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- Lexell, Jan, et al.
(författare)
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Differences in fiber number and fiber type proportion within fascicles : A quantitative morphological study of whole vastus lateralis muscle from childhood to old age.
- 1992
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Ingår i: Anatomical Record. - : Wiley. - 0003-276X .- 1097-0185. ; 234:2, s. 183-189
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Tidskriftsartikel (refereegranskat)abstract
- Data are presented on the number of fibers and the proportion of different fiber types within fascicles of whole vastus lateralis muscles from 5 male children, 5 to 15 years of age, and compared with results from 25 male adults, middle aged and old individuals. The results verify a difference in the proportion of fibers with different properties within a fascicle. The proportion of type 2 (fast twitch) fibers on the border of fascicles is larger than the proportion internally: the children have (P less than 0.01) greater difference than the adults and the middle aged, whereas the old have (P less than 0.001) less difference than the other age groups. The mean number of fibers per fascicle increases (P less than 0.05) from childhood to adult age, and thereafter reduces (P less than 0.01). The results imply that fascicles continuously rearrange during the normal growth and development and the normal aging process. It is argued that the causes of the difference in fiber type proportions within fascicles are local factors in the muscle, secondary to the overall age related functional demands put on the fiber population.
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| 2. |
- Lexell, Jan, et al.
(författare)
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Growth and development of human muscle : a quantitative morphological study of whole vastus lateralis from childhood to adult age
- 1992
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Ingår i: Muscle and Nerve. - : Wiley. - 0148-639X .- 1097-4598. ; 15:3, s. 404-409
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Tidskriftsartikel (refereegranskat)abstract
- The mechanisms underlying the increase in volume of muscle tissue, and the functional development of muscle fibers from childhood through adolescence to adult age, have been studied. Cross sections of autopsied whole vastus lateralis muscle from 22 previously physically healthy males, 5 to 37 years of age, were prepared enzyme histochemically (myofibrillar ATPase) and examined morphometrically. The data obtained on muscle cross-sectional area, size, total number, and proportion of type 1 (slow-twitch) and type 2 (fast-twitch) fibers were analyzed using linear regression techniques. The results show that the increase in muscle cross-sectional area from childhood to adult age is caused by an increase in mean fiber size. This is accompanied by a functional development of the fiber population: the proportion of type 2 fibers increases significantly from the age of 5 (approx. 35%) to the age of 20 (approx. 50%), which, in the absence of any discernible effect on the total number of fibers, is most likely caused by a transformation of type 1 to type 2 fibers.
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| 3. |
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| 4. |
- Sjöström, Michael, et al.
(författare)
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Evidence of fibre hyperplasia in human skeletal muscles from healthy young men? : A left-right comparison of the fibre number in whole anterior tibialis muscles
- 1991
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Ingår i: European Journal of Applied Physiology and Occupational Physiology. - 0301-5548 .- 1432-1025. ; 62:5, s. 301-304
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Tidskriftsartikel (refereegranskat)abstract
- Cross-sections (thickness 10 microns) of whole autopsied left and right anterior tibialis muscles of seven young previously healthy right-handed men (mean age 23 years, range 18-32 years) were prepared for light-microscope enzyme histochemistry. Muscle cross-sectional area and total number of fibres, mean fibre size (indirectly determined) and proportion of the different fibre types (type 1 and type 2 on basis of myofibrillar adenosine triphosphatase characteristics), in each muscle cross-section were determined. The analysis showed that the cross-sectional area of the left muscle was significantly larger (P less than 0.05), and the total number of fibres was significantly higher (P less than 0.05), than for the corresponding right muscle. There was no significant difference for the mean fibre size or the proportion of the two fibre types. The results imply that long-term asymmetrical low-level daily demands on muscles of the left and the right lower leg in right-handed individuals provide enough stimuli to induce an enlargement of the muscles on the left side, and that this enlargement is due to an increase in the number of muscle fibres (fibre hyperplasia). Calculations based on the data also explain why the underlying process of hyperplasia is difficult, or even impossible, to detect in standard muscle biopsies.
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