Muscle Performance as a Predictor of Bone Health: Among Community-Dwelling Postmenopausal Japanese Women from Setagaya-Aoba Study.

Osteoporosis is a significant health concern for postmenopausal women, necessitating efficient screening methods for bone health. This study explores the potential of muscle function, assessed through the 30-s chair stand test (CS-30), as an indicator for low bone stiffness in this demographic, aiming to establish a practical threshold for large-scale fitness surveillance without the need for specialized tools. We analyzed data from 1055 community-dwelling postmenopausal Japanese women, aged 41-89 years, collected between 2016 and 2019. Participants underwent CS-30 to evaluate muscle function alongside quantitative ultrasound (QUS) measurements to assess bone stiffness. The cohort was divided into two groups for the development and validation of a cutoff point for low bone stiffness, defined as a QUS speed of sound less than 1487.3 m/s. The CS-30 cutoff was determined using receiver operating characteristic (ROC) curve analysis and validated through logistic regression, accounting for age, body mass index, and smoking status. Among 577 postmenopausal women, 16.0% exhibited low bone stiffness. In the development group (n = 382), ROC analysis identified a CS-30 cutoff of 25 repetitions for detecting low bone stiffness, with an area under the curve of 0.744 (P < 0.001). In the validation group (n = 195), participants performing ≥ 25 repetitions had a higher risk of low bone stiffness compared to those performing ≤ 24 repetitions. The CS-30 test is an effective preliminary screening tool for identifying postmenopausal women at risk of low bone stiffness, with a threshold of 25 repetitions. This method could facilitate early detection of individuals at higher osteoporosis risk, promoting timely intervention.

Identification of Genomic Predictors of Muscle Fiber Size.

The greater muscle fiber cross-sectional area (CSA) is associated with greater skeletal muscle mass and strength, whereas muscle fiber atrophy is considered a major feature of sarcopenia. Muscle fiber size is a polygenic trait influenced by both environmental and genetic factors. However, the genetic variants underlying inter-individual differences in muscle fiber size remain largely unknown. The aim of our study was to determine whether 1535 genetic variants previously identified in a genome-wide association study of appendicular lean mass are associated with the CSA of fast-twitch muscle fibers (which better predict muscle strength) in the m. vastus lateralis of 148 physically active individuals (19 power-trained and 28 endurance-trained females, age 28.0 ± 1.1; 28 power-trained and 73 endurance-trained males, age 31.1 ± 0.8). Fifty-seven single-nucleotide polymorphisms (SNPs) were identified as having an association with muscle fiber size (p < 0.05). Of these 57 SNPs, 31 variants were also associated with handgrip strength in the UK Biobank cohort (n = 359,729). Furthermore, using East Asian and East European athletic (n = 731) and non-athletic (n = 515) cohorts, we identified 16 SNPs associated with athlete statuses (sprinter, wrestler, strength, and speed-strength athlete) and weightlifting performance. All SNPs had the same direction of association, i.e., the lean mass-increasing allele was positively associated with the CSA of muscle fibers, handgrip strength, weightlifting performance, and power athlete status. In conclusion, we identified 57 genetic variants associated with both appendicular lean mass and fast-twitch muscle fiber size of m. vastus lateralis that may, in part, contribute to a greater predisposition to power sports.

Coculture with Colon-26 cancer cells decreases the protein synthesis rate and shifts energy metabolism toward glycolysis dominance in C2C12 myotubes.

