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Military Performance Division, United States Army Research Institute of Environmental Medicine, Natick, Massachusetts 01760
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ABSTRACT |
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 TOP
 ABSTRACT
 INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
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This study evaluated the arm,
trunk, and leg for fat mass, lean soft tissue mass, and bone mineral
content (BMC) assessed via dual-energy X-ray absorptiometry in a group
of age-matched (~29 yr) men (n = 57) and women
(n = 63) and determined their relationship to
insulin-like growth factor I (IGF-I) and leptin. After analysis of
covariance adjustment to control for differences in body mass between
genders, the differences that persisted (P 
0.05) were for
lean soft tissue mass of the arm (men: 7.1 kg vs. women: 6.4 kg) and
fat mass of the leg (men: 5.3 kg vs. women: 6.8 kg). Men and women had
similar (P 
0.05) values for fat mass of the arms and
trunk and lean soft tissue mass of the legs and trunk. Serum IGF-I and
insulin-like growth factor binding protein-3 correlated (P 0.05) with all measures of BMC (r values ranged from 0.31 to 0.39) and some measures of lean soft tissue mass for women
(r = 0.30) but not men. Leptin correlated (P 0.05) similarly for measures of fat mass for both genders
(r values ranging from 0.74 to 0.85) and for lean soft
tissue mass of the trunk (r = 0.40) and total body
(r = 0.32) for men and for the arms in women
(r = 0.56). These data demonstrate that 1)
the main phenotypic gender differences in body composition are that men have more of their muscle mass in their arms and women have more of
their fat mass in their legs and 2) gender differences exist in the relationship between somatotrophic hormones and lean soft tissue mass.
appendicular skeletal muscle; adiposity; somatotrophic hormones; military personnel; insulin-like growth factor I
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INTRODUCTION |
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TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
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DUAL-ENERGY X-RAY
ABSORPTIOMETRY (DXA) has become widely accepted and used as a
valid and reliable method to assess regional body composition (7,
9, 18, 22, 23). The fact that DXA can yield accurate
estimates of regional as well as overall body composition offers
advantages over more traditional means of body composition measurement
in that 1) the health risks associated with fat mass are
more related to regional placement rather than overall adiposity,
2) the plasticity of tissue mass is known to be influenced
by anatomic location, and 3) DXA estimates of regional tissue mass offer more resolution than either skinfolds or
circumferences (7, 18). Even though DXA has been an
accepted means for assessing body composition for some time, a review
of the literature reveals a surprising lack of normative data for
samples of young men and women. Gallagher et al. (9) have
provided one of the few gender comparisons of DXA values for skeletal
muscle mass of the arms and legs for a population averaging over 40 yr
of age. Because a reduction in strength and muscle mass can
begin around age 30 yr, a need also exists for DXA values on younger
(i.e., 30 yr) populations.
Men and women are known to differ in body strength, particularly of the upper body. A partial explanation for the strength disparity between genders is that men have more of their muscle mass in the upper body. Although this is a reasonable hypothesis, the data supporting this contention come mainly from magnetic resonance imaging (MRI) and computed tomography (CT), with a paucity of data available from DXA technology. For example, using MRI, Janssen et al. (11) reported that men had 42.9 and 54.9% of their skeletal muscle mass distributed to their upper and lower body, whereas women had 39.7 and 57.7% of their skeletal muscle mass distributed to their upper and lower body, respectivly. Furthermore, using CT, Miller et al. (19) reported that the cross-sectional areas of women's biceps brachi, elbow flexors, vastus lateralis, and knee extensors were 55, 59, 70, and 75% those of men, respectively. Compared with MRI and CT, DXA allows for simultaneous measures of total body and regional content of fat mass, lean mass, and bone mineral content. In addition to representative data on regional muscle mass, it would also seem prudent to possess representative data on regional fat mass and bone mineral content (BMC), because obesity, osteoporosis, and sarcopenia are currently major public health concerns.
Circulating endogenous hormones are thought to mediate the outcomes of physical activity by modulating tissue remodeling (24, 27, 30). Two candidate hormonal biomarkers that have received attention on the basis of their somatotrophic actions are insulin-like growth factor-I (IGF-I) and leptin. For example, IGF-I is known to exert robust mitogenic, myogenic, and anabolic tissue actions in both an endocrine and an autocrine and/or paracrine fashion. IGF-I action is modulated by a family of binding proteins that can either augment or inhibit its physiological action. In fact, acute resistance exercise has been recently shown to alter specific IGF binding proteins [i.e., insulin-like growth factor binding protein (IGFBP)-2 and the acid-labile subunit] influencing IGF-I action (27).
