Regional skeletal muscle measurement: evaluation of new dual-energy X-ray absorptiometry model

Estimation of thigh muscle mass with magnetic resonance imaging in older adults and people with chronic obstructive pulmonary disease

BACKGROUND AND PURPOSE

Quantifying muscle mass is an essential part of physical therapy assessment, particularly in older adults and in people with chronic conditions associated with muscle atrophy. The purposes of this study were to examine the relationship between muscle cross-sectional area (CSA) and volume by use of magnetic resonance imaging (MRI) and to compare anthropometric estimations of midthigh CSA with measurements obtained from MRI.

SUBJECTS AND METHODS

Twenty older adults who were healthy and 20 people with chronic obstructive pulmonary disease (COPD), matched for age, sex, and body mass index, underwent MRI to obtain measurements of thigh muscle CSA and volume. Anthropometric measurements (skinfold thickness and thigh circumference) were used to estimate midthigh CSA.

RESULTS

Muscle volumes were significantly lower in the people with COPD than in the older adults who were healthy. Moderate to high correlations were found between midthigh CSA and volume in both groups (r=.61-.94). Anthropometric measurements tended to overestimate midthigh CSA in both the people with COPD (estimated CSA=64.9+/-17.8; actual CSA=48.3+/-10.2 cm(2)) and the older adults who were healthy (estimated quadriceps femoris muscle CSA=65.0+/-14.0; actual CSA=56.8+/-13.5 cm(2)). Furthermore, the estimated quadriceps femoris muscle CSAs were not sensitive enough to detect a difference in muscle size between people with COPD and controls. Thigh circumference alone was not different between groups and showed only low to moderate correlations with muscle volume (r=.19-.47).

DISCUSSION AND CONCLUSION

Muscle CSA measured from a single slice provides a good indication of volume, but the most representative slice should be chosen on the basis of the muscle group of interest. Thigh circumference is not correlated with muscle volume and, therefore, should not be used as an indicator of muscle size. The development of population-specific reference equations for estimating muscle CSA from anthropometric measurements is warranted.

Thyroxine therapy in euthyroid patients does not affect body composition or muscular function

OBJECTIVE

The main objective of the study was to evaluate the effects of small increments in thyroxine (T4) levels following levothyroxine (L-T4) administration on the body composition of women patients. The secondary objective was to assess the effect of the therapy on energy expenditure and muscular function.

METHODS

The prospective, randomized study consisted of a 12-month follow-up of 37 women with thyroid nodules. The patients were divided into two groups for comparison, one treated with L-T4 (20 women) and the other untreated (17 women). L-T4 dose was individually adjusted to obtain a serum thyroid-stimulating hormone in the lower portion of the normal range. Multiple tests, including bioelectrical impedance analysis, dual-energy X-ray absorptiometry, air displacement plethysmography, measurement of waist circumference, and skinfold anthropometry, were used to investigate the muscular, fat, and water compartments; energy expenditure and muscular function were assessed by cycle ergometry.

RESULTS

There were no significant differences in body composition, heart rate, energy metabolism, or muscular function between the group of women treated with L-T4 and the untreated group.

CONCLUSION

The controlled increase of circulating T4 does not appear to modify the body composition or muscular function in women patients.

Estimation of thigh muscle cross-sectional area by dual-energy X-ray absorptiometry in frail elderly patients

BACKGROUND

Thigh muscle mass and cross-sectional area (CSA) are useful indexes of sarcopenia and the response to treatment in older patients. Current criterion methods are computed tomography (CT) and magnetic resonance imaging.

OBJECTIVE

The objective was to compare thigh muscle mass estimated by dual-energy X-ray absorptiometry (DXA), a less expensive and more accessible method, with thigh muscle CSA determined by CT in a group of elderly patients recovering from hip fracture.

DESIGN

Midthigh muscle CSA (in cm(2)) was assessed from a 1-mm CT slice and midthigh muscle mass (g) from a 1.3-cm DXA slice in 30 patients (24 women) aged 81 +/- 8 y during 12 mo of follow-up. Fat-to-lean soft tissue ratios were calculated with each technique to permit direct comparison of a variable in the same units.

RESULTS

Baseline midthigh muscle CSA was highly correlated with midthigh muscle mass (r = 0.86, P < 0.001) such that DXA predicted CT-determined CSA with an SEE of 10 cm(2) (an error of approximately 12% of the mean CSA value). CT- and DXA-determined ratios of midthigh fat to lean mass were similarly related (intraclass correlation coefficient = 0.87, P < 0.001). When data were expressed as the changes from baseline to follow-up, CT and DXA changes were weakly correlated (intraclass correlation coefficient = 0.51, P = 0.019).

CONCLUSIONS

Assessment of sarcopenia by DXA midthigh slice is a potential low-radiation, accessible alternative to CT scanning of older patients. The errors inherent in this technique indicate, however, that it should be applied to groups of patients rather than to individuals or to evaluate the response to interventions.

Can dual energy X-ray absorptiometry provide a valid assessment of changes in thigh muscle mass with strength training in older adults?

