Author
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Lukaski, Henry |
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Submitted to: Annals of the New York Academy of Sciences
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 10/22/1999 Publication Date: 5/1/2000 Citation: Lukaski, H.C. 2000. Assessing regional muscle mass with segmental measurements of bioelectrical impedance in obese women during weight loss. Annals of the New York Academy of Sciences. 904:154-158. Interpretive Summary: The routine assessment of protein status of an individual, either in national nutritional surveys or among hospitalized patients, is limited by the availability of methods that are safe, convenient, reliable and accurate. Historically, the use of measurements of upper arm circumference and a skinfold thickness has been employed with less than acceptable success, particularly in people who are obese and losing weight. We have implemented the use of a modification of the bioelectrical impedance method to assess the muscle mass of the right thigh of overweight women before and during controlled weight loss. By using small strip electrodes placed on the front of the thigh, we found a small decrease in muscle mass that was consistent with determinations made with dual x-ray absorptiometry. Importantly, the impedance estimates indicated only muscle whereas circumference measurements indicated fat loss. These findings show the value of the impedance method to track changes in localized muscle mass in people who are losing weight. This information will be useful to scientists and clinical practitioners who seek to monitor muscle mass in people who are gaining or losing body weight. Technical Abstract: Tetrapolar bioelectrical impedance analysis (BIA) offers the possibility of determining the bioconductor volume in discrete segments of the body because the resistivities of bone, fat and skeletal muscle differ considerably. We tested this hypothesis by measuring BIA and anthropometry of defined segments of the right thighs of women before and during a controlled weight loss program. Eight women, aged 22 to 32 yr with a body mass index of 37.8 +/- 1.6 (mean +/- SE) kg/m**2 underwent determinations of body composition with dual x-ray absorptiometry (DXA) and regional BIA measurements (800 uA at 50 kHz) before and monthly for 4 months during weight loss. BIA measurements were made with spot detector electrodes positioned 10 cm apart on the anterior of the thigh with source electrodes placed on the right hand and foot. The physical volume of the thigh segment decreased 29 +/- 3 % (p < 0.0001) with a modest change in its bioconductor volume (8 +/- 0.2 %; p < 0.05). Muscle (181 +/- 49 g; p < 0.05) and fat mass (702 +/- 95 g; p < 0.001) declined. Bioconductor volume correlated with DXA-determinations of muscle mass (r = 0.91, p < 0.0001) whereas physical volume correlated (r = 0.95, p < 0.0001) with fat mass. These findings support the hypothesis that BIA is a valid method to assess regional muscle mass in humans. |
