E. Siglinsky

Total Body Less Head Measurement Is Most Appropriate for Lean Mass Assessment in Adults

Exclusion of the head from total-body dual-energy X-ray absorptiometry (DXA) scans is recommended when measuring pediatric bone mass (1,2). We write to suggest that a similar approach, that is, total body less head (TBLH) measurement, should be considered when measuring total-body lean mass in adults. DXA-measured total-body lean mass is often used as a surrogate for muscle mass in athletic performance settings and sometimes in clinical research studies. However, it is essential to appreciate that DXA lean mass is not simply a measurement of muscle; indeed, DXA fat-free mass is largely water (3). Consequently, up to ~10% of DXA-measured whole-body lean mass is located in the head, presumably primarily a measurement of water within the brain. As such, the head constitutes a region that contributes little to skeletal muscle function/physical performance and could not be expected to be altered by exercise regimens or pharmacological approaches designed to improve muscle mass and physical performance. To explore the potential importance of this phenomenon, we assessed the proportion of total-body lean mass contained within the head region on DXA totalbody scans in adults across the life span. Initially, we evaluated DXA total-body scans in 112 men and women aged ≥70 yr (mean age 80.6 ± 6.0). In this group, the proportion of lean mass located in the head (mean [standard deviation]) was 7.3% (1.0), ranging from 4.7% to 9.2%. The percentage of lean mass in the head was negatively correlated with total-body lean mass using linear regression analysis (i.e., as lean mass declines, the proportion located in the head increases; Fig. 1; r = 0.71, p < 0.0001). To further explore potential age relationships, the percent head lean mass was calculated in a younger cohort (n = 610) composed of a convenience sample from a midlife US aging study, MIDUS (4), and a group of university athletes. This cohort was arbitrarily divided as young (ages 19 to <40 yr) and middle age (≥40 to 65 yr). Mean head lean mass was 5.6% and 6.3% in the young and middle-aged groups, respectively. The percentage of lean mass within the head differed between these 3 age groups by analysis of variance (p < 0.0001). Similar to the initial observation made in older adults, linear regression demonstrated a negative correlation of percent head lean mass with whole-body lean mass in the entire cohort (r = 0.75, p < 0.0001). The 2 clinical studies were approved by the University of Wisconsin Health Sciences internal review board and student athlete data were classified as exempt. We believe it is important that athletic trainers, clinicians, and researchers using DXA to monitor exercise interventions appreciate this phenomenon and consider the use of TBLH lean mass as such interventions will have little to no effect on head lean mass. A similar approach may be even more important in studies of older adults with sarcopenia. Indeed it is plausible that the higher percentage of lean mass located in the head region among older adults who have lower total lean mass potentially indicates that head lean mass (likely primarily water within the brain) is largely retained with advancing age, whereas lean mass elsewhere (presumably largely muscle) declines. Since the proportion of head lean mass is greatest in those with lowest muscle mass (the group targeted for therapeutic sarcopenia interventions), including a larger amount of “lean mass” that cannot be altered by muscle building therapies seems destined to impair the ability of such therapies to have a beneficial effect. In conclusion, the head can account for up to 10% of whole-body lean mass in individuals’ aged ≥70 yr. Exclusion of head lean mass is appropriate when total-body DXA is used as a surrogate for muscle mass in settings where interventions are being undertaken to enhance muscle mass. The option to select TBLH in total-body DXA scans should not be limited to the pediatric age range.

Comparison of muscle/lean mass measurement methods: correlation with functional and biochemical testing