OBJECTIVE

To determine how dual-energy X-ray absorptiometry (DXA) compares to computed tomography (CT) for measuring changes in total thigh skeletal muscle (SM) mass with strength training (ST) in older adults.

SUBJECTS

Fifty previously sedentary, relatively healthy older men (n=23, 60 (s.d.=7.5) years) and women (n=27, 60 (s.d.=9.3) years).

RESULTS

Results indicate that there was a significant increase in thigh SM mass with ST measured by both CT (3.9+/-0.4%) and DXA (2.9+/-0.6%) methods (both P<0.001), and there was not a significant difference in percent change between the two methods, although there was a substantial absolute difference ( approximately 2 kg) at baseline between the two methods. Although Bland-Altman plots indicate overall agreement between the percent thigh SM mass changes of DXA vs CT methods, the 3.4% error associated with DXA was greater than the thigh SM mass change from DXA. However, the CT measured change in thigh SM mass was greater than its error (0.6%).

CONCLUSIONS

DXA overestimates baseline and after ST thigh SM mass, and may not be able to detect small changes in thigh SM mass with ST due to its higher error. Although DXA has certain advantages that warrant is used in epidemiologic and intervention studies, improvements to DXA are needed for the accurate assessment of small changes in thigh SM mass.

Regional fat deposition as a factor in FFA metabolism

Humans have a large variability in body fat distribution, which has tremendous implications for metabolic health. Obese individuals with an upper-body-fat distribution have increased health complications such as dyslipidemia, hypertension, insulin resistance, and type 2 diabetes in comparison with lower-body-obese individuals. Additionally, females have more body fat, a greater proportion of fat in their lower body, and much less visceral fat than do lean males at the same body mass index. The reasons for these differences in body fat distribution have not been clearly identified but could be important. Herein we review what has been learned about regional differences in triglyceride storage capacity and lipolysis as they relate to the causes and consequences of regional fat accumulation. Both sex and site differences in regional fat storage have been described. In contrast, with the exception of variations between men and women in the contribution of visceral adipose tissue to hepatic FFA delivery, most studies have failed to show important sex differences in regional lipolysis in vivo.

Muscle quality, aerobic fitness and fat mass predict lower-extremity physical function in community-dwelling older adults

BACKGROUND

Muscle mass, strength and fitness play a role in lower-extremity physical function (LEPF) in older adults; however, the relationships remain inadequately characterized.

OBJECTIVE

This study aimed to examine the relationships between leg mineral free lean mass (MFLM(LEG)), leg muscle quality (leg strength normalized for MFLM(LEG)), adiposity, aerobic fitness and LEPF in community-dwelling healthy elderly subjects.

METHODS

Fifty-five older adults (69.3 +/- 5.5 years, 36 females, 19 males) were assessed for leg strength using an isokinetic dynamometer, body composition by dual energy X-ray absorptiometry and aerobic fitness via a treadmill maximal oxygen consumption test. LEPF was assessed using computerized dynamic posturography and stair ascent/descent, a timed up-and-go task and a 7-meter walk with and without an obstacle.

RESULTS

Muscle strength, muscle quality and aerobic fitness were similarly correlated with static LEPF tests (r range 0.27-0.40, p < 0.05); however, the strength of the independent predictors was not robust with explained variance ranging from 9 to 16%. Muscle quality was the strongest correlate of all dynamic LEPF tests (r range 0.54-0.65, p < 0.001). Using stepwise linear regression analysis, muscle quality was the strongest independent predictor of dynamic physical function explaining 29-42% of the variance (p < 0.001), whereas aerobic fitness or body fat mass explained 5-6% of the variance (p < 0.05) depending on performance measure.

CONCLUSIONS

Muscle quality is the most important predictor, and aerobic fitness and fat mass are secondary predictors of LEPF in community-dwelling older adults. These findings support the importance of exercise, especially strength training, for optimal body composition, and maintenance of strength and physical function in older adults.

Accuracy of eight-polar bioelectrical impedance analysis for the assessment of total and appendicular body composition in peritoneal dialysis patients

OBJECTIVE

To establish the accuracy of bioelectrical impedance analysis (BIA) for the assessment of total and appendicular body composition in peritoneal dialysis (PD) patients.

DESIGN

Cross-sectional study.

SETTING

University Nephrology Clinic.

SUBJECTS

In all, 20 PD patients and 77 healthy controls matched for gender, age and body mass index.

METHODS

Whole-body fat-free mass (FFM) and appendicular lean tissue mass (LTM) were measured by dual-energy X-ray absorptiometry. Resistance (R) of arms, trunk and legs was measured by eight-polar BIA at frequencies of 5, 50, 250 and 500 kHz. Whole-body resistance was calculated as the sum of R of arms, trunk and legs. The resistance index (RI) was calculated as the ratio between squared height and whole-body or segmental R.

RESULTS

RI at 500 kHz was the best predictor of FFM, LTM(arm) and LTM(leg) in both PD patients and controls. Equations developed on controls overestimated FFM and LTM(arm) and underestimated LTM(leg) when applied to PD patients. Specific equations were thus developed for PD patients. Using these equations, the percent root mean-squared errors of the estimate for PD patients vs controls were 5 vs 6% for FFM, 8 vs 8% for LTM(arm) and 7 vs 8% for LTM(leg).

