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.
A motor program for controlling one’s own movement requires sensory signals from the target body parts. Information for movement is provided by sensory feedback such as visual and somatosensory information. Previous studies indicated that cortical activity related to sensory response and perception is modified by movement executing mechanisms. The integration of sensory information and motor command is critical for motor control and recognition of one movement. However, this raises the issue of how central nervous system integrates motor command and sensory information whenever the intended movement is in progress. Preceding and during voluntary movement, the efference copy in relation to motor signal from motor related areas modified the information processing in somatosensory areas. This review introduces the research topics of sensorimotor integration and new findings according to recent studies of the somatosensory system in relation to sports science.
Recently, the China Adult Physical Activity Guideline (CAPAG) have been published. However, it is unclear to know the prevalence of people meeting the CAPAG, and who meet. Therefore, we conducted this study to investigate the prevalence and demographic characteristics of people achieving the recommended CAPAG. Cross-sectional data in the present study was analyzed for 1,655 Chinese urban adults. The Chinese version of International Physical Activity Questionnaire was used to examine CAPAG level of adults. According to CAPAG, Chinese adults are recommend to meet ≥6000 Step/day. Demographic data, including age, marital status, educational level, income level, body mass index and self-rated health were obtained with the questionnaire. To examine the association of demographic and health status with PA level, a multivariate logistic regression analysis was utilized. Overall, 61.1% of respondents met the PA recommendation. Unmarried and healthy (self-rated health) were significantly associated with meeting the physical activity recommendation. Women aged 30 to 39 years were less likely to achieve the recommendation. Women with incomes of 1,000 Yuan or less were more likely to meet the recommendation than those with incomes of 4,000 Yuan or more. Adults with normal weight were more likely to those with underweight. Differences in associations of demographic correlates with the PA recommendation were observed between men and women, which suggest that gender-specific strategies might be more effective in promoting PA among Chinese urban adults.
The aim of this study was to demonstrate a time-series relationship in drop jump (DJ) from a pre-set state with improved performance. Twelve male college athletes performed a DJ from a height of 0.60 m. DJ performance was assessed with a DJ-index (jump height/contact time). Short-interval intracortical inhibition (SICI) was assessed as intracortical inhibitory circuit excitability in a pre-set state, calculated by using paired-pulse transcranial magnetic stimulation for the medial gastrocnemius muscle (MG). The H-reflex of the left MG and the ankle joint torque were calculated in the early phase of take-off. A significant correlation was shown between ⊿SICI during the pre-set state and the DJ index. Thus, we examined the relationships between phases, focusing on time-series relationships throughout the jump period. The results showed a significant correlation between ⊿SICI during the pre-set state and %H-reflex during the early phase of take-off, and peak ankle joint torque during take-off was also significantly correlated with %H-reflex during the early phase of take-off. A significant correlation was also demonstrated between ankle joint torque during take-off and the DJ-index. In conclusion, we observed a time-series relationship between DJ from a pre-set state and improved performance. A decrease of intracortical inhibitory circuit excitability in the pre-set state affects stretch-reflex facilitation during the early phase of take-off; stretch-reflex facilitation results in the development of a large force in the ankle joint during take-off, and this force develops ankle joint torque. These findings may be used to improve jump performance.
The purpose of this study was to examine the association of muscle mass and muscle strength with mobility limitation and history of falls in community-dwelling older adults. This cross-sectional study included 420 older adults (207 men, 213 women, 73.7 ± 5.2 years). The participants were classified to following four groups according to their appendicular skeletal muscle mass index (AMI) which was evaluated by bioelectric impedance analysis for skeletal muscle mass in the arms and legs and appendicular skeletal muscle strength Z-score (ASZ) which was calculated from hand-grip strength for upper extremity and peak reaction force during sit-to-stand movement for lower extremity: 1) Low AMI and Low ASZ, 2) Low AMI alone, 3) Low ASZ alone, and 4) Normal. Mobility limitation and history of falls were assessed as a self-reported questionnaire. We used a poisson regression analysis with an adjustment for age, body mass index, knee pain, and back pain. The prevalence of mobility limitation was significantly higher at Low AMI and Low ASZ (relative risk, RR = 5.09, 95% confidence interval, CI 2.08–12.46) and Low ASZ alone (RR = 4.79, 95% CI 2.01–11.39) in men and Low AMI and Low ASZ (RR = 1.70, 95% CI 1.01–2.88) in women than Normal. History of falls was significantly associated with Low ASZ alone (RR = 2.00, 95% CI 1.02–3.91) just in men. These results suggest that low muscle strength per weight rather than low muscle mass per height is an important risk factor to increase mobility limitation in both genders and falls in men.