The influences of the IGF-I system on muscle and bone are particularly well acknowledged. Sun et al. (34) observed that the IGF-I gene marker was associated with static measures of fat and fat-free mass and was strongly linked to changes in fat-free mass in response to exercise training. In addition, Snow et al. (32) reported that both IGF-I and its ratio to the main IGF binding protein, IGFBP-3, are predictive of lean and bone mass in female gymnasts. It remains to be determined to what extent systemic measures of the IGF-I system are related to regional measures of body composition and whether gender differences exist in these relationships.
The adipocyte-derived hormone leptin is another protein that has gained recent attention and is known to be highly correlated with adiposity (21, 37). Leptin has been shown to be more associated with subcutaneous fat than omental fat (10), but little information is available concerning associations between leptin and regional (i.e., arm, leg, and trunk) fat mass. Because fat tissue mass is known to possess different sensitivities to endocrine stimuli depending on anatomic location (4), so too might leptin have dissimilar associations with fat mass depending on regional location. Leptin has also been reported to influence fat-free mass. Fernandez-Real et al. (6) found that for men, but not women, fat-free mass explained a significant amount of the variance for leptin. Also, Bennett et. al. (2) reported that leptin was influenced by regional distribution of adipose tissue. Although tissue mass is known to exhibit a great deal of plasticity due to exercise training or metabolic and/or pharmacalogical manipulations, more detail is required to delineate the precise systemic and local hormonal influences. Further examination of gender differences in somatotrophic hormonal influences on body morphology may help to define normal vs. pathological associations across the life span.
To our knowledge, no previous reports have examined the relationship between circulating components of the IGF-I system and leptin on regional distribution of fat tissue, lean soft tissue, and BMC. We hypothesized that IGF-I would be more closely related to lean soft tissue mass and BMC, whereas leptin would be more closely related to fat mass. Additionally, we anticipated because men and women exhibited a differential distribution of their tissue mass, so too would they possess differential relationships between circulating hormones and tissue mass. The purposes of this investigation, therefore, were 1) to compare the regional distribution of DXA-assessed fat tissue mass, lean soft tissue mass, and BMC in a group of age-matched young adults, before and after statistical control for differences in body size, and 2) to evaluate the relationship between circulating measures of the IGF-I system (i.e., total IGF-I and IGFBP-2, -3, and -6) and leptin to regional measures of body composition in this same sample of men and women.
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METHODS |
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TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
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Subjects. Participants for this study were 57 men (age 28.8 ± 0.7 yr, weight 83.4 ± 13.8 kg, height 177.0 ± 7.0 cm, %body fat 18.2 ± 5.8, body mass index 26.6 ± 4.0 m2/kg) and 63 women (age 29.2 ± 1.0 yr, weight 66.3 ± 9.1 kg, height 167.0 ± 6.0 cm, %body fat 26.3 ± 4.8, body mass index 23.7 ± 3.1 m2/kg) who were participating in a longitudinal study tracking bone mineral density changes. All subjects were graduates of the United States Military Academy at West Point who had read and signed an institutionally approved consent form. Because the subjects were all members of the same graduating class (West Point class of 1994), our study population was age matched, thereby eliminating any potential confounding effect due to age. This study was approved by the Human Use Review Committee at the United States Army Research Institute of Environmental Medicine (Natick, MA) and by the Human Subjects Research Review Board Office of the Medical Research and Materiel Command, which falls under the office of the Army Surgeon General. As a part of the study, all subjects were given a comprehensive medical screening by a physician to identify and eliminate potential confounding endocrine, orthopedic, or other pathologies that would adversely impact the study measures. The subjects had their physical screening, DXA scan, and blood drawn all during the same day.
DXA. Total body estimates of percentage of fat, bone mineral density, and bodily content of bone, fat, and nonbone lean tissue were determined by using manufacturer-supplied algorithms (Total Body Analysis, version 3.6, Lunar, Madison, WI). Precision of this measurement is better than ±0.5% body fat. For this procedure, the volunteer dressed in shorts and tee shirt and lay face up on a DXA scanner table. The body was carefully positioned so that it was laterally centered on the table with the hands palm downward. Velcro straps were used to keep the knees together and support the feet so that they tilted 45° from the vertical. Scanning was in 1-cm slices from head to toe by using the 20-min scanning speed. Regional measurements (arm, leg, and trunk) were determined on the basis of bony landmarks via manual analysis by the same trained and experienced technician. Vertical boundaries separated the arms from the body at the shoulder, and angled boundaries separated the legs from the trunk. Precision of the measurement calculated as coefficient of variations for replicate scans in our laboratory was 1.5, 0.8, and 1.1% for the arms, legs, and trunk, respectively.
