Regional Soft Tissue Composition Research Articles

Body composition and disability in people with multiple sclerosis: A dual-energy x-ray absorptiometry study

IntroductionBody composition refers to the relative distribution of different tissue types within the body, including fat, lean, and bone tissues. There is evidence for associations between body composition and the development of multiple sclerosis (MS). The relationship between body composition and disease progression and disability accumulation, however, is unclear. ObjectivesTo examine: a) differences in overall and regional body composition by disability status in persons with multiple sclerosis (MS); and b) the relationship between body composition and other outcomes reflecting impairments and limitations due to MS. MethodsCross-sectional investigation of 47 ambulatory persons with relapsing remitting MS who were grouped by Expanded Disability Status Scale (EDSS) scores as having mild (1.0–4.0; n = 26) or moderate (4.5–6.5; n = 21) disability. Main outcome measures were whole-body and regional soft tissue composition (%body fat (BF), fat mass (FM), and fat-free soft tissue mass (FFM)), bone mineral content (BMC), and bone mineral density (BMD) determined from dual-energy X-ray absorptiometry (DXA). Other outcomes included physical fitness, mobility, cognitive processing speed, symptoms, and health-related quality of life (HRQOL). ResultsWhole-body and regional %BF and FM were significantly higher, and whole-body and appendicular BMC and BMD were significantly lower in participants with moderate disability than those with mild disability (all p < .05). There were no significant differences in whole-body or regional FFM by disability status. In the overall sample, body fat correlated significantly with cardiorespiratory fitness (prs = −.52 to −.56), pain symptoms (prs = .32), and psychological HRQOL (prs = .34). FFM (prs = .38–.48) and BMC (prs = .53–.69) correlated primarily with measures of muscular strength. ConclusionsPersons with MS who have greater disability present with higher body fat and lower bone tissue content and density than those with mild disability. These findings highlight the need for strategies that address potential changes in body composition with disability accumulation.

Knee extension strength in obese and nonobese male adolescents

The aim of the present study was to compare "absolute" and "relative" knee extension strength between obese and nonobese adolescents. Ten nonobese and 12 severely obese adolescent boys of similar chronological age, maturity status, and height were compared. Total body and regional soft tissue composition were determined using dual-energy X-ray absorptiometry (DXA). Knee extensors maximum voluntary contraction (MVC) torque was measured using an isometric dynamometer at a knee angle of 60° (0° is full extension). Absolute MVC torque was significantly higher in obese adolescents than in controls. However, although MVC torque expressed per unit of body mass was found to be significantly lower in obese adolescent boys, no significant difference in MVC torque was found between groups when normalized to fat-free mass. Conversely, when correcting for thigh lean mass and estimated thigh muscle mass, MVC torque was significantly higher in the obese group (17.9% and 22.2%, respectively; P <0.05). To conclude, our sample of obese adolescent boys had higher absolute and relative knee extension strength than our nonobese controls. However, further studies are required to ascertain whether or not relative strength, measured with more accurate in vivo methods such as magnetic resonance imaging, is higher in obese adolescents than in nonobese controls.

Estimation of Total-Body and Regional Soft Tissue Composition From DXA Bone Densitometry of the Lumbar Spine and Hip

The percent fat in soft tissues adjacent to the lumbar spine and proximal femur, which are required parameters in the calculation of bone mineral by conventional dual-energy X-ray absorptiometry (DXA) of the spine and hip, were analyzed for their relationship with the total-body soft tissue–scanning derivatives. The cohort (N = 149), consisting of stable actively treated male human immunodeficiency virus HIV-positive patients, was split in half to obtain prediction equations with one half to be validated by the other half. Prediction equations for the dependent variables total-body fat, total-body lean mass, trunk fat, total arm + leg fat, and leg fat were derived by step-down multiple regression. A Bland-Altman comparison of the predicted and observed values showed that the limits of agreement were too large to be clinically helpful. The correlations of the ratio of adjacent spine/hip fat with ratios of trunk/arm + leg fat and trunk/leg fat, markers of peripheral lipoatrophy in HIV, were 0.725 and 0.780, respectively. The 3 ratios were compared with the clinical diagnosis of the presence or absence of peripheral lipoatrophy by receiver operating characteristic analysis. The area under the curve was 0.720 for adjacent spine/hip fat ratio and 0.655 and 0.699 for trunk/arm + leg fat and trunk/leg fat, respectively; they were not significantly different. In conclusion, for male HIV-positive patients, the difference between predicted values and actual values rendered limits of agreement that were too wide to be clinically acceptable. The ratio of percent fat in the lumbar spine region to percent fat in the proximal femur region reflected the presence of peripheral lipoatrophy as effectively as the trunk/peripheral fat ratio that was derived from the total-body scan.

