The Role of Protein and Amino Acids in Sustaining and Enhancing Performance (1999) / Chapter Skim
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12 Skeletal Muscle Markers
12 Skeletal Muscle Markers
Pages 255-278
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From page 255... ...
However, with aging and obesity increased amounts of adipose tissue become interspersed between muscle bundles, and this composite structure is referred to as anatomic skeletal muscle (Wang et al., 1992; Heymsfield et al., 1995~. Some methods of measuring skeletal muscle mass rely on quantification of one or more of the components shown in the figure.
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From page 256... ...
S K, Lipid Adipocytes Adipose Na, Cl Tissue C Water Muscle Cells Non-Adipose Tissue Skeletal O Proteins Glycogen Extracellular Minerals Fluid Atomic Molecular Cellular Tissue-System FIGURE 12-1 Anatomic skeletal muscle components at the first four body composition levels.
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From page 257... ...
Broadly viewed, these properties are used with two types of models for deriving skeletal muscle mass estimates. The first model is a descriptive or type I model that shares in common the following characteristics: a reference method is used to estimate skeletal muscle mass in a well-defined subject group in whom the property is also measured; and a statistically derived component prediction equation is developed and then cross-validated in a new subject group (Wang et al., 1995~.
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From page 258... ...
Type Descriptive Mechanistic Anthropometry Skinfolds + + Circumferences Diameters Ultrasound Reflected sound waves + + BIA Resistance + Reactance + Urinary Metabolites Creatinine + 3-Methylhistidine + Imaging: · CT X-ray attenuation Cross-sectional area · MRI Proton relaxation times Cross-sectional area IVNA/Whole-body Total body N counting Total body K + NOTE: BIA, bioelectric impedance analysis; CT, computerized axial tomography; FFM, fat-free body mass; IVNA, in vivo neutron activation analysis; MRI, magnetic resonance Imaging.
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From page 259... ...
AVAILABLE METHODS Anthropometry Development of anthropometric skeletal muscle prediction methods are limited. There are also very few model-based anthropometric methods for estimating regional skeletal muscle mass.
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From page 260... ...
The important potential for developing anthropometric muscle estimation equations now exists due to the development of magnetic resonance imaging (MRI) muscle mass measurement methods (discussed in a later section)
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From page 261... ...
versus total body skeletal muscle volume measured by multislice MRI in 79 healthy adults. (Total muscle area [cm2]
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From page 262... ...
Appendicular and total body skeletal muscle can therefore potentially be estimated from measured extremity impedance or resistance by calibration against skeletal muscle mass using a reference method such as MRI or dual x-ray absorptionmetry (DXA)
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From page 263... ...
Although this information is preliminary, the potential for evaluating the muscle compartment of each limb separately and total appendicular skeletal muscle mass is evident. Work in this area is ongoing in this laboratory and at other research centers.
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From page 264... ...
This impedance approach can be used to estimate appendicular skeletal muscle mass. 100 90 80 70 60 50 N a, ~s :, 40 to I 30 20 10 o 0 10 20 30 40 Leg Ske leta I Muscle (kg)
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From page 265... ...
Although the data are limited, evidence supporting this hypothesis is reasonably good for healthy, weight-stable adults. A traditional concept has been that creatinine excretion is directly proportional to total body skeletal muscle mass (Heymsfield et al., 1983~.
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From page 266... ...
Main features of the 24-h urinary creatinine (Cr) method of estimating total body skeletal muscle mass (SM)
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From page 267... ...
FIGURE 12-9 Total body skeletal muscle mass measured by computerized tomography (CT)
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From page 268... ...
Multiple cross-sectional images can be used to reconstruct whole muscle groups or total body skeletal muscle mass. Imaging methods gather data in the form of picture elements or "pixels." Addition of thickness to the pixel creates a volume element or "voxel." When the outer and inner edges of a muscle group are traced on the system scanner, the enclosed pixels include myofibers, nerves, adipocytes, and other components, which collectively are referred to as anatomic skeletal muscle (Figure 12-1~.
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From page 269... ...
The enclosed area within a traced muscle includes entrapped adipose tissue, a component that increases on a relative basis with some diseases and advancing age. Careful manual tracing with the scanner's computerized track-ball device allows exclusion of obvious adipose tissue, and more complex pixel separation algorithms are also possible.
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From page 270... ...
Appendicular skeletal muscle is about 75 percent of total body skeletal muscle mass (Figure 12-12) , and this fraction is assumed stable within and SO ASH ASK | / CT FIGURE 12-12 Appendicular Skeletal Muscle Mass DXA Method.
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From page 271... ...
Repeated measurements by DXA of appendicular lean muscle mass indicated technical errors for arm, leg, and total body skeletal muscle of 7.0 2.4 percent, 2.4 ~ 0.5 percent, and 3.0 ~ 1.S percent, respectively (Clasey et al., 1997~. More research is needed in establishing comparability of body composition estimates across manufacturers and in evaluating if, and to what = 50 `~, 45 `,' 40 3 35 _ .
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From page 272... ...
for skeletal muscle based on chemical analysis of biopsies in subject groups ranging in age from newborns to adults. Hence, for a low cost and with minimal radiation exposure, DXA allows quantification of a large proportion of total body muscle mass.
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From page 273... ...
The applied model assumes stable TBK/TBN ratios of muscle and nonmuscle lean mass components. body skeletal muscle derived by the Burkinshaw-Cohn model and total body skeletal muscle by CT in healthy men and men with acquired immunodeficiency syndrome (AIDS)
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From page 274... ...
Observed temporal changes can reflect, for example, alterations in intramuscular adipose tissue at the tissue system level or in water and glycogen at the molecular level. A change in anthropometrically- or ultrasound-derived muscle mass may therefore not always reflect parallel changes in the main component of interest, muscle proteins.
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From page 275... ...
The relative safety and increasing availability of DXA makes it a good choice for longitudinal studies of skeletal muscle mass. However, some concerns are arising on the validity of DXA body composition measurements carried out over time, and more studies are needed to examine the validity of longitudinal DXA skeletal muscle mass estimates.
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From page 276... ...
1990. Appendicular skeletal muscle mass: Measurement by dual-photon absorptiometry.
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From page 277... ...
1996a. Total body skeletal muscle mass: Evaluation of 24 hour urinary creatinine excretion method by computerized axial tomography.
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