Abdominal obesity is an increasing problem in adolescents, often persisting into adulthood. Reliable assessment has been restricted to techniques limited by relatively high radiation doses or cost.
To investigate the reliability of several abdominal regions using dual-energy X-ray absorptiometry (DXA), and to assess the construct validity of these methods against metabolic profile.
Inter- and intra-rater precision of two assessors were examined, for fat mass analysis in six different abdominal regions using DXA in overweight/obese and normal weight adolescents. Construct validity was examined in overweight/obese individuals.
All methods had acceptable intra- and inter-rater reliability. Region 1 was most precise in overweight/obese individuals, while Region 6 was most precise in normal weight individuals. In all regions, assessments were less precise in overweight/obese individuals. All regions were equally predictive of insulin outcomes.
Abdominal adiposity can be reliably assessed in adolescents using DXA, and the most precisely assessed regions were identified. All regions predicted insulin outcomes.
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"For estimation of the central (truncal) fat, the trunk region (which includes the pelvis) was delineated by a single assessor using standard manufacturer analysis guidelines. The assessor (JB) has shown good inter-rater reliability with a colleague . Lumbar spine (L2-L4), BMD and BMC were also determined. "
[Show abstract][Hide abstract] ABSTRACT: Objective
Children treated with stimulant medication for attention deficit hyperactivity disorder (ADHD) often lose weight. It is important to understand the implications of this during growth. This prospective study was designed to quantify the changes in body composition and markers of bone metabolism on starting treatment.
34 children (29 boys) aged 4.7 to 9.1 years newly diagnosed with ADHD were treated with dexamphetamine or methylphenidate, titrating the dose to optimise the therapeutic response. Medication was continued for as long as clinically indicated. Body composition and bone density (dual-energy X-ray absorptiometry) were measured at baseline, 6 months and 3 years; changes were analysed in Z-scores based on data from 241 healthy, local children. Markers of bone turnover were measured at baseline, 3 months and 3 years.
Fat loss of 1.4±0.96kg (total fat 5.7±3.6 to 4.3±3.1kg, p<0.001) occurred in the first 6 months. There were significant reductions over 3 years in the sex and height corrected Z-scores for lean tissue, bone mineral content, bone mineral density and ratio of central to total fat (−0.84±0.86, p=0.003; -0.55±0.31, p<0.0001; -0.41±0.28, p<0.0001 and −0.55±0.62, p=0.006 respectively). Propeptide of type I collagen indicated a significant reduction in bone turnover after 3 months (564±202 to 458±96ng/ml, p=0.019), which was fully recovered after 3 years (619±276ng/ml).
Stimulant medication was associated with early fat loss and reduced bone turnover. Lean tissue including bone increased more slowly over 3 years of continuous treatment than would be expected for growth in height. There was long-term improvement in the proportion of central fat for height. This study shows that relatively minor reductions in weight on stimulant medication can be associated with long-term changes in body composition. Further study is required to determine the effects of these changes on adult health.
Full-text · Article · Dec 2012 · International Journal of Pediatric Endocrinology
"Indeed, these techniques generally overestimate FFM in obese adolescents (Lazzer et al. 2003) and cannot be used to compare relative muscle strength between obese and nonobese young people. Dualenergy X-ray absorptiometry (DXA) would be more appropriate to measure total body and regional soft tissue composition as this technique was found to be highly precise and reproducible in nonobese and obese young people (Figueroa- Colon et al. 1998; Bridge et al. 2011; Tsang et al. 2009). However, to the best of our knowledge, no study has used DXA measures of body dimensions to evaluate relative KE strength in obese and nonobese adolescents. "
[Show abstract][Hide abstract] ABSTRACT: 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.
Full-text · Article · Mar 2012 · Applied Physiology Nutrition and Metabolism
[Show abstract][Hide abstract] ABSTRACT: Aim. To examine the efficacy of a six-month Kung Fu (KF) program on physical fitness in overweight/obese adolescents. Methods. Subjects were randomly assigned to the KF or sham exercise (Tai Chi, TC) control group. Physical measurements in cardiovascular fitness and muscle fitness occurred at baseline and after 6 months of training thrice weekly. Results. Twenty subjects were recruited. One subject was lost to follow-up, although overall compliance to the training sessions was %. At follow-up, the cohort improved in absolute upper (
) and lower () body strength, and upper body muscle endurance (), without group differences. KF training resulted in significantly greater improvements in submaximal cardiovascular fitness (), lower body muscle endurance (; significant 95% CI: 0.37–2.49), and upper body muscle velocity () relative to TC training. Conclusions. This short-term KF program improved submaximal cardiovascular fitness, lower body muscle endurance, and muscle velocity, in overweight/obese adolescents with very low baseline fitness.
Full-text · Article · Jun 2010 · Journal of obesity