CONCLUSION

Eight-polar BIA offers accurate estimates of total and appendicular body composition in PD patients, provided that population-specific equations are used.

A DXA study of muscle-bone relationships in the whole body and limbs of 2512 normal men and pre- and post-menopausal women

A whole-body DXA study of 1450 healthy Caucasian individuals [Bone 22 (1998) 683] found that mineral mass, either crude (BMC) or statistically adjusted to fat mass (FM-adjusted BMC), correlated linearly with lean mass (LM, proportional to muscle mass). The results showed similar slopes but decreasing intercepts (ordinate values) in the order: pre-MP women > men > post-MP women > children. This supports the hypothesis that sex hormones influence the control of bone status by muscle strength in all species. Now we further study those relationships in 2512 healthy Hispanic adults (307 men, 753 pre-MP women, 1452 post-MP women), including separate determinations in their upper and lower limbs. The slopes of the BMC or FM-adjusted BMC vs. LM relationships were parallel in all the studied regions. However, region-related differences were found between the ordinates of the curves. In the whole body, the crude-BMC/LM relationships showed the same ordinate differences as previously observed. In the lower limbs, those differences were smaller in magnitude but highly significant, showing the order: pre-MP women > men = post-MP women. In the upper limbs, the decreasing ordinate order was: men > pre-MP women > post-MP women. After fat adjustment of the BMC, order in both limbs was: men > pre-MP women > post-MP women. Parallelism of the curves was maintained in all cases. LM had a larger independent influence on these results than FM, body weight, or age. The parallelism of the curves supports the idea that a common biomechanical control of bones by muscles occurs in humans. Results suggest that sex-hormone-associated differences in DXA-assessed muscle-bone proportionality in humans could vary according to the region studied. This could be related to the different weight-bearing nature of the musculoskeletal structures studied. Besides the obvious anthropometric associations, FM would exert a mechanical effect as a component of body weight, evident in the lower limbs, while muscle contractions would induce a more significant, dynamical effect in both lower and upper limbs. Muscles seem to exert a larger influence than FM, body weight, and age on BMC in the whole body and lower limbs, regardless of the gender and reproductive status of the individual. The muscle-bone relationships studied may provide a rationale for a future differential diagnosis between disuse-related and other types of osteopenia.

Effect of fitness on arm vascular and metabolic responses to upper body exercise

We investigated arm perfusion and metabolism during upper body exercise. Eight average, fit subjects and seven rowers, mean ± SE maximal oxygen uptake (V̇o2 max) 157 ± 7 and 223 ± 14 ml O2· kg–0.73·min–1, respectively, performed incremental arm cranking to exhaustion. Arm blood flow (ABF) was measured with thermodilution and arm muscle mass was estimated by dual-energy X-ray absorptiometry. During maximal arm cranking, pulmonary V̇o2 was ∼45% higher in the rowers compared with the untrained subjects and peak ABF was 6.44 ± 0.40 and 4.55 ± 0.26 l/min, respectively ( P < 0.05). The arm muscle mass for the rowers and the untrained subjects was 3.5 ± 0.4 and 3.3 ± 0.1 kg, i.e., arm perfusion was 1.9 ± 0.2 and 1.4 ± 0.1 l blood·kg–1·min–1, respectively ( P < 0.05). The arteriovenous O2 difference was 156 ± 7 and 120 ± 8 ml/l, respectively, and arm V̇o2 was 0.98 ± 0.08 and 0.60 ± 0.04 l/min corresponding with 281 ± 22 and 181 ± 12 ml/kg, while arm O2 diffusional conductance was 49.9 ± 4.3 and 18.6 ± 3.2 ml·min–1·mmHg–1, respectively ( P < 0.05). Also, lactate release in the rowers was almost three times higher than in the untrained subjects (26.4 ± 1.1 vs. 9.5 ± 0.4 mmol/min, P < 0.05). The energy requirement of an ∼50% larger arm work capacity after long-term arm endurance training is covered by an ∼60% increase in aerobic metabolism and an almost tripling of the anaerobic capacity.

Disuse atrophy and exercise rehabilitation in humans profoundly affects the expression of genes associated with the regulation of skeletal muscle mass

Skeletal muscle atrophy occurs as a consequence of injury, illness, surgery, and muscle disuse, impacting appreciably on health care costs and patient quality of life, particularly in the absence of appropriate rehabilitation. The molecular mechanisms that regulate muscle mass during atrophy and rehabilitation in humans have not been elucidated, despite several robust candidate pathways being identified. Here, we induced skeletal muscle atrophy in healthy volunteers using two weeks of limb immobilization, and then stimulated the restoration of muscle mass with six weeks of supervised exercise rehabilitation. We determined muscle mass and function and performed targeted gene expression analysis at prescribed time points during immobilization and rehabilitation. For the first time, we have identified novel changes in gene expression following immobilization-induced atrophy and during a program of rehabilitative exercise that restored muscle mass and function. Furthermore, we have shown that exercise performed immediately following immobilization induces profound changes in the expression of a number of genes in favor of the restoration of muscle mass, within 24 h. This information will be of considerable importance to our understanding of how immobilization and contraction stimulate muscle atrophy and hypertrophy, respectively, and to the development of novel therapeutic strategies aimed at maintaining or restoring muscle mass.

