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Decline in isokinetic force with age: muscle cross-sectional area and specific force (1997)

Jubrias, S. A. ; Odderson, I. R. ; Esselman, Peter C. ; [et al.]

Springer

Pflügers Archiv 434 (1997), S. 246-253

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ISSN: 1432-2013

Keywords: Key words MVC maximum voluntary contraction ; Myosin heavy chains ; Magnetic resonance imaging

Source: Springer Online Journal Archives 1860-2000

Topics: Medicine

Notes: Abstract Humans produce less muscle force (F) as they age. However, the relationship between decreased force and muscle cross-sectional area (CSA) in older humans is not well documented. We examined changes in F and CSA to determine the relative contributions of muscle atrophy and specific force (F/CSA) to declining force production in aging humans. The proportions of myosin heavy chain (MHC) isoforms were characterized to assess whether this was related to changes in specific force with age. We measured the peak force of isokinetic knee extension in 57 males and females aged 23–80 years, and used magnetic resonance imaging to determine the contractile area of the quadriceps muscle. Analysis of MHC isoforms taken from biopsies of the vastus lateralis muscle showed no relation to specific force. F, CSA, and F/CSA decreased with age. Smaller CSA accounted for only about half of the 39% drop in force that occurred between ages 65–80 years. Specific force dropped about 1.5% per year in this age range, for a total decrease of 21%. Thus, quantitative changes in muscle (atrophy) are not sufficient to explain the strength loss associated with aging.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s004240050392

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Electrical discontinuity of tissue substitute models at 27.12 MHz (1983)

Lehmann, Justus F. ; McDougall, John A. ; Guy, Arthur W. ; [et al.]

New York, NY [u.a.] : Wiley-Blackwell

Bioelectromagnetics 4 (1983), S. 257-265

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ISSN: 0197-8462

Keywords: shortwave ; diathermy applicators ; heating ; attenuation ; conductivity ; Life and Medical Sciences ; Occupational Health and Environmental Toxicology

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Biology , Physics

Notes: Tissue-substitute models consisting of layers of synthetic, electrically equivalent subcutaneous fat, muscle, and bone shaped in conformation with the normal anatomy are used for rapid determination of distribution of temperature and specific absorption rate throughout the tissues when exposed to electromagnetic radiation. The surfaces of the bisected models are approximated during a short exposure period, then separated and scanned with a thermograph. A method was developed to eliminate the electrical discontinuity at the bisected surfaces while allowing separation and subsequent thermographic scanning. A thin layer of silk screen wetted with propylene glycol saturated with sodium chloride was used at the fat interface and a 0.9% sodium chloride solution was used to wet the screen at the muscle interface to eliminate electrical discontinuity during exposure to 27.12-MHz diathermy. Tests showed that in the presence of an electrical discontinuity the heating pattern was grossly distorted. With the method used, the electrical discontinuity is minimized and the subsequent thermographic scanning reveals that the heating pattern is equivalent to that of an intact model.

Additional Material: 3 Ill.