Hormonal analyses.
After an overnight fast, blood was obtained via venipuncture in the
morning (between 0700 and 1000). Subjects were instructed not
to exercise or engage in strenuous physical activity before reporting
to the laboratory. After collection, blood was allowed to clot at room
temperature and then centrifuged for 30 min at 800 g at
4°C. After centrifugation, serum was aliquoted into a preservative
tube, flash frozen in liquid nitrogen, and stored at 
80°C until
later analysis. All IGF-I system assays were performed with
immunoassays (Diagnostic Systems Laboratories, Webster, TX) on a Cobra
gamma counter (Packard Instruments, Downers Grove, IL). All samples for
a particular analyte were run in the same assay batch to eliminate
interassay variance. Total IGF-I, IGFBP-3, and leptin concentrations
were determined by using two-site immunoradiometric assays. The
sensitivity of these assays by using the B0 ± 2 SD was 2.06, 0.5, and 0.1 ng/ml for total IGF-I, IGFBP-3, and leptin, respectively. IGFBP-2 and IGFBP-6 concentrations were
determined by using radioimmunoassays. The sensitivity of these assays
using the B0 ± 2 SD was 0.5 and 1.1 ng/ml for IGFBP-2
and IGFBP-6, respectively. The internal intra-assay variances obtained
from replicate tubes of low, medium, and high concentrations supplied
by the company were <6% for all immunoassays. Additionally, for all
assays, control standards supplied by the company of low and high
concentrations were run in all assays and found to be within specified limits.
Statistics.
Statistical analysis was conducted with the Statistical Programs for
the Social Sciences (SPSS, Chicago, IL). Descriptive statistics were
calculated for all measures. Homogeneity of variance and normality of
distribution were determined on all data by examining the skewness and
kurtosis values. Absolute tissue mass and proportions of tissue totals
were determined for arm, trunk, and leg fat, soft tissue mass, and BMC.
Subsequently, all gender comparisons were performed with an independent
Student's t-test. Additionally, to control for differences
in body mass between men and women, analysis of covariance (ANCOVA)
assessed differences in regional tissue mass after covarying for total
tissue mass. The ANCOVA involved deriving a pair of male and female
regression-based equations of regional tissue mass as a function of
total tissue mass. Homogeneity of variance was confirmed
(P > 0.05), as was the linearity between the regional
tissue mass of interest and total tissue mass. Pearson product-moment
correlation coefficients evaluated the relationship between regional
tissue mass and concentrations of IGF-I, IGFBP-2, IGFBP-3, IGFBP-6, and
leptin. An 
level of 0.05 was used for statistical significance.
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RESULTS |
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TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
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Table 1 shows the DXA-assessed total
and regional values for soft tissue, percentage of fat, fat tissue,
lean soft tissue, and BMC for men and women. As expected, men
had significantly (P 0.05) different values compared with
women on all measures, with the exception of trunk fat tissue. Compared
with men, women had 71, 84, and 78% of total soft tissue, 56, 71, and
72% of the absolute lean soft tissue mass, 125, 137, and 110% of the
absolute fat mass, and 80, 77, and 82% of the absolute BMC for the
arms, legs, and trunk, respectively.
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To correct for differences in body size, ANCOVA was subsequently used
to control for the influence of the total amount of the specific
tissue. The adjusted means from the ANCOVA are shown in Table
2. After ANCOVA adjustments, women had
similar (P 0.05) total soft tissue values as men for arms
(98% of the male value), trunk (99% of the male value), and legs
(103% of the male value). Women had lower lean soft tissue values for
arms (91% of the male value) but had similar values for trunk (102%
of the male value) and legs (101% of the male value). Women had
similar values as men for fat tissue for arms (110% of the male value) and trunk (103% of the male value) but higher values for legs (129%
of the male value). Women had lower BMC values for the arms (83% of
the male value) and legs (97% of the male value) but had higher values
for trunk (112% of the male value).
