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The relationship between mechanistic target of rapamycin complex 1 (mTORC1) activation after resistance exercise and acetylcholine receptor (AChR) subunit gene expression remains largely unknown. Therefore, we aimed to investigate the effect of electrical stimulation‐induced intense muscle contraction, which mimics acute resistance exercise, on the mRNA expression of AChR genes and the signalling pathways involved in neuromuscular junction (NMJ) maintenance, such as mTORC1 and muscle‐specific kinase (MuSK). The gastrocnemius muscle of male adult Sprague–Dawley rats was isometrically exercised. Upon completion of muscle contraction, the rats were euthanized in the early (after 0, 1, 3, 6 or 24 h) and late (after 48 or 72 h) recovery phases and the gastrocnemius muscles were removed. Non‐exercised control animals were euthanized in the basal state (control group). In the early recovery phase, Agrn gene expression increased whereas LRP4 decreased without any change in the protein and gene expression of AChR gene subunits. In the late recovery phase, Agrn, Musk, Chrnb1, Chrnd and Chrne gene expression were altered and agrin and MuSK protein expression increased. Moreover, mTORC1 and protein kinase B/Akt‐histone deacetylase 4 (HDAC) were activated in the early phase but not in the late recovery phase. Furthermore, rapamycin, an inhibitor of mTORC1, did not disturb changes in AChR subunit gene expression after muscle contraction. However, rapamycin addition slightly increased AChR gene expression, while insulin did not impact it in rat L6 myotube. These results suggest that changes in the AChR subunits after muscle contraction are independent of the rapamycin‐sensitive mTORC1 pathway. What is the central question of this study?Can muscle contraction‐induced activation of mechanistic target of rapamycin complex 1 (mTORC1) be linked to changes in acetylcholine receptor (AChR) gene expression and molecular signalling for maintaining neuromuscular junctions (NMJs)?What is the main finding and its importance?An acute high‐intensity muscle contraction dynamically changes AChR gene expression and muscle‐specific kinase (MuSK) signalling proteins at the late recovery phase of the contraction. Additionally, pharmacological inhibition of mTORC1 via rapamycin does not affect muscle contraction‐induced alterations in AChR genes. Our findings indicate that an acute high‐intensity muscle contraction induces changes in MuSK signalling and mTORC1‐independent changes in expression of AChR genes. [ABSTRACT FROM AUTHOR]

Ribosome biogenesis is an important regulator of skeletal muscle hypertrophy induced by repeated bouts of resistance exercise (RE). Hot-water immersion (HWI), a widely used post-exercise recovery strategy, activates the mechanistic target of rapamycin (mTOR) signaling, a key regulator of ribosome biogenesis in skeletal muscle. However, the effect of HWI on skeletal muscle ribosome biogenesis is not well understood. Here, we aimed to investigate the effects of HWI and post-exercise HWI on ribosome biogenesis using a rat RE model. Male Sprague-Dawley rats were randomly assigned to HWI and non-HWI groups. In both groups, the right leg was isometrically exercised using transcutaneous electrical stimulation, while the left leg was used as an internal non-RE control. Following RE, both limbs were immersed in hot water (41.2 ± 0.03°C) for 20 min under isoflurane anesthesia in the HWI group and the gastrocnemius muscles were sampled at 3- and 24-h post-exercise. HWI significantly increased mTOR signaling and c-Myc mRNA expression, whereas post-exercise HWI significantly increased transcription initiation factor-IA mRNA expression. However, neither HWI nor post-exercise HWI enhanced 45S pre-rRNA expression, ribosomal RNA, or ribosomal protein content. In addition, HWI tended to decrease 28S rRNA and 18S rRNA content, widely used markers of ribosome content. These results suggest that HWI as a post-exercise recovery is not effective in activating ribosome biogenesis. NEW & NOTEWORTHY: Ribosome biogenesis is crucial in resistance exercise (RE)-induced skeletal muscle hypertrophy. This study examined the effects of hot-water immersion (HWI) on ribosome biogenesis after RE. HWI and post-exercise HWI increased c-Myc and transcription initiation factor-IA mRNA but did not alter ribosomal RNA transcription or ribosomal protein content. HWI tended to decrease 28S and 18S ribosomal RNA. These findings suggest that HWI, as a recovery strategy, does not effectively promote ribosome biogenesis or muscle protein synthesis. [ABSTRACT FROM AUTHOR]

Background and Aim Methods Results Conclusions Sarcopenia and osteoporosis adversely impact the clinical outcomes of patients with chronic liver disease (CLD). The Japan Society of Hepatology (JSH) sarcopenia criteria utilize bioelectrical impedance analysis (BIA) for assessing muscle mass rather than dual‐energy X‐ray absorptiometry (DXA), which can simultaneously diagnose these comorbidities. We investigated the correlations and interchangeability between the appendicular skeletal muscle mass index (ASMI) values determined using BIA and DXA and evaluated the diagnostic ability of DXA for sarcopenia and osteosarcopenia in patients with CLD.This cross‐sectional study included 173 patients with CLD. Sarcopenia was defined as low ASMIBIA according to the JSH and Asian Working Group for Sarcopenia (AWGS) criteria (ASMIBIA cutoff) or low ASMIDXA according to the AWGS criteria (ASMIDXA cutoff) and low handgrip strength. For women, a provisional cutoff value was set for ASMIDXA using the ASMIBIA cutoff (ASMIDXA‐altered cutoff).We found that ASMIBIA and ASMIDXA were significantly correlated (r = 0.921; P < 0.001). The Bland–Altman plots demonstrated substantial agreement between ASMIBIA and ASMIDXA, with a mean difference of 0.0116 kg/m2. The prevalence rates of sarcopenia and osteosarcopenia diagnosed using the ASMIBIA cutoff were 26.0% and 17.3%, respectively. The kappa coefficients for the prevalence of sarcopenia and osteosarcopenia were 0.759 and 0.775 between ASMIBIA cutoff and ASMIDXA cutoff and 0.780 and 0.806 between ASMIBIA cutoff and ASMIDXA‐altered cutoff, respectively.The utilization of DXA can facilitate the comprehensive assessment and management of musculoskeletal comorbidities in patients with CLD. [ABSTRACT FROM AUTHOR]

Wheelchair basketball players often develop shoulder pain due to repetitive wheelchair propulsion motion. Wheelchair propulsion involves two phases, push and recovery, with several different muscles simultaneously active in each phase. Although differences in the coordinated activity of multiple muscles may influence the mechanism of injury occurrence, there have been no studies investigating muscle synergy in wheelchair propulsion motion. Twelve healthy adult males with no previous wheelchair driving experience were included. The surface electromyography data of 10 muscles involved in shoulder joint movements were measured during a 20 m wheelchair propulsion motion. Muscle synergies were extracted using non-negative matrix factorization analysis of the electromyography data. Four muscle synergies were identified during wheelchair propulsion. Synergy 1 reflects propulsion through shoulder flexion and elbow flexion, while Synergy 2 involves shoulder flexion and elbow extension. Synergy 3 describes shoulder extension returning the upper limb, which has moved forward during the push, back to its original position, and Synergy 4 relates to stabilize the shoulder girdle during the recovery phase. This study is the first to explore muscle synergy during wheelchair propulsion, and the data from healthy participants without disabilities or pain will provide a baseline for future comparisons with data from wheelchair basketball players. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]