Cancer cachexia is the result of complex interorgan interactions initiated by cancer cells and changes in patient behavior such as decreased physical activity and energy intake. Therefore, it is crucial to distinguish between the direct and indirect effects of cancer cells on muscle mass regulation and bioenergetics to identify novel therapeutic targets. In this study, we investigated the direct effects of Colon-26 cancer cells on the molecular regulating machinery of muscle mass and its bioenergetics using a coculture system with C2C12 myotubes. Our results demonstrated that coculture with Colon-26 cells induced myotube atrophy and reduced skeletal muscle protein synthesis and its regulating mechanistic target of rapamycin complex 1 signal transduction. However, we did not observe any activating effects on protein degradation pathways including ubiquitin-proteasome and autophagy-lysosome systems. From a bioenergetic perspective, coculture with Colon-26 cells decreased the complex I-driven, but not complex II-driven, mitochondrial ATP production capacity, while increasing glycolytic enzyme activity and glycolytic metabolites, suggesting a shift in energy metabolism toward glycolysis dominance. Gene expression profiling by RNA sequencing showed that the increased activity of glycolytic enzymes was consistent with changes in gene expression. However, the decreased ATP production capacity of mitochondria was not in line with the gene expression. The potential direct interaction between cancer cells and skeletal muscle cells revealed in this study may contribute to a better fundamental understanding of the complex pathophysiology of cancer cachexia.NEW & NOTEWORTHY We explored the potential direct interplay between colon cancer cells (Colon-26) and skeletal muscle cells (C2C12 myotubes) employing a noncontact coculture experimental model. Our findings reveal that coculturing with Colon-26 cells substantially impairs the protein synthesis rate, concurrently instigating a metabolic shift toward glycolytic dominance in C2C12 myotubes. This research unveils critical insights into the intricate cellular cross talk underpinning the complex pathophysiology of cancer cachexia.

Monocarboxylate transporter 4 deficiency enhances high-intensity interval training-induced metabolic adaptations in skeletal muscle.

High-intensity exercise stimulates glycolysis, subsequently leading to elevated lactate production within skeletal muscle. While lactate produced within the muscle is predominantly released into the circulation via the monocarboxylate transporter 4 (MCT4), recent research underscores lactate's function as an intercellular and intertissue signalling molecule. However, its specific intracellular roles within muscle cells remains less defined. In this study, our objective was to elucidate the effects of increased intramuscular lactate accumulation on skeletal muscle adaptation to training. To achieve this, we developed MCT4 knockout mice and confirmed that a lack of MCT4 indeed results in pronounced lactate accumulation in skeletal muscle during high-intensity exercise. A key finding was the significant enhancement in endurance exercise capacity at high intensities when MCT4 deficiency was paired with high-intensity interval training (HIIT). Furthermore, metabolic adaptations supportive of this enhanced exercise capacity were evident with the combination of MCT4 deficiency and HIIT. Specifically, we observed a substantial uptick in the activity of glycolytic enzymes, notably hexokinase, glycogen phosphorylase and pyruvate kinase. The mitochondria also exhibited heightened pyruvate oxidation capabilities, as evidenced by an increase in oxygen consumption when pyruvate served as the substrate. This mitochondrial adaptation was further substantiated by elevated pyruvate dehydrogenase activity, increased activity of isocitrate dehydrogenase - the rate-limiting enzyme in the TCA cycle - and enhanced function of cytochrome c oxidase, pivotal to the electron transport chain. Our findings provide new insights into the physiological consequences of lactate accumulation in skeletal muscle during high-intensity exercises, deepening our grasp of the molecular intricacies underpinning exercise adaptation. KEY POINTS: We pioneered a unique line of monocarboxylate transporter 4 (MCT4) knockout mice specifically tailored to the ICR strain, an optimal background for high-intensity exercise studies. A deficiency in MCT4 exacerbates the accumulation of lactate in skeletal muscle during high-intensity exercise. Pairing MCT4 deficiency with high-intensity interval training (HIIT) results in a synergistic boost in high-intensity exercise capacity, observable both at the organismal level (via a treadmill running test) and at the muscle tissue level (through an ex vivo muscle contractile function test). Coordinating MCT4 deficiency with HIIT enhances both the glycolytic enzyme activities and mitochondrial capacity to oxidize pyruvate.

Belt electrode tetanus muscle stimulation reduces denervation-induced atrophy of rat multiple skeletal muscle groups.

