title: Body composition changes by DXA, BIA and skinfolds during exercise training in women.
abstract: OBJECTIVE
  Few studies have examined responsiveness of bioimpedance (BIA) to detect changes over time in body composition using a longitudinal design. Accuracy of BIA and skinfold thickness in estimating body composition among 39-64 year-old women was investigated using dual-energy X-ray absorptiometry (DXA) as a criterion method both cross-sectionally and during a training intervention.
  
  
  METHODS
  97 women had percentage of fat assessed using DXA, skinfolds and eight-polar BIA using multi-frequency current. Fat mass and lean mass were estimated by DXA and BIA. Measurements were performed before and after the 21-week training intervention.
  
  
  RESULTS
  At baseline relative to DXA, BIA under predicted percentage of fat (-6.50 %) and fat mass (-3.42 kg) and overestimated lean mass (3.18 kg) considerably. Also skinfold measurement under predicted percentage of fat compared to DXA, but the difference was smaller (-1.69 % units). Skinfold measurement overestimated percentage of fat at low values and underestimated at high values (r (2) = 0.535). A significant bias was detected between DXA and BIA's estimate of change in percentage of fat, fat mass and lean mass. Compared to DXA, BIA and skinfolds underestimated the training-induced positive changes in body composition.
  
  
  CONCLUSIONS
  BIA and skinfold methods compared to DXA are not interchangeable to quantify the percentage of fat, fat mass and lean mass at the cross-sectional design in middle-aged women. Moreover, exercise training-induced small changes in body composition cannot be detected with BIA or skinfold method, even though DXA was able to measure statistically significant within-group changes in body composition after training.
authors.affiliation: Department of Biology of Physical Activity, University of Jyväskylä, P.O. Box 35 (VIV), 40014 Jyväskylä, Finland. elina.sillanpaa@jyu.fi
authors.forename: Elina
authors.initials: E
authors.lastname: Sillanpää
authors.forename: Arja
authors.initials: A
authors.lastname: Häkkinen
authors.forename: Keijo
authors.initials: K
authors.lastname: Häkkinen
mesh_terms: D015502:Absorptiometry, Photon / Q000379:methods; D000328:Adult; D001823:Body Composition / Q000502:physiology*; D015992:Body Mass Index; D003430:Cross-Sectional Studies; D004493:Education / Q000379:methods; D017097:Electric Impedance; D015444:Exercise / Q000502:physiology*; D005223:Fats / Q000378:metabolism; D005260:Female; D006801:Humans; D008875:Middle Aged; D012885:Skinfold Thickness
chemical_list: D005223:Fats