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

This study had two aims. AIM1 was to determine the agreement between mid-thigh vastus lateralis (VL) cross-sectional area measured by ultrasound (mCSAUS ) versus magnetic resonance imaging (mCSAMRI ) at a single time point, and the ability of each to detect hypertrophic changes. AIM2 was to assess the relationships between pre-to-post training changes in thigh lean mass determined by DXA, VL mCSAUS , ultrasound-determined VL thickness (VLThick ), and VL mean myofiber cross-sectional area (fCSA) with changes in VL mCSAMRI . Twelve untrained males (Age: 20±1 y, BMI: 26.9±5.4 kg/m2 ; n=12) engaged in a 10-week resistance training program (2x/week) where right mid-thigh images and VL biopsies were obtained prior to and 72-hours following the last training bout. Participants' VL mCSAMRI (p=0.005), DXA thigh lean mass (p=0.015), and VLThick (p=0.001) increased following training, whereas VL mCSAUS and fCSA did not. For AIM1, mCSAUS demonstrated excellent concordance (CCC = 0.830) with mCSAMRI , albeit mCSAUS values were systematically lower compared to mCSAMRI (mean bias: -2.29 cm2 ). Additionally, 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 mCSAMRI and DXA thigh lean mass (r=0.580, p=0.048), mCSAUS (r=0.622, p=0.031), and VLThick (r=0.520, p=0.080). A moderate, negative correlation existed between mCSAMRI and fCSA (r=-0.569, p=0.054). Our findings have multiple implications: i) resistance training-induced hypertrophy was dependent on the quantification method, ii) ultrasound-determined mCSA shows good agreement with MRI, and iii) tissue-level changes poorly agreed with mean fCSA changes and this requires further research.