Control of the Size of the Human Muscle Mass

This review is divided into two parts, the first dealing with the cell and molecular biology of muscle in terms of growth and wasting and the second being an account of current knowledge of physiological mechanisms involved in the alteration of size of the human muscle mass. Wherever possible, attempts have been made to interrelate the information in each part and to provide the most likely explanation for phenomena that are currently only partially understood. The review should be of interest to cell and molecular biologists who know little of human muscle physiology and to physicians, physiotherapists, and kinesiologists who may be familiar with the gross behavior of human muscle but wish to understand more about the underlying mechanisms of change.

Validation of a bioelectrical impedance analysis equation to predict appendicular skeletal muscle mass (ASMM)

RATIONALE

Appendicular skeletal muscle mass (ASMM) is useful in the evaluation of nutritional status because it reflects the body muscle protein mass. The purpose of this study was to validate, against dual-energy X-ray absorptiometry (DEXA), a BIA equation to predict ASMM to be used in volunteers and patients.

METHOD

Healthy men (n = 246 men, BMI 25.3+/-2.9 kg/m(2)) and women (n =198, 24.1+/-3.6 kg/m(2)), and heart, lung and liver transplant patients (213 men, BMI of 24.6+/-4.4 kg/m(2); 113 women, BMI 23.0+/-5.2 kg/m(2)) were measured by BIA (Xitron Technologies) and DEXA (Hologic QDR 4500). A BIA equation to predict ASMM (kg) that included height(2)/resistance, weight, gender, age and reactance, was developed by means of multiple regressions. [table: see text] Mean difference (Bland-Altman) for volunteers was 0.1+/-1.1 kg, r =0.95, SEE 1.12 kg and for patients -0.4+/-1.5 kg, r =0.91, SEE 1.5 kg. Best fitted multiple regression equation was -4.211 + (0.267 x height2 / resistance) + (0.095 x weight)+(1.909 x sex (men = 1, women = 0)) + (-0.012 x age) + (0.058 x reactance).

CONCLUSIONS

BIA permits the prediction of ASMM in healthy volunteers and patients between 22 and 94 years of age. A slightly larger, though clinically not significant, error was noted in patients.

Assessment of skeletal muscle mass in men with spinal cord injury using dual-energy X-ray absorptiometry and magnetic resonance imaging

The purpose of this study was to determine whether the proportion of skeletal muscle in the fat-free soft tissue mass (FFST) is the same in men with spinal cord injury (SCI) and able-bodied controls. Skeletal muscle mass and FFST of the midthigh were determined by using magnetic resonance imaging and dual-energy X-ray absorptiometry, respectively, in men with long-term (>2 yr) complete SCI (n = 8) and able-bodied controls of similar age, height, and weight (n = 8). Muscle mass (1.36 +/- 0.77 vs. 2.44 +/- 0.47 kg) and FFST (1.70 +/- 0.94 vs. 2.73 +/- 0.80 kg) were lower in the SCI group than in the controls (P < 0.05), but the lower ratio of muscle to FFST in the SCI group (0.80 +/- 0.09 vs. 0.91 +/- 0.10, P < 0.05) suggested that they had a lower proportion of muscle in the FFST than in controls. This notion was supported by analysis of covariance, in that the mean muscle adjusted to the mean FFST of the groups combined was lower in the SCI group. Despite the lower proportion of muscle in the FFST of the SCI group, the relation between muscle and FFST was strong in the SCI group (r = 0.99) and controls (r = 0.96). The findings suggest a disproportionate loss of muscle in the paralyzed thighs after SCI relative to other nonfat constituents, which may be accurately estimated in men with long-term SCI by dual-energy X-ray absorptiometry if the lower proportion of muscle in the FFST (approximately 15%) is taken into account.

Comparison of bioelectrical impedance analysis and dual-energy X-ray absorptiometry for the assessment of appendicular body composition in anorexic women

OBJECTIVE

To establish the accuracy of bioelectrical impedance analysis (BIA) for the assessment of appendicular body composition in anorexic women.

DESIGN

Cross-sectional study.

SETTING

Outpatient University Clinic.

SUBJECTS

A total of 39 anorexic and 25 control women with a mean (s.d.) age of 21 (3) y.

METHODS

Total, arm and leg fat-free mass (FFM) were measured by dual-energy X-ray absorptiometry and predicted from total and segmental BIA at 50 kHz. The predictor variable was the resistance index (Rl), that is, the ratio of height (2) to body resistance for the whole body and the ratio of length(2)/limb resistance for the arm and leg.

RESULTS

Predictive equations developed on controls overestimated total, arm and leg FFM in anorexics (P<0.0001). Population-specific equations gave a satisfactory estimate of total and appendicular FFM in anorexics (P=NS) but had higher percent root mean square errors (RMSEs%) as compared to those developed on controls (8% vs 5% for whole body, 12% vs 10% for arm and 10% vs 8% for leg). The accuracy of the estimate of total and leg FFM in anorexics was improved by adding body weight (Wt) as a predictor with Rl (RMSE%=5% vs 8% and 7% vs 10%, respectively). However, the same accuracy was obtained using Wt alone, suggesting that in anorexics, BIA at 50 kHz is not superior to Wt for assessing total and leg FFM.

