Ultrasound-derived muscle thickness and muscle quality parameters vary across regions of the vastus lateralis in physically active and endurance-trained men

purpose This study primarily investigated differences in muscle thickness (MT), corrected echo intensity (cEI), subcutaneous fat thickness (SFT) and predicted fat fraction (FF%) across regions/sites of the vastus lateralis (VL) muscle. A secondary exploratory aim was to compare these parameters between endurance-trained and physically active men groups. Methods Measurements were obtained from four groups of men (physically active individuals, cyclists, runners, and triath- letes; n = 26; 29.2 ± 8.4 y, 75.3 ± 12.3 kg, 176.8 ± 8.3 cm). Panoramic B-mode ultrasound was used to assess cEI and FF% at 0–25%, 25–50%, 50–75% and 75–100% of the muscle length. MT and SFT were assessed at the midpoints of each region (12.5%, 37.5%, 62.5%, and 87.5%). One-way repeated-measures ANOVA compared regions and sites with pooled groups, while one-way ANOVA compared groups. Results cEI was significantly lower in the middle (25–75%) than in both the distal (0–25%) and proximal (75–100%) regions (p ≤ 0.002, g = 0.61–0.79). FF% was higher in the proximal region than in all other regions (p ≤ 0.025, g = 0.61–0.92), and higher at 25–50% than 0–25% (p = 0.011, g = 0.31). SFT was greater at 87.5% than at all other sites (p < 0.001, g = 1.97– 2.45), while MT was higher at 37.5% and 62.5% than at 12.5% and 87.5% (p < 0.001, g = 0.94–2.60). Exploratory group comparisons showed no significant differences in any parameter (p > 0.05). Conclusion All parameters may vary along the VL muscle belly. Ultrasound-derived assessments of muscle architecture and quality based on a single measurement site/region should be interpreted with caution.