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Weakened Contractile Performance and Mitochondrial Respiratory Complex Activity in Skeletal Muscle Improve during Interbout Arousal in Hibernating Daurian Ground Squirrel, ISpermophilus dauricus/I
Mammalian hibernation is composed of multiple episodes of torpor bout, separated by phases of interbout arousal. During torpor, the skeletal muscles of mammals are undoubtedly inactive, but it has been proven to mitigate disuse atrophy. While interbout arousal has been implicated in the prevention of muscle atrophy, the underlying mechanisms sustaining muscle contraction remain to be explored. In the present study, Daurian ground squirrels (Spermophilus dauricus) were divided into four groups: pre-hibernation (PRE), torpor (TOR), interbout arousal (IBA), and post-hibernation (POST). The contractile performance of slow-twitch soleus muscle (SOL) and fast-twitch extensor digitorum longus muscle (EDL) was detected both in situ and in vitro. Concurrently, mitochondrial respiratory chain complex activity in these muscles was quantified. Our findings revealed that in situ contractile properties of both muscles, including force, power output, time duration, and force development/relaxation rates of twitch contraction, and force and power output of tetanic contraction declined in the TOR group compared to the PRE group, but improved in the IBA and POST groups. Fatigue resistance of muscles, determined by the power output of repetitive tetanic contractions in situ, decreased in the TOR group but recovered in the IBA and POST groups. In vitro studies demonstrated that tetanic contraction power output in isolated muscles increased with muscle temperature in both TOR and IBA groups. However, at the same temperature, power output was consistently lower in the TOR group compared to the IBA group. Moreover, the activity of the mitochondrial respiratory chain complex, especially Complexes I and II, decreased in the TOR group but showed recovery in the IBA and POST groups. These findings suggest that both the contractile performance and fatigue resistance of mammalian skeletal muscle are compromised during torpor but can be improved during interbout arousal and post-hibernation. The rebound in body temperature and rise in mitochondrial respiratory chain complex activity in skeletal muscle are involved in enhancing contractile performance and fatigue resistance. This study suggests that interbout arousal functions as a vital temporal interval during which skeletal muscles can transition from the inactivity induced by torpor to a state of restored contractile functionality. Thus, interbout arousal serves as a behavioral safeguard against disuse-induced damage to skeletal muscles during hibernation.
Journal Article
20 fun facts about the muscular system
\"Muscles do far more than help us lift heavy things off the ground. Muscles make the heart work well and move food through the stomach. They allow us to walk, swim, and even draw! In the fun fact file format, this book introduces readers to the most interesting aspects of the muscular system, including information from the science curriculum, through engaging and sometimes gross tidbits!\"-- Provided by publisher.
Book
The concise book of muscles
\"This newly revised fourth edition of The Concise Book of Muscles is a comprehensive guide to the major muscle groups. Fully illustrated with more than 500 drawings, and easy to use, this compact reference provides a complete profile for each muscle, clearly showing its origin, insertion, nerve supply, and action, the movements that use it, and, where appropriate, exercises that stretch and strengthen it. The book's distinctive quick-reference format shows students exactly how to locate and identify specific muscles, highlighting those that are heavily used and therefore subject to injury in a variety of sports and activities. Each muscle chapter now includes an overview of the gross anatomy of the body area to show bony landmarks, cross-sections of muscle layers, and points of attachment as well as a quick reference table and an overview of the nerve pathways that are most relevant. The book also includes a new chapter on the pelvic floor muscles--of particular interest to those studying or practicing yoga and Pilates--as well as a 20\"x35\" detachable muscle wall chart. \"--Amazon.com.
Book
Association of paraspinal muscle water–fat MRI-based measurements with isometric strength measurements
Objectives
Chemical shift encoding-based water–fat MRI derived proton density fat fraction (PDFF) of the paraspinal muscles has been emerging as a surrogate marker in subjects with sarcopenia, lower back pain, injuries and neuromuscular disorders. The present study investigates the performance of paraspinal muscle PDFF and cross-sectional area (CSA) in predicting isometric muscle strength.
Methods
Twenty-six healthy subjects (57.7% women; age: 30 ± 6 years) underwent 3T axial MRI of the lumbar spine using a six-echo 3D spoiled gradient echo sequence for chemical shift encoding-based water–fat separation. Erector spinae and psoas muscles were segmented bilaterally from L2 level to L5 level to determine CSA and PDFF. Muscle flexion and extension maximum isometric torque values [Nm] at the back were measured with an isokinetic dynamometer.
Results
Significant correlations between CSA and muscle strength measurements were observed for erector spinae muscle CSA (r = 0.40;
p
= 0.044) and psoas muscle CSA (r = 0.61;
p
= 0.001) with relative flexion strength. Erector spinae muscle PDFF correlated significantly with relative muscle strength (extension: r = -0.51;
p
= 0.008; flexion: r = -0.54;
p
= 0.005). Erector spinae muscle PDFF, but not CSA, remained a statistically significant (
p
< 0.05) predictor of relative extensor strength in multivariate regression models (R
2
adj
= 0.34;
p
= 0.002).
Conclusions
PDFF measurements improved the prediction of paraspinal muscle strength beyond CSA. Therefore, chemical shift encoding-based water–fat MRI may be used to detect subtle changes in the paraspinal muscle composition.
Key Points
• We investigated the association of paraspinal muscle fat fraction based on chemical shift encoding-based water–fat MRI with isometric strength measurements in healthy subjects.
• Erector spinae muscle PDFF correlated significantly with relative muscle strength.
• PDFF measurements improved prediction of paraspinal muscle strength beyond CSA.
Journal Article
Direct Isolation of Satellite Cells for Skeletal Muscle Regeneration
Muscle satellite cells contribute to muscle regeneration. We have used a Pax3[superscript GFP/+] mouse line to directly isolate (Pax3)(green fluorescent protein)-expressing muscle satellite cells, by flow cytometry from adult skeletal muscles, as a homogeneous population of small, nongranular, Pax7+, CD34+, CD45-, Sca1- cells. The flow cytometry parameters thus established enabled us to isolate satellite cells from wild-type muscles. Such cells, grafted into muscles of mdx nu/nu mice, contributed both to fiber repair and to the muscle satellite cell compartment. Expansion of these cells in culture before engraftment reduced their regenerative capacity.
Journal Article