CONCLUSION

BIA shows some potential for the assessment of appendicular body composition in anorexic women. However, Wt is preferable to BIA at 50 kHz on practical grounds. Further studies should consider whether frequencies >50 kHz give better estimates of appendicular composition in anorexics as compared to Wt.

SPONSORSHIP

University of Napoli.

Body composition and energy expenditure: relationship and changes in obese subjects before and after biliopancreatic diversion

Changes in total and segmental body composition were studied in 101 obese women before and 2, 6, 12, and 24 months after biliopancreatic diversion (BPD) and data 24 months after surgery were matched to 53 control subjects. The patients were studied by anthropometry, indirect calorimetry, and double-emission x-ray absorptiometry (DXA). The combination of calorimetry and body composition analysis allowed estimation of visceral and muscle lean mass. We observed a significant (analysis of variance [ANOVA]: P <.05) progressive reduction of fat and lean body mass (LBM) following BPD, with stabilization of both parameters between 12 and 24 months at levels not different from controls. Fat loss was significant in the arms, legs, and trunk segments. After 24 months, there was no significant difference in segmental fat mass between post-BPD patients and controls. Calorimetric data seem to confirm lean body mass (LBM) reduction. Visceral lean mass (kg) was significantly reduced from 8.1 +/- 2.2 in obese subjects to 6.5 +/- 1.8 in post-BPD patients at 24 months (P <.05); the control value was 7.2 +/- 1.8. Muscular lean mass (kg) was also significantly reduced, from 50.2 +/- 5.8 to 39.8 +/- 5.7 in the same subjects (P <.05), with a control value of 42.5 +/- 5.9. The decrease in muscle and visceral LBM reached control values without significant differences. Viscera/muscle ratio in pre-BPD patients was preserved in post-BPD patients at 24 months, but it was reduced during weight loss. Body composition studies showed a logarithmic relationship between fat and lean mass and a physiological contribution of lean mass to weight loss in the BPD patients. In conclusion, weight loss after BPD was achieved with an appropriate decline of LBM and with all parameters reaching, at stable weight, values similar to weight-matched controls.

Variations in percentage of body fat within different BMI groups in young, middle-aged and old women

OBJECTIVES

The objective of the present study was to characterize age-dependent variations in percentage of body fat within different body mass index (BMI) classes in healthy Danish women.

DESIGN

Cross-sectional analysis.

SETTINGS

The study was done at the Center for Clinical and Basic Research, Ballerup, Denmark.

SUBJECTS

Four hundred and four healthy women aged 18-75 years were included in the present study.

MEASUREMENTS

Fat tissue mass was estimated using dual-energy X-ray absorptiometry. Menopausal status and physical characteristics were also registered.

RESULTS

Mean values of percentage of body fat calculated in the normal and overweight BMI groups were higher in middle-aged and old women compared with young women. No significant differences were seen in the underweight and obese BMI groups. The cut-off levels between normal and overweight and between overweight and obesity were 35-43% and 40-50%, respectively.

CONCLUSION

The percentage of body fat is dependent on both age and menopausal status within each of the following BMI classes: from 20 to 25 and from 25 to 30, further emphasizing that BMI has limitations when used generally as an indicator of body fatness, and argues for defining BMI cut-off values age-specifically.

Volume estimates by imaging methods: model comparisons with visible woman as the reference

OBJECTIVE

To compare the accuracy of four volume estimation models to actual tissue and organ volumes measured in the visible woman.

METHODS

Actual volumes were calculated from 1-mm-thick visible woman images that were segmented for five major components including subcutaneous and visceral adipose tissue across the 1730 available slices. Four available models resolved to two equations: truncated cone/truncated pyramid vs. two-column/parallel trapezium. Between-slice interval and initial slice were systematically varied when deriving component volumes using the two equations in four regions.

RESULTS

For each compartment and each between-slice interval, the means of the two-column model were always the same as the corresponding reference volumes, whereas those of the truncated cone model were smaller than the reference volumes. Similarly, the coefficient variation for the two-column model was always smaller than for the truncated cone model.

DISCUSSION

The equation based on the parallel trapezium and the two-column models is more accurate in estimating tissue volumes than the corresponding equation for truncated pyramid and truncated cone models. This finding has important implications for the volume calculations of imaging-based body compartments such as adipose tissue.

Whole-body skeletal muscle mass: development and validation of total-body potassium prediction models

BACKGROUND

A substantial proportion of total body potassium (TBK) in humans is found in skeletal muscle (SM), thus affording a means of predicting total-body SM from whole-body counter-measured (40)K. There are now > 30 whole-body counters worldwide that have large cross-sectional and longitudinal TBK databases.

OBJECTIVE

We explored 2 SM prediction approaches, one based on the assumption that the ratio of TBK to SM is stable in healthy adults and the other on a multiple regression TBK-SM prediction equation.

