The sections in this article are:


1
Motor Unit
1.1
Fibers per Motor Unit

1.2
Contractile Properties

1.3
Biochemical Basis for Differences in Twitch Properties

1.4
Histochemical Differentiation of Muscle Fibers

1.5
Ultrastructural Basis for Skeletal Muscle Fiber Typing

1.6
Maximal Contractile Force

1.7
Speed of Contraction

1.8
Fatigue Characteristics

1.9
Metabolic Characteristics

1.10
Ionic Composition of Skeletal Muscle

1.11
Summary




2
Muscle Fiber Composition in Human Skeletal Muscle

3
Motor-Unit Recruitment

4
Adaptive Response in Skeletal Muscle
4.1
Muscle Size

4.2
Metabolic Capacity




5
Connective Tissue

6
Capillaries
6.1
Methodology

6.2
Anatomy

6.3
Capillary Density

6.4
Capillary Length and Diameter

6.5
Use and Disuse

6.6
Regulation




7
Significance of Adaptation
7.1
Muscular Size

7.2
Substrate Stores

7.3
Enzyme Activities

7.4
Summary

Skeletal Muscle Adaptability: Significance for Metabolism and Performance

Muscle type and fiber type specificity in muscle wasting

Skeletal muscle fibres as factors for pork quality

Chronic treatment of rats with clenbuterol, a beta 2-receptor agonist (8–12 wk), caused hypertrophy of histochemically identified fast- but not slow-twitch fibers within the soleus, while the mean areas of both fiber types were increased in the extensor digitorum longus (EDL). In contrast, treatment with the beta 2-receptor antagonist, butoxamine, reduced fast-twitch fiber size in both muscles. In the solei and to a lesser extent in the EDLs, the ratio of the number of fast- to slow-twitch fibers was increased by clenbuterol, while the opposite was observed with butoxamine. The muscle fiber hypertrophy observed in the EDL was accompanied by parallel increases in maximal tetanic tension and muscle cross-sectional area, while in the solei, progressive increases in rates of force development and relaxation toward values typical of fast-twitch muscles were also observed. Our results suggest a role of beta 2-receptors in regulating muscle fiber type composition as well as growth.

Slow to fast alterations in skeletal muscle fibers caused by clenbuterol, a beta 2-receptor agonist

Krause MP, Riddell MC, Hawke TJ. Effects of type 1 diabetes mellitus on skeletal muscle: clinical observations and physiological mechanisms.

Effects of type 1 diabetes mellitus on skeletal muscle: clinical observations and physiological mechanisms

The response of rat gastrocnemius muscle fibers to chronic streptozotocin-diabetes was studied. Transverse sections of this muscle from normal and diabetic rats were histochemically assayed for reduced diphosphopyridine nucleotide-diaphorase, myofibrillar adenosine triphosphatase, mitochondrial alpha-glycerophosphate dehydrogenase, beta-hydroxybutyrate dehydrogenase, and alkaline phosphatase activities. Cross-sectional areas of the fiber types were measured, and fiber capillarization and populations estimated. Chemically-induced diabetes appeared to have little effect on the metabolic or morphological properties of slow-twitch fibers. However, a general dedifferentiation occurred in the 2 fast-twitch fiber populations. There was a loss of oxidative potential in the fast-twitch-oxidative-glycolytic fibers, and a significant decrease in size in the fast-twitch-glycolytic fibers. No change in the proportions of slow- and fast-twitch fibers in the muscles of diabetic rats occurred. It is concluded that hypoinsulinism has differential effects on the 3 fiber types in heterogeneous rat skeletal muscle, and that slow-twitch fibers are least affected by the diabetic condition.

P. D. Gollnick

Papers

Histochemical properties of skeletal muscle fibers in streptozotocin-diabetic rats.