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Figure 1 shows a gender comparison for
the relative distribution of regional tissue mass as a percentage of
total tissue mass before ANCOVA adjustment. In Fig. 1A, men
had more (P 0.05) of their total soft tissue mass
distributed to their arms (15.1 vs. 13.4%), similar amounts of total
tissue distributed to their trunk (49.1 vs. 49.0%), and less in their
legs (35.8 vs. 37.6%) than women. In Fig. 1C, men had more
lean soft tissue mass distributed in their arms (15.1 vs. 12.2%) and
less in their trunk (48.8 vs. 50.8%) and legs (36.1 vs. 37.0%) than
women. In Fig. 1B, men had less of their total fat tissue
mass distributed to their arms (15.0 vs. 16.1%) and legs (34.5 vs.
39.3%) and more to their trunk (50.5 vs. 44.6%) than women. In Fig.
1D, men had more of their BMC distributed in their arms
(17.7 vs. 15.3%) and legs (44.7 vs. 43.5%) but less in their trunk
(37.6 vs. 41.2%) than women.
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Table 3 shows the circulating IGF-I
system and leptin concentrations for men and women. Men had lower
concentrations of IGF-I, IGFBP-3, and leptin and higher concentrations
of IGFBP-2 and IGFBP-6, than women.
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Table 4 shows the correlations between
IGF-I, IGFBP-3, leptin, and regional measures of body composition
for men and women. In women, IGF-I correlated significantly with total
soft tissue mass in the legs (r = 0.32), overall total
soft tissue mass (r = 0.27), total lean soft tissue
mass (r = 0.32), lean soft tissue in the arms
(r = 0.30) and legs (r = 0.35), total
BMC (r = 0.39), and BMC in the arms (r = 0.36), legs (r = 0.33), and trunk (r = 0.39). In contrast, IGF-I did not correlate with any of the DXA
measures in men. IGFBP-3 correlated significantly in women for total
lean soft tissue (r = 0.31), lean soft tissue in the trunk (r = 0.30), and total BMC (r = 0.38), as well as BMC in the arms (r = 0.31), legs
(r = 0.34), and trunk (r = 0.37). In contrast to the women, but similar to the IGF-I concentrations, IGFBP-3 did not correlate with any of the DXA measures in men. Furthermore, IGFBP-2, IGFBP-6, and the IGF-I/IGFBP-3 ratio were not
significantly correlated with any measure of regional body composition
for either men or women (data not shown).
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Leptin correlated significantly (r = 0.58-0.85) for all regional measures of total soft tissue, region percent fat, and fat mass for both men and women. Additionally, leptin correlated significantly in men for total lean soft tissue (r = 0.32) and lean soft tissue in the trunk (r = 0.40). Leptin correlated significantly in women for lean soft tissue in the arms (r = 0.56) and BMC in the trunk (r = 0.34).
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DISCUSSION |
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TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
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This study has provided a gender comparison for DXA-assessed regional fat, lean soft tissue, and BMC in the arms, trunk, and legs in a sample of age-matched (29-yr-old) men and women both before and after statistical control for differences in body mass. These important design elements offer advantages over most previous studies where between-gender comparisons of body composition did not adequately control for age or body mass. Additionally, gender differences were examined between the relationship of these regional body composition measures and circulating concentrations of the IGF-I system and leptin.
On an absolute basis, men had greater values for lean soft tissue mass and BMC in all regions and less fat mass in all regions, with the exception of the trunk. However, after statistical control for total regional tissue mass, gender differences that persisted were for lean soft tissue mass of the arm and fat mass of the leg. Of note, after ANCOVA adjustment, men and women had similar values for fat mass of the arms and trunk and lean soft tissue mass of the legs and trunk. These results demonstrate that, independent of overall body size, the well-known differences in muscularity between men and women are primarily attributed to men having a greater relative amount of lean soft tissue mass in their arms and to women having a greater relative amount of fat tissue in their legs. A prominent gender difference was also observed for the relationship between circulating IGF-I and IGFBP-3 and body composition, because significant correlations were found for lean soft tissue mass and BMC in women but not men.
Regional lean soft tissue mass. By reporting all in vivo regional measures (i.e., fat, lean soft tissue, and BMC) available from the DXA scan and by testing a homogeneous age group, our data extend the results of Gallagher et al. (9) and Janssen et al. (11), who evaluated only appendicular skeletal muscle mass in men and women. Gallagher et al. reported that leg-to-arm ratios of appendicular skeletal muscle mass were ~2.95 for 136 men and ~3.5 for 148 women averaging >40 yr of age. The leg-to-arm ratios of appendicular skeletal muscle mass for the men and women in this study were 2.42 and 3.07, respectively. The lower ratios for the younger subjects are in agreement with the prevailing theory that upper extremity muscle mass decreases to a relatively greater extent than lower extremity muscle mass (8).
