Language：English   Publishing type：Research paper (scientific journal)  

In high-intensity and sprint interval training, the frequency of contractions is typically higher compared to moderate-intensity continuous training, but it remains unclear whether this contributes to the effective increase in fatigue resistance mechanisms. Here, we investigated the role of contraction frequency in high-intensity training on endurance adaptations of mouse skeletal muscle. Male C57BL/6 mice were divided into groups based on high (0.25 s contraction every 0.5 s) and low (0.25 s contraction every 4.5 s) contraction frequencies, with either 360 contractions per session (Hi360 and Lo360) or 30 contractions per session (Hi30 and Lo30). The plantar flexor muscles were stimulated using in vivo supramaximal electrical stimulation, where all muscle fibers were maximally activated, every other day for 5 weeks. In both the Hi360 and Lo360 groups, where force production declined to less than 40% of the initial value during the training session, muscle endurance, as well as mitochondrial content and respiratory capacity, were increased to a similar extent. In contrast, the rate of torque decline during the training session was more pronounced in the Hi30 group compared to the Lo30 group. In response, the Hi30 group, but not the Lo30 group, exhibited increased fatigue resistance and mitochondrial respiration, which was accompanied by increased PGC-1α expression and an activation of AMPK/Ulk1 pathway. These data suggest that the frequency of contractions is a critical factor in determining the efficient enhancement of mitochondrial respiratory capacity and muscle endurance through high-intensity training, presumably due to promotion of mitochondrial quality control.

DOI： 10.1152/japplphysiol.00530.2024

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Publishing type：Research paper (scientific journal)   Publisher：Wiley  

Abstract

Although platelet‐rich plasma (PRP) has been widely used regardless of the severity of muscle strain, there have been very few basic studies in which its effects on muscle injury were examined by using models that accurately mimic the clinical muscle strain injury process. Therefore, the aim of this study was to confirm by physiological and structural analyses whether PRP purified by a general preparation method has a muscle healing effect on muscle damage caused by eccentric contraction (ECC). Male Wistar rats were subjected to muscle injury induced by ECC in bilateral plantar flexor muscles using electrical stimulation and an automatically dorsiflexing footplate. The rats were randomly assigned to three groups by type of injection: phosphate‐buffered saline (PBS), leukocyte‐poor PRP (LP‐PRP), or leukocyte‐rich PRP (LR‐PRP) injection into gastrocnemius muscles three times at weekly intervals. The platelet concentrations of the LP‐PRP and LR‐PRP were three to five times higher than that of whole blood. The recovery process of torque strength in the plantar flexor muscle, signal changes in MRI images, and histological evaluation 3 weeks after injury showed no obvious differences among the three groups, and every muscle recovered well from the injury without marked fibrosis. The results that neither LP‐PRP nor LR‐PRP was found to accelerate healing of muscle injuries suggested that conventional preparation and use of PRP for simple muscle injuries caused by muscle strain should be carefully considered, and further basic research using models that accurately mimic clinical practice should be carried out to determine the optimal use of PRP.

DOI： 10.1002/jor.25784

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Language：English   Publishing type：Research paper (scientific journal)  

BACKGROUND: Exercise, especially high-intensity interval training (HIIT), can increase mitochondrial respiratory capacity and enhance muscular endurance, but its systemic burden makes it difficult to safely and continuously prescribe for patients with chronic kidney disease (CKD)-related cachexia who are in poor general condition. In this study, we examined whether HIIT using electrical stimulation (ES), which does not require whole-body exercise, improves muscle endurance in the skeletal muscle of 5/6 nephrectomized rats, a widely used animal model for CKD-related cachexia. METHODS: Male Wistar rats (10 weeks old) were randomly assigned to a group of sham-operated (Sham) rats and a group of 5/6 nephrectomy (Nx) rats. HIIT was performed on plantar flexor muscles in vivo with supramaximal ES every other day for 4 weeks to assess muscle endurance, myosin heavy-chain isoforms, and mitochondrial respiratory function in Nx rats. A single session was also performed to identify upstream signaling pathways altered by HIIT using ES. RESULTS: In the non-trained plantar flexor muscles from Nx rats, the muscle endurance was significantly lower than that in plantar flexor muscles from Sham rats. The proportion of myosin heavy chain IIa/x, mitochondrial content, mitochondrial respiratory capacity, and formation of mitochondrial respiratory supercomplexes in the plantaris muscle were also significantly decreased in the non-trained plantar flexor muscles from Nx rats than compared to those in plantar flexor muscles from Sham rats. Treatment with HIIT using ES for Nx rats significantly improved these molecular and functional changes to the same degrees as those in Sham rats. Furthermore, a single session of HIIT with ES significantly increased the phosphorylation levels of AMP-activated protein kinase (AMPK) and p38 mitogen-activated protein kinase (MAPK), pathways that are essential for mitochondrial activation signaling by exercise, in the plantar muscles of both Nx and Sham rats. CONCLUSION: The findings suggest that HIIT using ES ameliorates muscle fatigue in Nx rats via restoration of mitochondrial respiratory dysfunction with activation of AMPK and p38 MAPK signaling. Our ES-based HIIT protocol can be performed without placing a burden on the whole body and be a promising intervention that is implemented even in conditions of reduced general performance status such as CKD-related cachexia.

DOI： 10.3389/fphys.2024.1423504

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Publishing type：Research paper (scientific journal)   Publisher：American Physiological Society  

Mitochondrial dysfunction is associated with decreased skeletal muscle endurance in chronic kidney disease (CKD), but the muscle physiological phenotype and major changes in intramuscular metabolites during muscle fatigue in CKD-related cachexia remain unclear. By using a 5/6 nephrectomized CKD rat model, the present study revealed that CKD is associated with reduced tetanic force in response to repetitive stimuli in a subacute phase, impaired mitochondrial respiration, and inadequate supply of acetyl-CoA during muscle fatigue.

DOI： 10.1152/japplphysiol.00226.2023

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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.bpj.2022.11.793

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Language：Japanese   Publisher：(公社)日本整形外科学会  

Ichushi

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Language：Japanese   Publisher：(一社)日本足の外科学会  

Ichushi

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Language：Japanese   Publisher：北海道整形災害外科学会  

Ichushi

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Language：Japanese   Publisher：(公社)日本整形外科学会  

Ichushi

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Language：Japanese   Publisher：(一社)日本関節鏡・膝・スポーツ整形外科学会  

Ichushi

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