Belt electrode-skeletal muscle electrical stimulation (B-SES) involves the use of belt-shaped electrodes to contract multiple muscle groups simultaneously. Twitch contractions have been demonstrated to protect against denervation-induced muscle atrophy in rats, possibly through mitochondrial biosynthesis. This study examined whether inducing tetanus contractions with B-SES suppresses muscle atrophy and identified the underlying molecular mechanisms. We evaluated the effects of acute (60 Hz, 5 min) and chronic (60 Hz, 5 min, every alternate day for one week) B-SES on the tibialis anterior (TA) and gastrocnemius (GAS) muscles in Sprague-Dawley rats using belt electrodes attached to both ankle joints. After acute stimulation, a significant decrease in the glycogen content was observed in the left and right TA and GAS, suggesting that B-SES causes simultaneous contractions in multiple muscle groups. B-SES enhanced p70S6K phosphorylation, an indicator of the mechanistic target of rapamycin complex 1 activity. During chronic stimulations, rats were divided into control (CONT), denervation-induced atrophy (DEN), and DEN + electrically stimulated with B-SES (DEN + ES) groups. After seven days of treatment, the wet weight (n = 8-11 for each group) and muscle fiber cross-sectional area (CSA, n = 6 for each group) of the TA and GAS muscles were reduced in the DEN and DEN + ES groups compared with that in the CON group. The DEN + ES group showed significantly higher muscle weight and CSA than those in the DEN group. Although RNA-seq and pathway analysis suggested that mitochondrial biogenesis is a critical event in this phenomenon, mitochondrial content showed no difference. In contrast, ribosomal RNA 28S and 18S (n = 6) levels in the DEN + ES group were higher than those in the DEN group, even though RNA-seq showed that the ribosome biogenesis pathway was reduced by electrical stimulation. The mRNA levels of the muscle proteolytic molecules atrogin-1 and MuRF1 were significantly higher in DEN than those in CONT. However, they were more suppressed in DEN + ES than those in DEN. In conclusion, tetanic electrical stimulation of both ankles using belt electrodes effectively reduced denervation-induced atrophy in multiple muscle groups. Furthermore, ribosomal biosynthesis plays a vital role in this phenomenon.

Alterations in neuromuscular junction morphology with ageing and endurance training modulate neuromuscular transmission and myofibre composition.

Both ageing and exercise training affect the neuromuscular junction (NMJ) structure. Morphological alterations in the NMJ have been considered to influence neuromuscular transmission and myofibre properties, but the direct link between the morphology and function has yet to be established. We measured the neuromuscular transmission, myofibre composition and NMJ structure of 5-month-old (young) and 24-month-old untrained (aged control) and trained (aged trained) mice. Aged trained mice were subjected to 2 months of endurance training before the measurement. Neuromuscular transmission was evaluated in vivo as the ratio of ankle plantar flexion torque evoked by the sciatic nerve stimulation to that by direct muscle stimulation. The torque ratio was significantly lower in aged mice than in young and aged trained mice at high-frequency stimulations, showing a significant positive correlation with voluntary grip strength. The degree of pre- to post-synaptic overlap of the NMJ was also significantly lower in aged mice and positively correlated with the torque ratio. We also found that the proportion of fast-twitch fibres in the soleus muscle decreased with age, and that age-related denervation occurred preferentially in fast-twitch fibres. Age-related denervation and a shift in myofibre composition were partially prevented by endurance training. These results suggest that age-related deterioration of the NMJ structure impairs neuromuscular transmission and alters myofibre composition, but these alterations can be prevented by structural amelioration of NMJ with endurance training. Our findings highlight the importance of the NMJ as a major determinant of age-related deterioration of skeletal muscles and the clinical significance of endurance training as a countermeasure. KEY POINTS: The neuromuscular junction (NMJ) plays an essential role in neuromuscular transmission and the maintenance of myofibre properties. We show that neuromuscular transmission is impaired with ageing but recovered by endurance training, which contributes to alterations in voluntary strength. Neuromuscular transmission is associated with the degree of pre- to post-synaptic overlap of the NMJ. Age-related denervation of fast-twitch fibres and a shift in myofibre composition toward a slower phenotype are partially prevented by endurance training. Our study provides substantial evidence that age-related and exercise-induced alterations in neuromuscular transmission and myofibre properties are associated with morphological changes in the NMJ.

Nutritional Value of Yogurt as a Protein Source: Digestibility/Absorbability and Effects on Skeletal Muscle.

