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Cited by 156Muscle activation and electromyography studiesMuscle Physiology and DisordersCardiovascular and exercise physiology

Factors causing difference in force output among motor units in the rat medial gastrocnemius muscle

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Kanda, K, Hashizume, K·1992·The Journal of Physiology
DOI 10.1113/jphysiol.1992.sp019064PMC PMC1176222
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Abstract

1. The isometric contractile properties and morphological characteristics of the muscle unit portion of motor units were investigated in the medial gastrocnemius (MG) muscle of Fischer 344 rats. Individual motor units were functionally isolated by stimulating single MG axons in finely dissected ventral root filaments. 2. To study the mechanical properties of the motor units in the rat MG muscle, ninety-six motor units in five animals were classified into three categories (type FF, FR and S units) using two physiological criteria: presence or absence of the 'sag' property and fatigability. The relative distribution of the different motor unit types in the sample was 35.4% for type FF, 47.9% for type FR, and 16.7% for type S units. 3. There was little overlap in the distribution of twitch contraction time between type F (including types FF and FR) and type S units. The mean value was 17.1 ms for type FF, 15.7 ms for type FR, and 28.0 ms for type S units. Type FF units produced the largest tetanic tension (mean +/- S.D.; 201 +/- 75 mN). Tension output of type S units was the smallest (15 +/- 6 mN), and that of type FR units was intermediate (100 +/- 45 mN). These values were significantly different. 4. A muscle unit portion of twenty-three motor units (8 FF, 6 FR, and 9 S units) was depleted of its glycogen through repetitive stimulation after characterization of its mechanical properties. Cross-sectional areas of units fibres and innervation ratio were directly measured in sections stained for glycogen using a periodic and acid-Schiff (PAS) reaction. Specific tension of unit fibres was calculated by dividing the maximum tetanic tension of a unit by its total fibre area. 5. The number of unit fibres ranged from 44 to 77 for type S, 116 to 198 for type FR, and 221 to 356 for type FF units, and differences among their means (66, 154 and 271, respectively) were significant. Tetanic tension was correlated with innervation ratio for all of the twenty-three units, or units within a particular type. 6. Mean fibre area for type S units (1983 microns2) was significantly smaller than that for type FF units (3489 microns2). Fibres belonging to type FR units had an intermediate size (2648 microns2). Correlation between tetanic tension and fibre area was significant for either all units or units within a particular type. 7. Total cross-sectional area was significantly different among the motor unit types, and was highly correlated to the maximum tetanic tension.(ABSTRACT TRUNCATED AT 400 WORDS)

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  • MG is thought to be recruited by larger diameter axons than those that innervate LG and soleus, which reduces its activation threshold.

    “MG is thought to be recruited by larger diameter axons than those that innervate LG and soleus, which reduces its activation threshold [53].”

    From Directed stimulation with interfascicular interfaces for peripheral nerve stimulation (2021) · cites this paper as [53]

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Authors
Kanda, K., & Hashizume, K.
Affiliations
Tokyo Metropolitan Institute of Gerontology (JP)
Venue
The Journal of Physiology
Publisher
Wiley
Published
1992-03
Volume
448
Issue
1
Pages
677-695
ISSN
  • 0022-3751 (ISSN-L)
  • 1469-7793
DOI
10.1113/jphysiol.1992.sp019064
PMC
PMC1176222
OpenAlex
W2160719507
Cited by
156
References
47
Citations by year
2025: 5 · 2024: 1 · 2023: 3 · 2022: 5 · 2021: 8 · 2020: 2 · 2019: 5 · 2018: 3 · 2017: 4 · 2016: 7 · 2015: 9 · 2014: 4 · 2013: 3 · 2012: 6
FWCI
3.77
Type
journal article
Language
en
Open access
Licence
onlinelibrary.wiley.com/termsAndConditions#vor (vor)
Locations
  • The Journal of Physiology (publishedVersion)
  • PubMed Central (publishedVersion)
  • PubMed (publishedVersion)
Topics
  • Physical Sciences › Engineering › Biomedical Engineering › Muscle activation and electromyography studies
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Muscle Physiology and Disorders
  • Health Sciences › Medicine › Complementary and alternative medicine › Cardiovascular and exercise physiology
Keywords
motor units, medial gastrocnemius, output force, twitch contraction time, tetanic tension, glycogen depletion, fiber cross-sectional area, specific tension, motor unit fatigue, rat skeletal muscle, ventral root stimulation
MeSH terms
Animals, Electric Stimulation, Male, Motor Neurons, Muscle Contraction, Muscles, Neural Conduction, Rats, Inbred F344, Rats

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