This study compared the physical fitness level and weight status of children and adolescents in China and Japan. Children and adolescents aged 7–18 years were recruited (China: n = 5660; Japan: n = 5660). Physical fitness was assessed using seven core items—grip strength, 30-s sit-ups, standing long jump, sit-and-reach, 20-s repeated straddling, 20-m shuttle run test, and 50-m dash. A physical fitness index (PFI) was calculated by adding all items’ Z-scores. We conducted comparisons of PFI and its distribution, each physical fitness item, and weight status for individuals from China and Japan across all ages. The PFI was lower in China than in Japan for all age groups, with an especially large difference at age 18 years for boys (a difference of 9.05) and girls (a difference of 9.10) (p < 0.001). The same result was seen for the seven items. The PFI distribution for children and adolescents was more disperse among those in Japan than among those in China. Obesity prevalence was 2.84 times higher in China than in Japan. An inverted U-shaped relationship was observed between physical fitness and nutritional status. Children and adolescents showed markedly lower physical fitness and higher obesity prevalence in China than in Japan.

Background: In the present study, we examined spinal glial cell activation as a central nervous system mechanism of widespread mechanical hyperalgesia in rats that experienced chronic post-cast pain (CPCP) 2 weeks after cast immobilization. Activated spinal microglia and astrocytes were investigated immunohistologically in lumbar and coccygeal spinal cord segments 1 day, 5 weeks, and 13 weeks following cast removal. Results: In the lumbar cord, astrocytes were activated after microglia. Astrocytes also were activated after microglia in the coccygeal cord, but with a delay that was longer than that observed in the lumbar cord. This activation pattern paralleled the observation that mechanical hyperalgesia occurred in the hindleg or the hindpaw before the tail. The activating transcription factor 3 (ATF3) immune response in dorsal root ganglia (DRG) on the last day of cast immobilization suggested that nerve damage might not occur in CPCP rats. The neural activation assessed by the phosphorylated extracellular signal-regulated kinase (pERK) immune response in DRG arose 1 day after cast removal. In addition, L-α-aminoadipate (L-α-AA), an inhibitor of astrocyte activation administered intrathecally 5 weeks after cast removal, inhibited mechanical hyperalgesia in several body parts including the lower leg skin and muscles bilaterally, hindpaws, and tail. Conclusions: These findings suggest that activation of lumbar cord astrocytes is an important factor in widespread mechanical hyperalgesia in CPCP.

Exercise is an effective intervention to promote bone mass by regulating bone homeostasis, but the specific mechanism is ambiguous. Here this study shows that high-intensity interval training (HIIT) was more effective than low-intensity continuous training (LICT) in promoting bone mineral density (BMD). Lactate, a major by-product of HIIT, emerges as a focal point in our investigation of bone homeostasis regulation. In vitro experiments revealed that lactate promotes osteoblast differentiation while inhibiting osteoclast differentiation. However, this effect is markedly suppressed in Gpr81-deficient osteoblasts and osteoclasts. We next found lactate inhibits osteoclast differentiation via the activation of the Gpr81-TAK1-p65 signaling pathway, while promoting osteoblast differentiation through activation of the Gpr81-Wnt/β-catenin pathway. Subsequently, HIIT interventions were performed using ovariectomized (OVX) mice with osteoporosis. It was found that HIIT not only attenuated bone resorption but also promoted bone formation, thereby partially rescuing the low bone mass phenotype of OVX mice. Furthermore, administering lactate in a mouse model of osteoporosis induced by ovariectomy effectively prevented bone loss. Our results provided a potential drug target for osteoporosis treatment, the activation of Gpr81 holds promise as a potential strategy for preventing osteoporosis.

Background: This study aimed to compare the difference in cardiorespiratory fitness between Chinese and Japanese children and adolescents. Methods: Participants comprised 9025 children and adolescents aged 7–18 years from China and Japan. Cardiorespiratory fitness (CRF) was measured by performance in the 20 m shuttle run test (20mSRT) and estimated maximal oxygen consumption (VO_2max). Differences in CRF between countries were evaluated by t-tests. Centile curves for the 20mSRT and VO_2max values were constructed for Chinese and Japanese children and adolescents, respectively, using the Lambda Mu and Sigma (LMS) method. Results: (1) For most of the age groups, the 20mSRT and VO_2max performances among Chinese participants were lower than among Japanese participants. (2) Japanese children had the most apparent gains in P₁₀, P₅₀, and P₉₀ VO_2max values in primary school; however, they gradually decreased in middle school. For Chinese girls, the P₁₀, P₅₀, and P₉₀ VO_2max values decreased gradually with age. (3) The VO_2max value among Japanese children increased; however, it decreased or remained flat among Chinese children in primary school. Conclusions: CRF among Chinese participants was lower than among Japanese participants while the VO_2max value showed different trends in primary school. Effective measures should be taken to improve CRF among children and adolescents.

The primary aim of this study was to establish sex and age-specific muscular fitness (MF) norms for Chinese children and adolescents aged 7–18 years old. The secondary aim was to compare their MF values with those of children and adolescents in other countries and regions. The MF of 93,755 participants from China was evaluated by handgrip strength (upper limbs strength), sit-ups (trunk strength) and a standing broad jump (lower limbs strength), with a total of 90,424, 90,281 and 90,663 data values, respectively. The Lambda-Mu-Sigma (LMS) method was used to calculate smooth curves and table data. The MF of Chinese boys was higher than that of girls in all age groups. After the age of 11, the growth rate of boys accelerated while that of girls slowed down. Age-related changes were larger for boys than for girls. In the international comparison, all the MF indicators of Chinese children and adolescents were lower than those of their Japanese peers but were higher than those of their European peers, with the exception of handgrip strength. The results of this study can be used to evaluate, monitor and apply interventions that improve MF. They can also be used to compare trends across countries and regions.

Previous studies have noted the associations of sedentary behavior and physical activity with several musculoskeletal disorders (MSDs), yet the causality of these relationships remains unclear. In this study, we probed into the causal associations between sedentary behavior, physical activity, and the risk of 13 MSDs through Mendelian randomization (MR) analysis. We obtained summary statistics for leisure screen time (LST) and moderate-to-vigorous intensity physical activity (MVPA) from genome-wide association studies (GWAS) for 2-sample univariable MR analysis. The linkage disequilibrium score regression (LDSC) was used for genetic correlation analysis. Multivariable MR analysis was conducted on LST and MVPA to adjust for one another. Furthermore, we performed mediation analysis to reveal the potential mediating effect of body mass index (BMI). After Benjamini–Hochberg correction, LST was significantly associated with an increased risk of 8 MSDs, including spinal stenosis, spondylolisthesis, low back pain, cervicobrachial syndrome, rotator cuff syndrome, meniscus derangement, lateral epicondylitis, and gout. All these MSDs had positive genetic correlations with LST. There was no causal effect of MVPA on MSDs. However, after adjusting for LST, the association between MVPA and scoliosis became significant; the associations between LST and all 8 MSDs remained after adjusting for MVPA. Two-step mediation analysis found that BMI mediated all the associations between LST and MSDs. Our study provides genetic evidence supporting that sedentary behavior is a causal risk factor for most MSDs independent of physical activity. These findings offer valuable insights for the development of evidence-based prevention strategies and interventions targeting MSDs.