Yogurt is a traditional fermented food that is accepted worldwide for its high palatability and various health values. The milk protein contained in yogurt exhibits different physical and biological properties from those of non-fermented milk protein due to the fermentation and manufacturing processes. These differences are suggested to affect the time it takes to digest and absorb milk protein, which in turn will influence the blood levels of amino acids and/or hormones, such as insulin, and thereby, the rate of skeletal muscle protein synthesis via the activation of intracellular signaling, such as the mTORC1 pathway. In addition, based on the relationship between gut microbiota and skeletal muscle conditions, yogurt, including lactic acid bacteria and its metabolites, has been evaluated for its role as a protein source. However, the substantial value of yogurt as a protein source and the additional health benefits on skeletal muscle are not fully understood. The purpose of this review is to summarize the research to date on the digestion and absorption characteristics of yogurt protein, its effect on skeletal muscle, and the contribution of lactic acid bacterial fermentation to these effects.

Dietary apple polyphenols enhance mitochondrial turnover and respiratory chain enzymes.

Previous studies have demonstrated the beneficial effects of apple polyphenol (AP) intake on muscle endurance. Since mitochondria are critical for muscle endurance, we investigated mitochondrial enzyme activity, biogenesis, degradation and protein quality control. Twenty-four Wistar rats were randomly fed a 5% AP diet (5% AP group, n = 8), a 0.5% AP diet (0.5% AP group, n = 8), or a control diet (control group, n = 8). After a 4-week feeding period, the expression level of peroxisome proliferator-activated receptor γ coactivator-1α, a mitochondrial biosynthetic factor, did not increase, whereas that of transcription factor EB, another regulator of mitochondrial synthesis, significantly increased. Moreover, the mitochondrial count did not differ significantly between the groups. In contrast, mitophagy-related protein levels were significantly increased. The enzymatic activities of mitochondrial respiratory chain complexes II, III and IV were significantly higher in the AP intake group than in the control group. We conclude that AP feeding increases the activity of respiratory chain complex enzymes in rat skeletal muscles. Moreover, mitochondrial biosynthesis and degradation may have increased in AP-treated rats. NEW FINDINGS: What is the central question of this study? Does the administration of apple polyphenols (AP) affect mitochondrial respiratory chain complex enzyme activity, biogenesis, degradation and protein quality control in rat skeletal muscles? What is the main finding and its importance? AP feeding increases respiratory chain complex enzyme activity in rat skeletal muscle. Moreover, AP administration increases transcription factor EB activation, and mitophagy may be enhanced to promote degradation of dysfunctional mitochondria, but mitochondrial protein quality control was not affected.

Association of MMP3 gene polymorphism and sex on recovery of muscle strength after eccentric exercise.

Individual differences in recovery of muscle strength after eccentric exercise may be influenced by sex and genotype. A candidate genetic polymorphism associated with response during muscle recovery is the MMP3 gene rs522616 polymorphism, encoding matrix metalloproteinase (MMP-3). Here, we investigated the effect of the MMP3 gene rs522616 polymorphism and sex on recovery of muscle strength after eccentric exercise. A total of 95 healthy subjects (50 men and 45 women) performed five sets of six maximal eccentric elbow flexion exercises. Maximal voluntary contraction (MVC) torque, range of motion (ROM), and muscle soreness, as well as blood parameters [creatine kinase (CK) and interleukin-6 (IL-6)], were assessed immediately before and after and 1, 2, 3, and 5 days after eccentric exercise. No significant time × group interaction in MVC torque after exercise was observed between groups in both sexes. Furthermore, sex differences were identified in the area under the curves (AUC) of CK and IL-6, both of which were higher in men than those in women. A significant genotype-sex interaction was identified in the recovery of MVC, calculated by subtracting the MVC immediately after exercise from the MVC on day 5 after eccentric exercise. The G allele showed a significantly lower recovery of MVC than the AA genotype in men. However, no significant differences were observed in women. This study demonstrated the interaction between the MMP3 rs522616 polymorphism and sex in recovery of muscle strength after eccentric exercise.NEW & NOTEWORTHY Sex differences were identified in the AUC of creatin kinase (CK) and interleukin 6 (IL-6) after eccentric exercise, both of which were greater in men. A genotype-sex interaction was identified in recovery of maximal voluntary contraction (MVC). The G allele showed a significantly lower recovery of MVC than AA genotype in men. To our knowledge, this is the first study to report the interaction between MMP3 gene rs522616 polymorphism and sex difference on recovery of muscle strength after eccentric exercise.

