Subcutaneous Thigh Fat Assessment: A Comparison of Skinfold Calipers and Ultrasound Imaging

Context: Skinfold calipers (SC) typically are used to determine subcutaneous fat thicknesses. Identifying the exact separation of muscle and fat can complicate measurements. Ultrasound imaging (USI) might provide a better technique for analyzing subcutaneous fat thicknesses. Objective: To compare measurements from SC and USI in assessing subcutaneous thigh fat thickness. Design: Descriptive laboratory study. Setting: Laboratory. Patients and Other Participants: Twenty healthy adults (13 men, 7 women; age = 26.9 +/- 5.4 years, height = 173.9 +/- 7.3 cm, mass = 77.4 +/- 16.1 kg) participated. Intervention(s): Participants were seated in 90 degrees of knee flexion and 85 degrees of trunk extension. A standardized template was used to identify measurement sites over the vastus medialis obliquus (VMO), distal rectus femoris (dRF), proximal rectus femoris (pRF), and vastus lateralis (VL). Three measurements at each of the 4 sites were made in random order and were averaged for each measurement tool by the same investigator. Main Outcome Measure(s): Fat thickness was measured in millimeters with SC and USI. Measurements at each site were compared using Pearson product moment correlations and Bland-Altman plots. Results: Strong correlations between measures were found at the VMO (r = .90, P < .001), dRF (r = .93, P < .001), pRF (r = .93, P < .001), and VL (r = .91, P < .001). Mean differences between measures ranged from 1.7 +/- 2.4 mm (dRF) to 3.7 +/- 2.6 mm (pRF), indicating that the SC resulted in larger thicknesses compared with USI. Limits of agreement, as illustrated by the Bland-Altman plots, were fairly wide at each site: from -3.38 mm to 7.74 mm at the VMO, from -3.04 mm to 6.52 mm at the dRF, from -1.53 mm to 8.87 mm at the pRF, and from -3.73 mm to 8.15 mm at the VL. All plots except for the VL demonstrated increasing overestimation via the SC as fat thicknesses increased. Conclusions: We found strong correlations between the SC and USI; however, the large limits of agreement and increasing mean differences with larger fat thicknesses were a concern in terms of using this tool. When measuring subcutaneous fat thickness of the thigh, SC tended to overestimate thickness in individuals with higher fat values.