Reduced muscle strength and functional performance in men with prostate cancer undergoing androgen suppression: a comprehensive cross-sectional investigation

This study examined the effects of androgen suppression therapy (AST) on upper and lower body muscle strength and a range of direct measures of physical performance using a cross-sectional design with 118 men (48 men undertaking AST for prostate cancer and 70 healthy aged-matched controls) from a single tertiary center. Primary end points included muscle strength for the upper- and lower-body; functional performance--repeated chair rise, usual and fast 6-m walk, 6-m backwards walk and 400-m walk time; and dual-energy X-ray absorptiometry assessment--whole body, regional soft tissue composition and bone mineral density (BMD). Men on AST had significantly reduced muscle strength for the upper- and lower-body and impaired functional performance compared to controls (P<0.05). As expected, AST patients had significantly lower whole-body and hip BMD and higher percent of body fat than controls (P<0.05), and tended to have lower whole-body lean mass (-2.3 kg, P=0.077). Appendicular skeletal muscle was positively associated with upper-body (r=0.400-0.606, P<0.001) and lower-body (r=0.549-0.588, P<0.001) muscle strength, and strength was related to functional performance. Men undertaking AST were consistently impaired across a broad range of physical and functional musculoskeletal performance assessments compared with their age-matched normal controls. These findings are relevant for those patients considering AST for subclinical disease management, but whose physical reserve is marginal. Strategies to counter these adverse effects of AST need to be initiated so that independent living and quality of life can be maintained.

Discrimination between cases of hip fracture and controls is improved by hip structural analysis compared to areal bone mineral density. An ex vivo study of the femoral neck

In vivo bone densitometry is affected by measurement inaccuracies arising from the assumptions made about soft tissue and marrow composition. This study tested the hypothesis that section modulus (SM, a measure of bending resistance) when measured ex vivo, would discriminate cases of hip fracture from controls better than areal bone mineral density (aBMD). The biopsies were from ( n = 22, female) subjects that had suffered an intracapsular hip fracture. The control material ( n = 24, female) was from post-mortem subjects. Serial peripheral quantitative computed tomography (pQCT) 1-mm thick cross-sectional images of femoral neck previously embedded in methacrylate were obtained with the Densiscan 1000 pQCT densitometer and matched for lateral location. The image voxels were converted to units of bone mass, which were then used to derive the section modulus. The data were used to derive means from which receiver operating characteristic (ROC) curves could be generated. The area under the curves (AUC) showed that discrimination between the fracture cases and controls was better for SM than aBMD [SM: AUC = 0.83 (95% confidence interval: 0.71, 0.96), aBMD: AUC = 0.70 (0.54, 0.85); P = 0.034]. To simulate the forces experienced during a sideways fall, the model's neutral axis was rotated by 210°. The results for section modulus were predictable from those at 0° ( r 2 = 0.97). We conclude that biomechanical analysis of the distribution of bone within the femoral neck may offer a marked improvement in the ability to discriminate patients with an increased risk of intracapsular fracture. Progress towards implementing this form of analysis in clinical densitometry should improve its diagnostic value, but may depend in part on better image resolution and more accurate corrections for the variability between subjects in regional soft tissue composition.

Muscle strength and soft tissue composition as measured by dual energy x-ray absorptiometry in women aged 18-87 years.

Dual energy x-ray absorptiometry (DEXA) offers the possibility of assessing regional soft tissue composition, i.e. lean mass (LM) and fat mass: LM may be considered a measure of muscle mass. We examined age-related differences in LM, percentage fat (%fat) and muscle strength in 100 healthy non-athletic women aged 18-87 years. Relationships between muscle strength and leg LM in 20 elite female weight lifters and in 18 inactive women with previous hip fractures were also studied. The LM and %fat of the whole body, trunk, arms and legs were derived from a whole body DEXA scan. Isokinetic knee extensor strength (KES) and flexor strength (KFS) at 30 degrees.s-1 were assessed using an isokinetic dynamometer. The women aged 71-87 years had 35% lower KES and KFS than the women aged 18-40 years (P < 0.0001). Differences in LM were less pronounced. The LM of the legs, for instance, was 15% lower in the old than in the young women (P < 0.0001). In a multiple regression analysis with age, body mass, height and leg LM or KES as independent variables and KES or leg LM as the dependent variable, age was the most important predictor of KES (r(partial) = -0.74, P < 0.0001). The same applied to KFS. Body mass, not age, was the most important predictor of leg LM (r(partial) = 0.65, P < 0.0001) and of LM at all other measurement sites. The LM measured at different regions decreased equally with increasing age. The KES:leg LM ratio was negatively correlated with age (r = -0.70, P < 0.0001). The weight lifters had significantly higher KES:leg LM ratios than age-matched controls (+ 12%, P < 0.0001) and vice versa for the women with previous hip fractures (-36%, P < 0.0001). In conclusion, from our study it would seem that in healthy nonathletic women, age is a more important determinant of muscle strength than is LM as measured by DEXA. Muscle strengthening exercises and inactivity seem to have a considerably stronger influence on muscle strength than on LM.