Arterial stiffness and physical fitness on cognitive function in community-dwelling middle-aged and older adults.

PURPOSE: This study examined whether decline in cognitive function is related to arterial stiffness and reduction in physical fitness in middle-aged and older adults. METHODS: A total of 1554 healthy middle-aged and older adults participated in this study. The trail making test parts-A (TMT-A) and B (TMT-B), brachial-ankle pulse wave velocity (baPWV), grip strength, the 30-s chair stand (CS-30) test, the 6-min walk (6MW) test, the 8-foot up-and-go (8UG) test and gait assessment were performed. Participants were classified into a middle-aged group (40-64 years; mean, 50.4 ± 0.2 years) or an older group (≥ 65 years; mean, 73.1 ± 0.5 years), as well as into three cognition (COG) groups (high, moderate, and low) based on median TMT-A and -B scores (high scores on both, either, or neither TMT-A and -B, respectively). RESULTS: The results revealed that baPWV was significantly lower in the high-than in the moderate- and low-COG groups in both middle-aged and older adults (P < 0.05). In addition, except for a few parameters (e.g., 6MW test in middle-aged adults), physical fitness was significantly higher in the high-than in the moderate- and low-COG groups in both middle-aged and older adults (P < 0.05). Multivariate regression analysis revealed that baPWV (P < 0.05) and some physical fitness indicators (grip strength, CS-30, and 8UG) were significantly independently associated with both TMT-A and -B in the middle-aged and older groups (P < 0.05). CONCLUSION: These results suggest that increased arterial stiffness and reduced physical fitness are associated with impaired cognitive function in middle-aged and older adults.

Dietary collagen peptides alleviate exercise-induced muscle soreness in healthy middle-aged males: a randomized double-blinded crossover clinical trial.

BACKGROUND: Post-exercise muscle soreness and fatigue can negatively affect exercise performance. Thus, it is desirable to attenuate muscle soreness and fatigue and promote recovery even for daily exercise habits aimed at maintaining or improving health. METHODS: This study investigated the effects of dietary collagen peptides (CPs) on post-exercise physical condition and fitness in healthy middle-aged adults unfamiliar with exercise. Middle-aged males (n = 20, 52.6 ± 5.8 years) received the active food (10 g of CPs per day) or the placebo food for 33 days in each period of the randomized crossover trial (registered at the University Hospital Medical Information Network Clinical Trials Registry with UMIN-CTR ID of UMIN000041441). On the 29th day, participants performed a maximum of five sets of 40 bodyweight squats. Muscle soreness as the primary outcome, fatigue, the maximum knee extension force during isometric muscle contraction of both legs, the range of motion (ROM), and the blood level of creatine phosphokinase (CPK) and lactate dehydrogenase (LDH) were assessed before and after the exercise load. RESULTS: The analysis set was the per-protocol set (n = 18, 52.6 ± 6.0 years) for efficacy and the full analysis set (n = 19, 52.8 ± 5.9 years) for safety. The visual analog scale (VAS) of muscle soreness immediately after the exercise load was significantly lower in the active group than in the placebo group (32.0 ± 25.0 mm versus 45.8 ± 27.6 mm, p < 0.001). The VAS of fatigue immediately after the exercise load was also significantly lower in the active group than in the placebo group (47.3 ± 25.0 mm versus 59.0 ± 22.3 mm, p < 0.001). Two days (48 hours) afterthe exercise load, muscle strength was significantly higher in the active group than in the placebo group (85.2 ± 27.8 kg versus 80.5 ± 25.3 kg, p = 0.035). The level of CPK did not change over time. The level of LDH increased slightly but was not different between the groups. No safety-related issues were observed. CONCLUSIONS: These results showed that dietary CPs alleviated muscle soreness and fatigue and affected muscle strength after exercise load in healthy middle-aged males.

Hip flexion angle affects longitudinal muscle activity of the rectus femoris in leg extension exercise.