DESIGN

Healthy subjects aged >or= 20 y were recruited for body-composition evaluation. TBK and SM were measured by whole-body (40)K counting and multislice magnetic resonance imaging, respectively. A conceptual model with empirically derived data was developed to link TBK and adipose tissue-free SM as the ratio of TBK to SM.

RESULTS

A total of 300 subjects (139 men and 161 women) of various ethnicities with a mean (+/- SD) body mass index (in kg/m(2)) of 25.1 +/- 5.4 met the study entry criteria. The mean conceptual model-derived TBK-SM ratio was 122 mmol/kg, which was comparable to the measurement-derived TBK-SM ratios in men and women (119.9 +/- 6.7 and 118.7 +/- 8.4 mmol/kg, respectively), although the ratio tended to be lower in subjects aged >or= 70 y. A strong linear correlation was observed between TBK and SM (r = 0.98, P < 0.001), with sex, race, and age as small but significant prediction model covariates.

CONCLUSIONS

Two different types of prediction models were developed that provide validated approaches for estimating SM mass from (40)K measurements by whole-body counting. These methods afford an opportunity to predict SM mass from TBK data collected in healthy adults.

Prevalence of sarcopenia and predictors of skeletal muscle mass in healthy, older men and women

BACKGROUND

Sarcopenia refers to the loss of skeletal muscle mass with age. The objective of this study was to determine the prevalence of sarcopenia in a population of older, community-dwelling research volunteers.

METHODS

Appendicular skeletal muscle mass was measured by dual x-ray absorptiometry in 195 women aged 64 to 93 years and 142 men aged 64 to 92 years. We defined sarcopenia as appendicular skeletal muscle mass/height(2) (square meters) less than 2 standard deviations below the mean for young, healthy reference populations. We used two different reference populations and compared prevalence in our population to that reported in previous studies. Body mass index (BMI) was calculated and physical activity and performance were measured with the Physical Activity Scale for the Elderly, the Short Physical Performance Battery, and the Physical Performance Test. We measured health-related quality of life by using the SF-36 general health survey. Serum estrone, estradiol, sex hormone-binding globulin, parathyroid hormone, and 25-hydroxy vitamin D were measured in all participants and bioavailable testosterone was measured only in men. Leg press strength and leg press power were determined in men.

RESULTS

The prevalence of sarcopenia in our cohort was 22.6% in women and 26.8% in men. A subgroup analysis of women and men 80 years or older revealed prevalence rates of 31.0% and 52.9%, respectively. In women, skeletal muscle mass correlated significantly with BMI and levels of serum estrone, estradiol, and 25-hydroxy vitamin D; in men, it correlated significantly with BMI, single leg stance time, leg press strength, leg press power, SF-36 general health score, Physical Performance Test total score, and bioavailable testosterone levels. With the use of linear regression analysis, BMI was the only predictor of appendicular skeletal muscle mass in women, accounting for 47.9% of the variance (p <.05). In men, BMI accounted for 50.1%, mean strength accounted for 10.3%, mean power accounted for 4.1%, and bioavailable testosterone accounted for 2.6% of the variance in appendicular skeletal muscle mass (p <.05).

CONCLUSIONS

Sarcopenia is common in adults over the age of 65 years and increases with age. BMI is a strong predictor of skeletal muscle mass in women and men. Strength, power, and bioavailable testosterone are further contributors in men. These data suggest that interventions to target nutrition, strength training, and testosterone replacement therapy should be further investigated for their role in preventing muscle loss with age.

Total-body skeletal muscle mass: estimation by a new dual-energy X-ray absorptiometry method

BACKGROUND

Skeletal muscle (SM) is an important body-composition component that remains difficult and impractical to quantify by most investigators outside of specialized research centers. A large proportion of total-body SM is found in the extremities, and a large proportion of extremity lean soft tissue is SM. A strong link should thus exist between appendicular lean soft tissue (ALST) mass and total-body SM mass.

OBJECTIVE

The objective was to develop prediction models linking ALST estimated by dual-energy X-ray absorptiometry (DXA) with total-body SM quantified by multislice magnetic resonance imaging in healthy adults.

DESIGN

ALST and total-body SM were evaluated with a cross-sectional design in adults [body mass index (in kg/m(2)) < 35] with an SM-prediction model developed and validated in model-development and model-validation groups, respectively. The model-development and model-validation groups included 321 and 93 ethnically diverse adults, respectively.

RESULTS

ALST alone was highly correlated with total-body SM (model 1: R(2) = 0.96, SEE = 1.63 kg, P < 0.001), although multiple regression analyses showed 2 additional predictor variables: age (model 2: 2-variable combined R(2) = 0.96, SEE = 1.58 kg, P < 0.001) and sex (model 3: 3-variable combined R(2) = 0.96, SEE = 1.58 kg, P < 0.001). All 3 models performed well in the validation group. An SM-prediction model based on the SM-ALST ratio was also developed, although this model had limitations when it was applied across all subjects.

CONCLUSION

Total-body SM can be accurately predicted from DXA-estimated ALST, thus affording a practical means of quantifying the large and clinically important SM compartment.

