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DXA Predicts Minimum Weight in High School Wrestlers: 1470Board #109 9:30 AM – 10:30 AM

Clark, R. Randall; Sullivan, Jude C.

Medicine & Science in Sports & Exercise: May 2006 - Volume 38 - Issue 5 - p S208
Wednesday Morning Poster Presentations: Posters displayed from 7:30 a.m.–12:30 p.m. One-hour author presentation times are staggered from 9:30–10:30 a.m., 10:30–11:30 a.m., and 11:30 a.m.–12:30 p.m.: A-29 Free Communication/Poster – Exercise in Youth WEDNESDAY, MAY 31, 2006 9:30 AM – 12:30 PM ROOM: Hall B

University of Wisconsin Hospital Sports Medicine Center, Madison, WI.


In 1989, the Wisconsin Inter scholastic Athletic Association (WIAA) implemented a minimum weight (MW) rule that served as a model for other states and the National Collegiate Athletic Association (NCAA). The rule was implemented to minimize unhealthy weight loss practices and requires assessment of body composition prior to the season. The National Federation of State High School Associations (NFHS) has recommended that all state high-school athletic associations adopt a MW program by the 2006 season. This will impact approximately 250,000 high-school wrestlers across the United States. As a result, several methods, including DXA, have been suggested to predict MW in high school wrestlers. Before methods are adopted, their validity must be thoroughly and independently evaluated as each state will determine an appropriate method for assessing body composition.

PURPOSE: To evaluate the accuracy, precision and systematic bias of DXA prediction of MW in high school wrestlers. Secondarily, the DXA prediction error was compared to the currently approved skinfold (SF) method as well as bioelectrical impedance (BIA).

METHODS: Criterion MW was calculated by hydrostatic weighing (HW) with measured residual lung volume by O2 dilution. Whole body scans were performed with a Norland XR-36 bone densitometer. Skinfolds were taken by the same experienced measurer using the Lohman equation for body density and Brozek conversion to % fat. MW was calculated at 7% relative body fat for all methods. Subjects were 94 Wisconsin high school wrestlers (mean±SD; age=15.1±1.2yr, ht=170.3±7.1cm, wt=63.2±9.6kg).

RESULTS: There was no significant difference in mean MW from DXA (60.6±9.0 kg) and the HW criterion (59.8±9.0 kg). The correlation was strong (r=0.98) and the regression for the relationship between HW and DXA (y = 0.976xDXA+0.698 kg) did not significantly deviate from the line of identity. Bland Altman analysis showed no bias in the prediction of MW across the weight classes. A low total error (TE) of 1.9 kg was found with residuals ranging from −3.94 to 2.88 kg. DXA predicted MW within 1.9 kg (4.18 lb) 68% of the time and within 3.8 kg (8.36 lb) 95% of the time in this sample.

CONCLUSION: Because the regression of DXA vs HW was not significantly different than the line of identity, the prediction was considered accurate. A low TE of 1.9 kg suggests the precision was excellent and no systematic bias was found across weight classes. In practical terms the prediction error was superior to the SF method (2.1 kg) and BIA (2.8 kg) in the sample. We therefore conclude that DXA provided an 1) accurate, 2) precise and 3) valid prediction of MW without systematic bias in this sample of high school wrestlers.

© 2006 American College of Sports Medicine