Comparisons between skeletal muscle imaging techniques and histology in tracking midthigh hypertrophic adaptations following 10 wk of resistance training

Abstract

This study had two aims. Aim1 was to determine the agreement between midthigh vastus lateralis (VL) cross-sectional area measured by ultrasound (mCSA_US) versus magnetic resonance imaging (mCSA_MRI) at a single time point, and the ability of each to detect hypertrophic changes. Aim2 was to assess the relationships between pre- and posttraining changes in thigh lean mass determined by dual-energy X-ray absorptiometry (DXA), VL mCSA_US, ultrasound-determined VL thickness (VL_Thick), and VL mean myofiber cross-sectional area (fCSA) with changes in VL mCSA_MRI. Twelve untrained males (age: 20 ± 1 yr, BMI: 26.9 ± 5.4 kg/m²; n = 12) engaged in a 10-wk resistance training program (2×/week) where right midthigh images and VL biopsies were obtained before and 72 h following the last training bout. Participants' VL mCSA_MRI (P = 0.005), DXA thigh lean mass (P = 0.015), and VL_Thick (P = 0.001) increased following training, whereas VL mCSA_US and fCSA did not. For Aim1, mCSA_US demonstrated excellent concordance [concordance correlation coefficients (CCC) = 0.830] with mCSA_MRI, albeit mCSA_US values were systematically lower compared with mCSA_MRI (mean bias: -2.29 cm²). In addition, PRE-to-POST VL mCSA changes between techniques exhibited good agreement (CCC = 0.700; mean bias: -1.08 cm²). For Aim2, moderate, positive correlations existed for pre-to-post changes in VL mCSA_MRI and DXA thigh lean mass (r = 0.580, P = 0.048), mCSA_US (r = 0.622, P = 0.031), and VL_Thick (r = 0.520, P = 0.080). A moderate, negative correlation existed between mCSA_MRI and fCSA (r = -0.569, P = 0.054). Our findings have multiple implications: 1) resistance training-induced hypertrophy was dependent on the quantification method, 2) ultrasound-determined mCSA shows good agreement with MRI, and 3) tissue-level changes poorly agreed with mean fCSA changes and this requires further research.NEW & NOTEWORTHY This is the first study to comprehensively examine how different midthigh muscle imaging techniques and histology compare with one another in participants that performed 10 weeks of resistance training. Our study suggests that histology results show poor agreement with results yielded from other common muscle imaging techniques, and researchers should be aware of this limitation.

Keywords: MRI; dual-energy X-ray absorptiometry; histology; muscle; ultrasound.