As expected, on an absolute basis, men had more lean soft tissue mass in all regions than did women. However, when covaried for total lean soft tissue mass, the only gender difference remaining was for lean soft tissue mass of the arms (women had 90% of the male value). These findings differ somewhat from the data of Gallagher et al. (9), who reported that, in a sample of racially mixed subjects >40 yr of age, men had greater skeletal muscle mass of both the arms and legs, independent from height, age, and weight. Nonetheless, our data show that, for an age-matched group of 29-yr-old men and women, the most striking gender difference for lean soft tissue mass is for the arms. However, it is important to note that, with heavy resistance training, women can show impressive hypertrophic gains of 20% for the arm musculature (13).Regional fat mass. The men and women in this study differed with respect to the relative proportionality of regional fat deposition. More divergence among arm, trunk, and leg regional adiposity was observed for women (a range of 27-34%) than men (a range of 18-19%), with women exhibiting an accentuated relative deposition toward the arm region. When expressed as a percentage of total fat mass, men had a greater percent deposited in the trunk than women (51 vs. 45%, respectively), whereas women had a greater percent deposited in their legs (39 vs. 35%, respectively) and arms (16 vs. 15%, respectively) than men.
The similarity in relative adiposity for the arm (19.2%), leg (18.1%), and trunk (19.7) regions for the men in this study differs from our previous reports (22, 23) on active duty military men who regularly engage in physical training, particularly for a group of highly trained Ranger cadets who demonstrated a "fit-fat" distribution [i.e., fat storage away from the abdomen (14.3%) and arm (12.1%) and toward the leg (16.5%) region] (22). The fact that, of the population of the present study, 52% of the subjects were no longer in the military and presumably "less active" and were approaching their third decade of life could partially explain the propensity for the fat storage observed in the arm and trunk region. Using regional DXA analysis, Stewart and Hannan (35) also demonstrated that lean male athletes had a different fat distribution compared with nonexercising controls. Compared with controls, whole-body-exercising athletes had proportionally less fat in their torso but more fat in their arm and leg regions. These findings support the contention that regular exercise training can serve to regulate regional deposition of fat mass. The mechanism behind this phenomenon is presently unknown but could be related to exercise-mediated changes in adipose biology for regional lipoprotein lipase activity and/or responsiveness to lipolytic stimuli. In contrast to the men, the women in this study showed more heterogeneity in the relative adiposity for the arm (34.9%), leg (30.1%), and trunk (27.1%) regions. The greater relative proportion of adiposity in the arm is in agreement with the cross-sectional data of Madsen et al. (17), who also reported that arm adiposity increases to a greater extent than the other regions with age in women. As in men, regular exercise training has also been shown to alter the distribution of fat in women. In fact, after 6 mo of periodized (i.e., systematic manipulation of training volume and intensity over time) physical training conducted 5 days/wk, women changed their relative adiposity for their arm, leg, and trunk, respectively, from 40, 34.4, and 33.8% to 31.3, 33.4, and 30.8% (23). Another contrast to men is that, on an absolute basis, women possessed more fat tissue in the leg region, whereas men had more in the trunk region. After statistical control for overall fat mass, the only significant gender difference was in the leg region. Leg fat deposition in women has been shown to have clinical implications, because it is a useful marker for hyperinsulinemia and lipid disorders in women (36). Femoral adipose tissue is known to be quite resistant to mobilization, and preferential accumulation of adipose tissue in the femoral region of women could be due to enhanced lipoprotein lipase activity favoring fat cell triglyceride deposition (4, 22).Relationship between regional body composition and IGF-I and leptin. Tissue remodeling is under the homeostatic control of hormonal influences that can act via both systemic and local mechanisms (26, 28, 30, 39). This study has explored the relationship between circulating concentrations of the IGF-I system and leptin and regional body composition in a sample of age-matched men and women. Interestingly, serum IGF-I and IGFBP-3 correlated with all regions of BMC and arm, leg, and whole body lean soft tissue mass for women but not men. Although IGF-I concentrations have been reported to be low in men with idiopathic osteoporosis (14) and in hip and spinal fracture patients (33), the previous literature on relationships between circulating IGF-I and BMD are mixed. Boonen et al. (3) published the first study demonstrating a consistent positive relationship between serum IGF-I and BMD in a sample of 245 community-dwelling women over age 70 yr. Similar to the results of our study, Barrett-Connor and Goodman-Gruen (1) and Langlois et al. (15) reported that IGF-I was correlated with the spine and hip BMD in women but not in men. Rudman et al. (30) also failed to observe a significant relationship between IGF-I and BMD in healthy middle-aged men. In contrast, Janssen et al. (12) found that total and free IGF-I weakly correlated with lumbar spine BMD in men not women. Finally, Lloyd et al. (16) and Collins et al. (5) failed to observe any significant correlation between IGF-I and BMD in women aged 40-68 yr. Thus it appears that the relationship between circulating IGF-I and BMD may be tenuous. On the other hand, it may be that skeletal IGF-I operates more dramatically as an osteotropic agent in an autocrine and/or paracrine fashion, which would not be detected by only measuring it in the circulation (19, 28). Indeed, serum and skeletal IGF-I concentrations show little agreement when directly compared (31).