The effect of hormone replacement therapy on appendicular lean tissue mass in early postmenopausal women

OBJECTIVE

The impact of hormone replacement therapy (HRT) on skeletal muscle mass is still a controversial issue in women's health. Some authors hypothesize anabolic effects, others catabolic. These hypotheses, however, await confirmation by longitudinal observations based on more direct measurements of muscle mass. The aim of the present preliminary study was to evaluate the effect of a 3-year HRT program on appendicular lean tissue mass (LTM(A)) in early postmenopausal women aged 45-54 years.

DESIGN

This was a randomized, double-blind and placebo-controlled trial. Women received HRT with 2 mg estradiol valerate combined either continuously with 1 mg cyproterone acetate (days 1-28; n = 15) or sequentially with 75 mug levonorgestrel (days 17-28; n = 15), or placebo (n = 18). Serum estradiol was measured by radioimmunoassay. LTM(A) was measured by dual photon absorptiometry (baseline) and dual energy X-ray absorptiometry (years 2 and 3).

RESULTS

Baseline serum estradiol did not show significant correlation with the respective LTM(A) (r = 0.018, p = 0.88, n = 75). Cross-sectional analysis found no significant differences between the intervention groups at any time points. The longitudinal changes between years 2 and 3 showed a trend toward decreasing LTM(A) in those receiving HRT (-0.08 +/- 0.12 kg, n = 30) compared to those receiving placebo (0.12 +/- 0.25 kg, n = 18, p = 0.44).

CONCLUSIONS

The present preliminary study did not find significant effects on LTM(A) caused by HRT. The trends toward decreasing LTM(A) in the HRT groups might suggest catabolic rather than anabolic effects. These trends, however, await confirmation by larger clinical trials.

The evaluation of metabolic function and fat redistribution in clinical trials

Changes in lipid and carbohydrate metabolism and in body composition associated with the most potent and effective therapies available are being reported with increasing frequency. These changes could potentially lead to increased risks of cardiovascular disease. Clinical trials set up to investigate new antiretroviral therapies need to explore the therapies' impact on these potentially serious adverse outcomes, at least in a subset of patients. The measurements that are feasible to include for all patients clearly differ from those required by a metabolic substudy. We propose the following: firstly, a minimal set of parameters that should be included in all trials; secondly, a desirable set of parameters that should be included whenever possible; and thirdly, a list of exploratory measures that should be considered. These exploratory measures are classified by the different mechanisms for changes in body composition or weight: endocrinal, cardiovascular, sterol and chemokine/cytokine pathways. Standardized instruments for evaluating patients' reports of body changes and potential methods for assessing the risk of cardiovascular disease are described. Minimum and desirable standards for methods of measurement are also proposed. The choice of parameters is based on expert clinical opinion. The experts consulted include investigators from four large ongoing clinical trials with substudies specifically designed to investigate lipid and carbohydrate metabolism and changes in body composition, together with standard parameters for measurement within individual mechanistic pathways. The parameters proposed should be kept under review as the body of knowledge about metabolic function and fat redistribution in HIV infection increases.

Effect of highly active antiretroviral therapy on fat, lean, and bone mass in HIV-seropositive men and women

BACKGROUND

Alterations in body composition have been reported in HIV-positive adults receiving highly active antiretroviral therapy (HAART), but the magnitude and potential determinants of these changes are unclear.

OBJECTIVE

We compared total and regional body composition, as measured by dual-energy X-ray absorptiometry, in 203 HIV-positive men and 62 HIV-positive women according to HAART.

DESIGN

This was a cross-sectional analysis of a cohort study of nutrition and HIV infection.

RESULTS

After adjustment for age, weight, race, and exercise habits, total weight and fat mass did not differ significantly in men or women by HAART. Trunk fat was greater in men (1.0 kg; P < 0.001) and women (1.4 kg; P = 0.005) and leg fat was lower in men (-1.0 kg; P < 0.001) and women (-1.5 kg, P = 0.005) receiving HAART than in those not. This corresponded to a greater percentage of total fat mass located in the trunk (men: 7.5%, P < 0.001; women: 5.1%, P = 0.02). Lean mass was also greater with longer duration of HAART in men (P < 0.002). In men receiving HAART, total and regional bone mineral content were less than in the men not receiving HAART (P < 0.001). These effects increased with longer duration of HAART. Protease inhibitors were associated with the largest differences in regional fat.

CONCLUSIONS

HAART is associated with redistribution of fat mass from the legs to the trunk, despite no significant differences in total fat mass or weight. In men, HAART is also associated with a reduction in bone mineral content, suggesting that HAART increases the risk of central obesity and osteoporosis.

