Scott B Going

PMID: 8817362;Abstract:

OBJECTIVE: To assess the effect of variations in regional composition on the accuracy of dual-energy X-ray absorptiometry (DXA) in humans by placing packets of lard, water and ground beef, to simulate fat, very lean tissue and high density lean material, on the thighs and abdomen. SUBJECTS: 28 healthy males and females (mean age: 25 y; mean % fat: 24.6%). METHODS: Up to six consecutive total body DXA scans (baseline plus five scans with added packets) at 16 cm/s were performed on each subject (Lunar DPX-L, software version 1.3y). Eight conditions were examined: one lard packet (n = 18), two stacked lard packets, one ground beef packet and one water packet (all n = 10) alternately placed on the thighs and abdomen. Masses (kg) and percentage fats (% fat) of the lard, water and ground beef packets were 1.45 and 90%, 2.80 and 4% and 1.80 and 24%, respectively. RESULTS: Differences between actual (baseline plus packet) and measured composition were assessed using paired t-tests (p 0.05). Under all conditions except with two abdominal lard packets, actual and measured total mass were similar (p > 0.05). Percentage fat of one lard packet was significantly underestimated when placed on the abdomen (90% actual vs 52% measured). The % fat of two lard packets was underestimated when placed on the thighs (90% vs 77%) and abdomen (90% vs 47%) while the % fat of the water packet was overestimated in both locations. CONCLUSION: The Lunar DXA underestimates the % fat of lard placed over the abdomen moreso than when placed over the thighs and overestimates % fat of water in both locations independent of thickness. Ground beef is accurately detected.

PMID: 20401689;PMCID: PMC3817010;Abstract:

Genetic variations in the adrenergic receptor (ADR) have been associated with body composition in cross-sectional studies. Recent findings suggest that ADR variants may also modify body composition response to lifestyle. We assessed the role of ADR variants in body composition response to 12 months of resistance training versus control in previously sedentary postmenopausal women. Randomized trial completers were genotyped for A2B ^Glu9/12 by fragment length analysis, and B2 ^Gln27Glu and B3 ^Trp64Arg by TaqMan (n = 148, 54% hormone therapy users). Associations between genotypes and body composition, by dual energy X-ray absorptiometry, were analyzed using univariate models. There was no main effect of individual genes on change in body composition, however, gene × exercise interactions were observed for A2B ^Glu9/12 and B2 ^Gln27Glu on change in lean soft tissue (LST, p = 0.02); exercisers on the A2B ^Glu9- background gained LST compared to a loss among controls over 12 months (p 0.05), with no significant intervention effect on the A2B ^Glu9+ background. Similarly, there was a significant LST gain with exercise on the B2 ^Glu27+ background compared to loss among controls and no intervention effect on the B2 ^Glu27- background. A non-significant association between total body fat (TBF) and B3 ^Trp64Arg persisted among sedentary controls only when intervention groups were separated (%TBF gain with B3 ^Arg64+ carriage, p = 0.03); exercisers lost TBF regardless of genotype. In summary, effect modification by lifestyle was demonstrated on ADRA2B, B2, and B3 genetic backgrounds. Individuals with certain ADR genotypes may be more vulnerable to adverse changes in body composition with sedentary behavior, thus these candidate genes warrant further study. © 2010 Springer Science+Business Media, LLC.

PMID: 2708210;Abstract:

Whole-body bioelectrical impedance analysis (BIA) was evaluated for its reliability and accuracy in estimating body composition in children. The hypothesis that the index, body height² divided by resistance (RI), can accurately predict fat-free body mass (FFB) and percent fat (%FAT) in children was tested on 94 caucasian children 10-14 yr old. Criterion variables were FFB and %FAT estimated using multicomponent equations developed for children. BIA measurements (resistance and reactance) were found to be reliable. Prediction accuracy (standard error of the estimate, SEE) for FFB from RI alone was 2.6 kg and for %FAT from RI and body weight was 4.2%. For RI, anthropometric variables and reactance, the SEE improved to 1.9 kg FFB. For RI and anthropometric variables, the SEE was 3.3% FAT. For anthropometric variables alone, the SEE's were 2.1 kg FFB and 3.2% FAT. Adult FFB and %FAT prediction equations cross-validated with this sample resulted in SEE's similar to those for adult samples. We conclude that RI together with anthropometry is a reliable and an acceptably accurate method of estimating FFB mass and %FAT in children.

Abstract:

The purpose of our study was to characterize the vibration delivered by a whole-body vibration (WBV) exercise platform and quantify the acceleration transmissibility throughout the body during different WBV exercises. Our accelerometry-based experimental setup, includes materials and methods for assessing vibration frequencies and corresponding magnitudes both at the side-alternating vibration platform and on multiple anatomic landmarks of the subject's body. Fourteen subjects completed a sequence of four different exercises on the platform at different vibration frequencies. Results have shown that researchers/clinicians should verify the vibration characteristics of the platform before beginning its use. The information provided by the manufacturers can have limited utility when prescribing an exercise/rehabilitation program on a WBV platform. Vibration seems to be dampened while it travels the body distal to proximal, with maximal attenuation seen at the shoulder level. Different exercises seem to influence the vibration transmissibility to some extent. © 2011 IEEE.