Eight healthy men (age, 25.5±3.3 yrs) participated in this study. They performed two trials. Trial 1 was an exercise session consisting of 5 resistance exercises at high-intensity (75% one-repetition maximum : 1 RM) with three sets of 10 repetitions. Trial 2 was a control trial at rest for the same time as trial 1. Blood samples were taken to assess adiponectin, leptin, and metabolism related substances (glucose and lipids).【Results】Leptin significantly decreased 24 h after the resistance exercise but did not change in trial 2. Blood insulin and lactate concentrations significantly increased immediately (0 min) and 30 min after the exercise. However, adiponectin, glucose and lipids were not affected. 【Conclusion】Adiponectin was not affected by resistance exercise, whereas leptin decreased 24 h after the exercise. This suggests that leptin may have quite a delayed response to high-intensity resistance exercise.