Associations between ultrasound-derived muscle morphology, adiposity, and VO _2max in young, trained runners: An exploratory cross-sectional study

Objective: This exploratory cross-sectional study examined how muscle thickness and echo intensity of quadriceps and calf musculature are associated with maximal oxygen consumption (VO 2max ) in trained runners. Methods: Male and female runners ( n = 25; 22 ± 3.0 years; 150–300+ min running per week) participated in this study. Participants’ rectus femoris, vastus intermedius, vastus lateralis, and medial gastrocnemius were imaged via B-mode ultrasound and analysed for muscle thickness, corrected echo intensity, and subcutaneous adipose tissue. Participants then completed an incremental treadmill test. Associations between muscle thickness, corrected echo intensity, and VO 2max were determined using Pearson’s correlation coefficient. Multiple linear regression was used to determine whether muscle thickness, corrected echo intensity, or subcutaneous adipose tissue were predictive of VO 2max . Results: VO 2max was not associated with muscle thickness. VO 2max was positively associated with corrected echo intensity of the medial gastrocnemius ( r = 0.413; p = 0.04). In addition, VO 2max was negatively associated with body mass index ( r = −0.670), fat mass ( r = −0.791), body fat percentage ( r = −0.707), and subcutaneous adipose tissue of the vastus lateralis ( r = −0.436; all p < 0.05). Stepwise multiple linear regression indicated corrected echo intensity of the medial gastrocnemius ( F = 4.14, p = 0.047, R = 0.409, R 2 = 0.167) and corrected echo intensity of the medial gastrocnemius and vastus lateralis ( F = 4.79, p = 0.019, R = 0.560, R 2 = 0.314) were the strongest predictors of VO 2max . Conclusion: VO 2max was not associated with muscle thickness of lower extremity musculature, but was associated with subcutaneous adipose tissue, corrected echo intensity, and more favorable whole-body fat mass and deposition in young, trained runners.