70 research outputs found
Dual Energy X-Ray Absorptiometry Body Composition Reference Values from NHANES
In 2008 the National Center for Health Statistics released a dual energy x-ray absorptiometry (DXA) whole body dataset from the NHANES population-based sample acquired with modern fan beam scanners in 15 counties across the United States from 1999 through 2004. The NHANES dataset was partitioned by gender and ethnicity and DXA whole body measures of %fat, fat mass/height2, lean mass/height2, appendicular lean mass/height2, %fat trunk/%fat legs ratio, trunk/limb fat mass ratio of fat, bone mineral content (BMC) and bone mineral density (BMD) were analyzed to provide reference values for subjects 8 to 85 years old. DXA reference values for adults were normalized to age; reference values for children included total and sub-total whole body results and were normalized to age, height, or lean mass. We developed an obesity classification scheme by using estabbody mass index (BMI) classification thresholds and prevalences in young adults to generate matching classification thresholds for Fat Mass Index (FMI; fat mass/height2). These reference values should be helpful in the evaluation of a variety of adult and childhood abnormalities involving fat, lean, and bone, for establishing entry criteria into clinical trials, and for other medical, research, and epidemiological uses
Relationship between age and elite marathon race time in world single age records from 5 to 93 years
Features, Causes and Consequences of Splanchnic Sequestration of Amino Acid in Old Rats
RATIONALE: In elderly subjects, splanchnic extraction of amino acids (AA) increases during meals in a process known as splanchnic sequestration of amino acids (SSAA). This process potentially contributes to the age-related progressive decline in muscle mass via reduced peripheral availability of dietary AA. SSAA mechanisms are unknown but may involve an increased net utilization of ingested AA in the splanchnic area. OBJECTIVES: Using stable isotope methodology in fed adult and old rats to provide insight into age-related SSAA using three hypotheses: 1) an increase in protein synthesis in the gut and/or the liver, 2) an increase in AA oxidation related to an increased ureagenesis, and 3) Kupffer cell (KC) activation consequently to age-related low-grade inflammation. FINDINGS: Splanchnic extraction of Leu (SPELeu) was doubled in old rats compared to adult rats and was not changed after KC inactivation. No age-related effects on gut and liver protein synthesis were observed, but urea synthesis was lower in old rats and negatively correlated to liver Arg utilization. Net whole-body protein synthesis and arterial AA levels were lower in old rats and correlated negatively with SPELeu. CONCLUSION: SSAA is not the consequence of age-related alterations in ureagenesis, gut or liver protein synthesis or of KC activity. However, SSAA may be related to reduced net whole-body protein synthesis and consequently to the reduced lean body mass that occurs during aging
Reduced Satellite Cell Numbers and Myogenic Capacity in Aging Can Be Alleviated by Endurance Exercise
Background: Muscle regeneration depends on satellite cells, myogenic stem cells that reside on the myofiber surface. Reduced numbers and/or decreased myogenic aptitude of these cells may impede proper maintenance and contribute to the age-associated decline in muscle mass and repair capacity. Endurance exercise was shown to improve muscle performance; however, the direct impact on satellite cells in aging was not yet thoroughly determined. Here, we focused on characterizing the effect of moderate-intensity endurance exercise on satellite cell, as possible means to attenuate adverse effects of aging. Young and old rats of both genders underwent 13 weeks of treadmill-running or remained sedentary. Methodology: Gastrocnemius muscles were assessed for the effect of age, gender and exercise on satellite-cell numbers and myogenic capacity. Satellite cells were identified in freshly isolated myofibers based on Pax7 immunostaining (i.e., exvivo). The capacity of individual myofiber-associated cells to produce myogenic progeny was determined in clonal assays (in-vitro). We show an age-associated decrease in satellite-cell numbers and in the percent of myogenic clones in old sedentary rats. Upon exercise, there was an increase in myofibers that contain higher numbers of satellite cells in both young and old rats, and an increase in the percent of myogenic clones derived from old rats. Changes at the satellite cell level in old rats were accompanied with positive effects on the lean-to-fat Gast muscle composition and on spontaneous locomotion levels. The significance of these data is that they suggest that the endurance exercise-mediated boost in bot
Thigh muscle volume in relation to age, sex and femur volume
Secular changes and intra-individual differences
in body shape and size can confound crosssectional
studies of muscle ageing. Normalising muscle
mass to height squared is often suggested as a solution for
this. We hypothesised that normalisation of muscle volume
to femur volumemay be a better way of determining
the extent of muscle lost with ageing (sarcopenia). Thigh
and femur muscle volumes were measured from serial
magnetic resonance imaging sections in 20 recreationally
active young men (mean age 22.4 years), 25 older men
(72.3 years), 18 young women (22.1 years) and 28 older
women (72.0 years). There were no age-related differences
in femur volume. The relationship between thigh
muscle volume and femur volume (R2=0.76; exponent of
1.12; P<0.01) was stronger than that with height
(R2=0.49; exponent of 3.86; P<0.01) in young participants.
For young subjects, the mean muscle/bone ratios
were 16.0 and 14.6 for men and women, respectively. For
older men and women, the mean ratios were 11.6 and
11.5, respectively. The Z score for the thigh muscle/bone
volume ratio relative to young subjects was −2.2±0.7 for
older men and −1.4±0.8 for older women. The extent of
sarcopenia judged by the muscle/bone ratio was approximately
twice that determined when normalising to
height squared. These data suggest that the muscle/bone
ratio captures the intra-individual loss of muscle mass
during ageing, and that the age-related loss of muscle
mass may be underestimated when normalised to height
squared. The quadriceps seems relatively more affected
by ageing than other thigh muscles
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