The regulatory complexity of the IGF-I system is further evidenced through its array of binding proteins (27, 33, 38). Sugimoto et al. (33) demonstrated that IGFBP-3 and -2 correlated positively and negatively, respectively with BMD in women. For the present study, only IGFBP-3, not IGFBP-2 or -6, or the IGF-I/IGFBP-3 ratio correlated with measures of BMC and lean soft tissue mass in women, and these relationships tracked with IGF-I. This seems reasonable, because over 75% of IGF-I exists in a ternary complex bound to IGFBP-3 and the acid-labile subunit. Any explanation for the apparent gender difference in IGF-I relationships observed in this study and that of Barret-Connor and and Goodman-Gruen (1) is only speculative, but it could include the involvement of a differential interaction among other systemic and local endocrine factors and bone turnover between men and women. The correlations between leptin and body fat ranged from 0.74 to 0.85, which are consistent with previous literature. In general, the correlations were higher for men. Leptin correlated similarly with fat mass for arm, leg, and trunk regions in men and women, respectively. These findings differ from those of Taylor and Goulding (37), who found that trunk fat explained more of the variance in circulating leptin concentrations than leg fat in women aged 40-79 yr. The disparate findings between the studies could be explained by the women being pre- vs. postmenopausal. Our findings of similar correlations between leptin and DXA-assessed regional fat mass and the findings of Hube et al. (10) and Montague et al. (21) that leptin expression is higher in subcutaneous than omental fat may suggest that the type of fat, not the anatomic location of fat per se, more strongly influences leptin concentrations. Another intriguing finding in the present study was that leptin significantly correlated with total lean soft tissue mass and trunk soft tissue mass in men and with lean soft tissue lean mass of the arms on women. Fernandez-Real et al. (6) also reported a gender difference with fat-free mass explaining a significant amount of the variance in circulating leptin for men but not women. For the regional associations, the fact that leptin correlated with the lean regional soft tissue mass with the greatest relative amount of adiposity for men and women, respectively, makes it interesting to speculate that elevated intramuscular fat in these areas contributed to both a greater relative amount of DXA-assessed adiposity and a stronger correlation with leptin. In conclusion, our study has demonstrated that, after controlling for age and body size, the main phenotypic gender differences in body composition are that men have more of their muscle mass in their arms and women have more of their fat mass in their legs. Additionally, distinct gender differences exist for somatotrophic hormonal influences and total body lean soft tissue mass, with IGF-I and IGFBP-3 correlating in women and leptin correlating in men. Although this gender difference currently remains unexplained, further studies aimed at uncovering the mechanisms involved could be clinically important by contributing to our knowledge of hormonal influences on body composition throughout the life span.| |
ACKNOWLEDGEMENTS |
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We gratefully acknowledge the participation of members of the West Point class of 1994 who volunteered for this study. We also are indebted to Michele Mayo, Doreen Hafeman, and Michele Ward, who assisted in data collection and analysis. We thank John F. Patton, PhD, and Shari Hallas for for insightful comments and assistance in manuscript preparation.
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FOOTNOTES |
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Address for reprint requests and other correspondence: B. C. Nindl, Military Performance Division, United States Army Research Institute of Environmental Medicine, Natick, MA 01760 (E-mail: Bradley.Nindl{at}NA.AMEDD.Army.Mil).
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
First published December 21, 2001;10.1152/japplphysiol.00892.2001
Received 27 August 2001; accepted in final form 7 December 2001.
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TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
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