Ultrasound-assessed thigh fat thickness is valid for estimating body fat percentage in Division I collegiate female athletes.

Objectives: Monitoring body composition can help to optimize performance in female athletes. This study aimed to create a conversion equation between dual-energy X-ray absorptiometry-measured body fat percentage and ultrasound-measured subcutaneous thigh fat thickness in Division I female athletes as a more accessible, cost-effective alternative.

Design: Cross-sectional study.

Methods: We enrolled 82 Division I female athletes. Dual-energy X-ray absorptiometry was used to assess body fat percentage. Bilateral panoramic thigh ultrasound scans at 50 % of the femur length were used to calculate subcutaneous fat thickness overlying the rectus femoris muscle. The dataset was divided into a training (70 %, n = 57) and holdout (30 %, n = 25) sample to develop and validate the conversion equation, respectively. Using the training sample, a stepwise, linear regression was used to predict dual-energy X-ray absorptiometry body fat percentage from ultrasound fat thickness, mass, and height. Beta coefficients from this model were used to create a conversion equation. After applying the conversion equation to the holdout sample, intraclass correlation coefficients (ICC_2,k) and Bland-Altman plots were used to establish the agreement between the ultrasound-estimated and DXA-derived percent body fat.

Results: Within the training sample, dual-energy X-ray absorptiometry was significantly associated with ultrasound fat thickness, height, and mass (F = 31.9; p < 0.001; R² = 0.64). Within the holdout sample, when using the conversion equation to estimate body fat percentage, we found a strong agreement between estimated and DXA-derived percent body fat (ICC_2,k = 0.93; 95 % CI: 0.83-0.97).

Conclusions: Ultrasound-assessed subcutaneous thigh fat thickness predicts dual-energy X-ray absorptiometry-assessed body fat percentage in Division I female athletes.