Determinants of bone mineral density in older men and women: body composition as mediator

This study aimed to assess the relative importance of several determinants of bone mineral density (BMD) and to examine to what extent these potential determinants influence total hip BMD through body composition. The study population consisted of 522 participants (264 women and 258 men) of the Longitudinal Aging Study Amsterdam (LASA), aged 65 years and over, and living in Amsterdam and its vicinity. BMD of the total hip was measured using dual-energy X-ray absorptiometry (DXA). Potential determinants of BMD were age, weight change since age 25 years, lifestyle factors, chronic diseases, medication use, and hormonal factors. Potential mediators between the possible determinants and BMD were two measures of body composition: fat mass (FM) and appendicular muscle mass (AMM). Multiple regression analyses including all potential determinants in one model without body composition identified age, weight change, walking activity, and sex hormone-binding globulin (SHBG) as independent determinants for total hip BMD in women. In men, current smoking, participation in sports, and parathyroid hormone (PTH) concentration were independently associated with total hip BMD. When total hip BMD was regressed on the potential determinants and each measure of body composition, it appeared that FM, and to a lesser extent, muscle mass (MM), were independently related to BMD. In women, adjustment for FM reduced the strength of the associations of weight change, walking activity, and SHBG with total hip BMD. Adjustments for MM did not influence the associations between the determinants and BMD. In men, neither FM nor MM appeared to play a mediating role between the determinants and BMD. It can be concluded that (1) FM and MM are strong independent determinants of total hip BMD and that (2) FM possibly plays a mediating role in the association of weight change, walking activity, and SHBG with total hip BMD in women.

Muscularity and the density of the fat-free mass in athletes

The purpose of this study was to use estimates of body composition from a four-component model to determine whether the density of the fat-free mass (D(FFM)) is affected by muscularity or musculoskeletal development in a heterogenous group of athletes and nonathletes. Measures of body density by hydrostatic weighing, body water by deuterium dilution, bone mineral by whole body dual-energy X-ray absorptiometry (DXA), total body skeletal muscle estimated from DXA, and musculoskeletal development as measured by the mesomorphy rating from the Heath-Carter anthropometric somatotype were obtained in 111 collegiate athletes (67 men and 44 women) and 61 nonathletes (24 men and 37 women). In the entire group, D(FFM) varied from 1.075 to 1.127 g/cm3 and was strongly related to the water and protein fractions of the fat-free mass (FFM; r = -0.96 and 0.89) and moderately related to the mineral fraction of the FFM (r = 0.65). Skeletal muscle (%FFM) varied from 40 to 68%, and mesomorphy varied from 1.6 to 9.6, but neither was significantly related to D(FFM) (r = 0.11 and -0.14) or to the difference between percent fat estimated from the four-component model and from densitometry (r = 0.09 and -0.16). We conclude that, in a heterogeneous group of young adult athletes and nonathletes, D(FFM) and the accuracy of estimates of body composition from body density using the Siri equation are not related to muscularity or musculoskeletal development. Athletes in selected sports may have systematic deviations in D(FFM) from the value of 1.1 g/cm3 assumed in the Siri equation, resulting in group mean errors in estimation of percent fat from densitometry of 2-5% body mass, but the cause of these deviations is complex and not simply a reflection of differences in muscularity or musculoskeletal development.

Lower limb skeletal muscle mass: development of dual-energy X-ray absorptiometry prediction model

Although magnetic resonance imaging (MRI) can accurately measure lower limb skeletal muscle (SM) mass, this method is complex and costly. A potential practical alternative is to estimate lower limb SM with dual-energy X-ray absorptiometry (DXA). The aim of the present study was to develop and validate DXA-SM prediction equations. Identical landmarks (i.e., inferior border of the ischial tuberosity) were selected for separating lower limb from trunk. Lower limb SM was measured by MRI, and lower limb fat-free soft tissue was measured by DXA. A total of 207 adults (104 men and 103 women) were evaluated [age 43 +/- 16 (SD) yr, body mass index (BMI) 24.6 +/- 3.7 kg/m(2)]. Strong correlations were observed between lower limb SM and lower limb fat-free soft tissue (R(2) = 0.89, P < 0.001); age and BMI were small but significant SM predictor variables. In the cross-validation sample, the differences between MRI-measured and DXA-predicted SM mass were small (-0.006 +/- 1.07 and -0.016 +/- 1.05 kg) for two different proposed prediction equations, one with fat-free soft tissue and the other with added age and BMI as predictor variables. DXA-measured lower limb fat-free soft tissue, along with other easily acquired measures, can be used to reliably predict lower limb skeletal muscle mass.

Measuring leg muscle and fat mass in humans: comparison of CT and dual-energy X-ray absorptiometry

Dual-energy X-ray absorptiometry (DEXA) is reported to be inferior to computed tomography (CT) to measure changes in appendicular soft tissue composition. We compared CT- and DEXA-measured thigh muscle and fat mass to evaluate the random and systematic discrepancies between these two methods. Thigh skeletal muscle area (single-slice CT) was suboptimally (r(2) = 0.74, P < 0.0001) related to DEXA-measured thigh fat-free mass (FFM). In contrast, thigh muscle and adipose tissue volumes (multislice CT) were highly related to DEXA-measured thigh FFM and fat (both r(2) = 0.96, P < 0.0001). DEXA-measured leg fat was significantly less than multislice-CT-measured leg adipose tissue volume, whereas multislice-CT-measured leg muscle mass was less (P < 0.0001) than DEXA-measured leg FFM. The systematic discrepancies between the two approaches were consistent with the 10-15% nonfat components of adipose tissue. In conclusion, CT and DEXA measures of appendicular soft tissue are highly related. Systematic differences between DEXA and CT likely relate to the underlying principles of the techniques.