PURPOSE: We investigated the effect of the hip flexion angle (HFA) on the longitudinal muscle activity of the rectus femoris (RF) during leg extension exercise (LEE). METHODS: We conducted an acute study in a specific population. Nine male bodybuilders performed isotonic LEE using a leg extension machine at three different HFAs: 0°, 40°, and 80°. Participants extended their knees from 90° to 0° at each HFA setting for four sets of ten repetitions at 70% of the one-repetition maximum. The transverse relaxation time (T2) of the RF was measured before and after LEE using magnetic resonance imaging. We analyzed the rate of change in the T2 value in the proximal, middle, and distal regions of the RF. The subjective sensation of muscle contraction of the quadriceps was measured using a numerical rating scale (NRS) and compared with the T2 value which was the objective index. RESULTS: At 80°, the T2 value in the middle RF was lower than that in the distal RF (p < 0.05). The T2 values at 0° and 40° HFA were higher than those at 80° HFA in the proximal (p < 0.05, p < 0.01) and middle RF (p < 0.01, p < 0.01). The NRS scores were inconsistent with the objective index. CONCLUSION: These results suggest that the 40° HFA is practical for region-specific strengthening of the proximal RF, and subjective sensation alone as an indication of training may not activate the proximal RF. We conclude that activation of each longitudinal section of the RF is possible depending on the hip joint angle.

Effect of Online Home-Based Resistance Exercise Training on Physical Fitness, Depression, Stress, and Well-Being in Middle-Aged Persons: A Pilot Study.

PURPOSE: This study investigated the effect of online home-based resistance exercise training on fitness, depression, stress, and well-being. A total of 67 individuals participated. Of them, 28 participants (13 men and 15 women, average age: 45.1 ± 12.2 years) performed the same exercise training online (n = 17), using Zoom, or in person (n = 11) in 2020 (Study 1). In addition, 39 participants (15 men and 24 women; average age: 47.6 ± 10.8 years) performed eight weeks of online home-based resistance exercise training in 2021 (Study 2). The participants performed low-load resistance exercises twice a week for eight weeks (16 sessions). Muscle strength, thigh muscle cross-sectional area, fitness parameters, blood pressure, mental health (Center for Epidemiologic Studies-Depression Scale-CES-D; and Kessler Psychological Distress scale-K6), and well-being (Well-Being Index-WHO-5) were measured pre-and post-resistance training. In Study 1, eight weeks of online home-based resistance training improved CES-D (p = 0.003), and a similar tendency was observed in resistance training (RT) with the in-person group (p = 0.06). There was a significant improvement in CES-D symptoms after the online home-based resistance training in Study 2 (p = 0.009). However, there were no significant changes in the WHO-5 and K6. Our results suggest that online low-load resistance training improves fitness parameters and curbs depressive status.

Low-frequency electrical stimulation of bilateral hind legs by belt electrodes is effective for preventing denervation-induced atrophies in multiple skeletal muscle groups in rats.

Belt electrode skeletal muscle electrical stimulation (B-SES) can simultaneously contract multiple muscle groups. Although the beneficial effects of B-SES in clinical situations have been elucidated, its molecular mechanism remains unknown. In this study, we developed a novel rodent B-SES ankle stimulation system to test whether low-frequency stimulation prevents denervation-induced muscle atrophy. Electrical stimulations (7‒8 Hz, 30 min) with ankle belt electrodes were applied to Sprague-Dawley rats daily for one week. All animals were assigned to the control (CONT), denervation-induced atrophy (DEN), and DEN + electrical stimulation (ES) groups. The tibialis anterior (TA) and gastrocnemius (GAS) muscles were used to examine the effect of ES treatment. After seven daily sessions of continuous stimulation, muscle wet weight (n = 8-11), and muscle fiber cross-sectional area (CSA, n = 4-6) of TA and GAS muscles were lower in DEN and DEN + ES than in CON. However, it was significantly higher in DEN than DEN + ES, showing that ES partially prevented muscle atrophy. PGC-1α, COX-IV, and citrate synthase activities (n = 6) were significantly higher in DEN + ES than in DEN. The mRNA levels of muscle proteolytic molecules, Atrogin-1 and Murf1, were significantly higher in DEN than in CONT, while B-SES significantly suppressed their expression (p < 0.05). In conclusion, low-frequency electrical stimulation of the bilateral ankles using belt electrodes (but not the pad electrodes) is effective in preventing denervation-induced atrophy in multiple muscles, which has not been observed with pad electrodes. Maintaining the mitochondrial quantity and enzyme activity by low-frequency electrical stimulation is key to suppressing muscle protein degradation.

