Body fat measurement in adolescent athletes: multicompartment molecular model comparison

Objective: To assess the accuracy of air displacement plethysmography (ADP) and dual energy X-ray absorptiometry (DXA) per cent body fat (%BF) estimations in comparison with a reference five-compartment (5C) model used as the reference method. Design: Cross-sectional study. Setting: Outpatient University Laboratory, Lisbon, Portugal. Methods: A total of 32 girls (age: 15.1 +/- 0.3 years) and 46 boys (age: 15.3 +/- 1.2 years) athletes were measured. Body volume was assessed by ADP; bone mineral content was assessed by DXA; and total-body water was assessed by deuterium dilution. Statistical analyses included examination of the coefficient of correlation (r), standard error of estimation (s.e.e.), slope, intercept, and pure error ( p. e.) and the agreement between models. Results: For boys and girls, differences between the 5C model and ADP %BF were 0.2 and 1.7% (r = 0.86 and 0.98, s.e.e. = 2.50 and 1.55%, p.e. = 2.77 and 2.23%), respectively. Differences between the 5C model and DXA % BF were -1.0 and -3.7% (r = 0.85 and 0.91, s.e.e. = 2.60 and 2.91%, p.e. = 2.90 and 4.66%), for boys and girls, respectively. For girls, regression between ADP and DXA against the reference method did not differ from the line of identity (P > 0.05) while for boys differences were found (P > 0.05). Dual energy X-ray absorptiometry overestimated % BF, particularly in girls. For both genders, large limits of agreement were found between the reference method and both techniques, with the exception of ADP in female athletes. Conclusion: We conclude that the two techniques were not precise for individual % BF prediction, though ADP revealed better agreement for girls. However, considering all performance criteria for the mean group, our analysis highlights ADP as a valid and nonbiased tool for the evaluation of body composition in adolescent athletes.