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Publication Date


Type of Culminating Activity

Thesis - Boise State University Access Only

Degree Title

Master of Science in Exercise and Sports Studies, Biophysical Studies



Major Advisor

Dr. Werner W.K. Hoeger


Introduction. The assessment of body composition, specifically percent body fat (PBF), is important in the establishment of normal weight, excessive weight, and obesity. Excessive body weight and obesity are risk factors for many chronic conditions that currently afflict most adults in the U.S. and most developed countries throughout the world. Several methods are used to determine body composition and PBF. Hydrostatic weighing (HW) has been the “gold standard” to determine PBF in exercise physiology laboratories the last few decades. A relatively new technique to assess PBF is the air-displacement plethysmography (ADP) technique, commonly determined through the use of the Bod Pod unit. While the validity of the Bod Pod has been reported in the literature, the results are conflicting. Preliminary data collected on the campus of Boise State University seemed to question the validity of the ADP technique in the assessment of PBF.

Purpose. The purpose of this investigation was to determine if there is a significant difference between PBF as determined through ADP and HW.

Research Design. Eighty (n = 80) healthy male- and female-Caucasian subjects between the ages of 18 and 40 years were tested in the Human Performance Laboratory for PBF according to ADP and HW. The subjects were divided according to gender and body mass index (BMI) into six groups: normal weight (NW), overweight (OW), and obese (OB) groups. Pearson's correlation was used to determine the relationship between ADP and HW and Repeated Measures ANOVA was used to determine whether there were statistically significant differences between the two estimates of PBF.

Results. PBF results for NW, OW, and OB men respectively according to ADP and HW were: 16.3 vs. 11.4, 21.7 vs.17.7, and 34.2 vs. 30.7. For NW, OW, and OB women the respective results according to ADP and HW were: 26.9 vs. 20.5, 33.2 vs. 30.4, and 37.4 vs. 34.2. Strong positive correlations were found between ADP and HW for all groups in the assessment of PBF (r =.829 to .990). Significant differences (p < .05), however, were found between ADP and HW in every group except in the obese women group. The latter result may be due to the low number of subjects in this group (n = 3).

Conclusion. Based on these results, the ADP technology is not an accurate technique to assess PBF, specially in research conditions. Further technical work needs to be conducted to make ADP an acceptable technique for body composition assessment.