Trabecular Bone Volume Is Reduced, With Deteriorated Microstructure, With Aging in a Rat Model of Duchenne Muscular Dystrophy.

We aimed to clarify the effect of aging on trabecular bone volume and trabecular bone microstructure in a rat model of Duchenne muscular dystrophy (DMD). Six rats each of wild type (WT) and DMD model at 15 weeks of age, and 4 rats each at 30 weeks of age, were analyzed by dual energy X-ray absorptiometry and by micro-CT for analysis of trabecular and cortical bone of the femur. Bone mineral density was significantly lower in the DMD group than in the WT group at both 15 and 30 weeks of age. Micro-CT showed that trabecular bone volume and number were not significantly different between the two groups at 15 weeks, but at 30 weeks both were significantly lower in the DMD group than in the WT group. Connectivity density and structure model index were not significantly different between the two groups at 15 weeks, but at 30 weeks they differed significantly. No significant differences between the WT and DMD groups in cortical thickness and cortical area were evident at both 15 and 30 weeks. In conclusion, trabecular bone volume is significantly reduced, with deteriorated microstructure, with aging in a rat model of DMD.

ALDH2 gene polymorphism is associated with fitness in the elderly Japanese population.

PURPOSE: The aldehyde dehydrogenase 2 (ALDH2) rs671 polymorphism, which is exclusive to the Asian population, is related to many diseases. A high reactive oxygen species production in mitochondria, and low muscle strength in athletes and non-athletes, has been observed, as our previous study demonstrated. The purpose of this research was to investigate the influence of ALDH2 rs671 on the loss of muscle strength with aging and replicate our previous study in non-athletes. METHODS: Healthy Japanese individuals (n = 1804) aged 23-94 years were genotyped using DNA extracted from saliva. Muscle strength was assessed using grip strength and chair stand test (CST). The interaction between age and genotypes was analyzed by two-way analysis of covariance (ANCOVA) adjusted for sex, body mass index (BMI), and exercise habit. RESULTS: Individuals aged ≧55 with the AA genotype had a lower performance than those with the GG + GA genotype in the grip strength test (28.1 ± 9.1 kg vs. 29.1 ± 8.3 kg, p = 0.021). There was an interaction between age and genotype, where individuals with ≧55 years old AA genotype had a higher loss of strength compared to GG + GA genotypes in the CST (0.025). No interaction in other models and no sex differences were found. CONCLUSION: This study replicated previous results of the relationship between the AA genotype with lower muscle strength and as a novelty showed that this genotype is associated with a higher age-related loss of strength.

Effects of Competition Level on the Prevalence and Incidence of Lumbar Disk Degeneration in Japanese Collegiate Gymnasts.

Background: Lumbar disk degeneration (LDD) occurs frequently in athletes. Researchers have found that LDD occurs mainly in the lower disks (L4/L5 and L5/S1) in the general and athletic populations. However, a retrospective study showed a high prevalence of LDD in the upper lumbar disks (L1/L2), especially in elite gymnasts. Purpose: To investigate the effect of competition level on the prevalence and incidence of LDD in the upper lumbar disks (L1/L2). Study Design: Cross-sectional study; Level of evidence, 3; and cohort study; Level of evidence, 2. Methods: We conducted 2 studies to evaluate the effect of competition level on the prevalence and incidence of LDD in Japanese collegiate gymnasts. In study 1, a cross-sectional study of 298 collegiate gymnasts was conducted between 2011 and 2015. Competition levels were categorized as regional, national, and international, and T2-weighted magnetic resonance imaging (MRI) was used to evaluate LDD. Chi-square testing was applied to assess differences in the prevalence of LDD and spinal levels among the 3 competition levels. In study 2--a prospective cohort study--LDD progression and its related risk factors were investigated in 51 collegiate gymnasts. Baseline lumbar MRI scans and measurements of physical function (generalized joint laxity and finger-floor distance test) were performed in March 2014. Follow-up lumbar MRI scans were obtained 2 years later, in February 2016. Logistic regression analyses were performed to investigate the relationship between competition level and LDD progression. Results: In study 1, the prevalence of at least 1 degenerated disk in the regional, national, and international groups was 44.2% (19/43), 44.7% (98/219), and 52.8% (19/36), respectively (P = .655). The prevalence of LDD at L1/L2 in the international group was significantly higher than that in the other 2 groups (P = .018). In study 2, the presence of LDD at L1/L2 was associated significantly with international-level competition (adjusted odds ratio, 47.8; 95% CI, 2.75-830.50). Conclusion: In Japanese collegiate gymnasts, competing at the international level was found to be a risk factor for LDD at L1/L2.