SummaryDXA-measured lean mass is often used to assess muscle mass but has limitations. Thus, we compared DXA lean mass with two novel methods—bioelectric impedance spectroscopy and creatine (methyl-d3) dilution. The examined methodologies did not measure lean mass similarly and the correlation with muscle biomarkers/function varied.IntroductionMuscle function tests predict adverse health outcomes better than lean mass measurement. This may reflect limitations of current mass measurement methods. Newer approaches, e.g., bioelectric impedance spectroscopy (BIS) and creatine (methyl-d3) dilution (D3-C), may more accurately assess muscle mass. We hypothesized that BIS and D3-C measured muscle mass would better correlate with function and bone/muscle biomarkers than DXA measured lean mass.MethodsEvaluations of muscle/lean mass, function, and serum biomarkers were obtained in older community-dwelling adults. Mass was assessed by DXA, BIS, and orally administered D3-C. Grip strength, timed up and go, and jump power were examined. Potential muscle/bone serum biomarkers were measured. Mass measurements were compared with functional and serum data using regression analyses; differences between techniques were determined by paired t tests.ResultsMean (SD) age of the 112 (89F/23M) participants was 80.6 (6.0) years. The lean/muscle mass assessments were correlated (.57–.88) but differed (p < 0.0001) from one another with DXA total body less head being highest at 37.8 (7.3) kg, D3-C muscle mass at 21.1 (4.6) kg, and BIS total body intracellular water at 17.4 (3.5) kg. All mass assessment methods correlated with grip strength and jump power (R = 0.35–0.63, p < 0.0002), but not with gait speed or repeat chair rise. Lean mass measures were unrelated to the serum biomarkers measured.ConclusionsThese three methodologies do not similarly measure muscle/lean mass and should not be viewed as being equivalent. Functional tests assessing maximal muscle strength/power (grip strength and jump power) correlated with all mass measures whereas gait speed was not. None of the selected serum measures correlated with mass. Efforts to optimize muscle mass assessment and identify their relationships with health outcomes are needed.

Do Textiles Impact DXA Bone Density or Body Composition Results

External artifacts can confound dual-energy X-ray absorptiometry (DXA) measurements. It is often accepted that garments free of metal do not affect DXA results; however, little data exist in this regard. It is plausible that some textiles absorb radiation and thereby alter DXA results. We hypothesized that some dense or synthetic textiles, for example, reflective materials, might alter DXA-measured bone and soft tissue mass. Hologic and GE Lunar spine phantoms and a Bioclinica prototype total body phantom were imaged on a GE Lunar iDXA and Prodigy densitometer. Each phantom was scanned 10 times to establish mean values. Subsequently, 2 layers of various fabrics were placed over the entire top surface of the phantom, and 10 scans were performed without repositioning. Samples of natural, synthetic, or embellished fabric (including those with reflective material) and of varying thickness were used. Wilcoxon signed rank tests were used to compare the means between bare phantom and textile-covered phantom. Significant differences were demonstrated often, depending on the scanner, phantom, and textile used. A polyester fabric with reflective strip consistently altered measurements. For example, this fabric increased measured mean lumbar spine bone mineral density and total body bone mineral content by 0.008 g/cm2 and 3.6 g, respectively (p < 0.01). Similarly, mean total body fat decreased (-173 g) and lean mass increased (+213 g; p < 0.01). Fat and lean mass were also affected by metallic thread, wool, blend denim, and shiny polyester (p < 0.05), and lean mass was affected by cotton denim and sweatshirt material (p < 0.0003). In conclusion, textiles can affect DXA-measured bone mineral density and body composition results. Even small amounts of reflective material could alter mass measurements by ~25% of the least significant change. Clothing made of dense textiles (e.g., wool and denim) or those with reflective material and metallic thread should be avoided during DXA scanning.

Psychosocial Factors Associated With Reduced Muscle Mass, Strength, and Function in Residential Care Apartment Complex Residents

Sarcopenia is a major source of disability in older adults. However, limited data are available about sarcopenia components (i.e., muscle mass, strength, and function) and their relationship to psychosocial factors among older adults living in residential care apartment complexes (RCACs). The current study examined muscle mass, strength, and function and explored their relationship to self-efficacy for exercise, depressive symptoms, and social support in 31 RCAC residents. RCAC residents had lower muscle mass, strength, and function compared to values reported in studies of community-dwelling older adults. Men had higher muscle mass and strength than women. The current findings showed a trend for individuals with high self-efficacy, without depressive symptoms, and with strong social support to present numerically greater muscle mass, strength, and function. Further studies with larger samples are needed to confirm the current study findings and inform development of interventions implemented in RCAC settings. [Res Gerontol Nurs. 2018; 11(5):238-248.].