The Association between Total Genotype Score and Athletic Performance in Weightlifters.

This study aimed to investigate the relationship between power-oriented genetic polymorphisms and weightlifting status, create a total genotype score (TGS), and validate the association between TGS models and power-oriented athletes. First, 192 weightlifters and 416 controls were studied, and 12 polymorphisms that have previously been associated with strength, power status, and phenotype were genotyped using the TaqMan SNP genotyping assay. We calculated the TGS for the 12 polymorphisms using a PWM (power-oriented whole model) and for 6 of them using a WRM (weightlifting-related model) based on a case-control study. Second, the TGS of the WRM was compared for 177 strength and power athletes and 416 controls. There was no significant difference in the PWM score between weightlifters and the controls. Weightlifters and elite weightlifters had higher WRM scores than the controls. However, the WRM score had no association with weightlifting performance. There was no significant difference in the WRM between power-oriented athletes and the controls. Our study was able to create a TGS model for weightlifters based on case-control results. However, the TGS model could not be applied to other power-oriented athletes.

Genetic profile of sports climbing athletes from three different ethnicities.

This study aimed to investigate the ACTN3 R577X, ACE I/D, CKM rs8111989, and TRHR rs7832552 genotypes in climbers and controls in three ethnicities. The study consisted of 258 climbers (Japanese, n = 100; Polish, n = 128; Russian, n = 30) and 1151 controls (Japanese: n = 332, Polish: n = 635, Russian: n = 184). Genotyping results were analyzed using the TaqMan approach in Japanese and Polish subjects and HumanOmni1-Quad Bead Chips in Russian subjects. There were no significant differences in ACTN3 R577X and ACE I/D polymorphism distribution between climbers and controls in any ethnic cohort or model. The frequencies of the C allele in the CKM polymorphism and the T allele in the TRHR polymorphism were higher in climbers than in controls only in the Russian cohort (p = 0.045 and p = 0.039, respectively). The results of the meta-analysis on three cohorts showed that the frequency of XX + RX genotypes in the ACTN3 R577X polymorphism was significantly higher in climbers than that in the controls (p = 0.01). The X allele of the ACTN3 R577X polymorphism was associated with sport climbing status, as assessed using a meta-analysis of climbers across three different ethnicities.

The Association between the ALDH2 rs671 Polymorphism and Athletic Performance in Japanese Power and Strength Athletes.

The rs671 polymorphism is associated with the enzymatic activity of aldehyde dehydrogenase 2 (ALDH2), which is weakened by the A allele in East Asians. We recently reported the association of this polymorphism with the athletic status in athletic cohorts and the muscle strength of non-athletic cohorts. Therefore, we hypothesized the association of ALDH2 rs671 polymorphism with the performance in power/strength athletes. We aimed to clarify the relationship between the ALDH2 rs671 polymorphism and performance in power/strength athletes. Participants comprising 253 power/strength athletes (167 men and 86 women) and 721 healthy controls (303 men and 418 women) were investigated. The power/strength athletes were divided into classic powerlifting (n = 84) and weightlifting (n = 169). No differences in the genotypes and allele frequencies of the ALDH2 rs671 polymorphism and an association between performance and the ALDH2 rs671 genotype were observed in weightlifters. However, the relative values per body weight of the total record were lower in powerlifters with the GA + AA genotype than those with the GG genotype (7.1 ± 1.2 vs. 7.8 ± 1.0; p = 0.010, partial η2 = 0.08). Our results collectively indicate a role of the ALDH2 rs671 polymorphism in strength performance in powerlifters.