Lean Soft Tissue Mass Measured Using Dual-Energy X-Ray Absorptiometry Is an Effective Index for Assessing Change in Leg Skeletal Muscle Mass Following Exercise Training

It is difficult to precisely and easily estimate the changes in skeletal muscle mass (SMM) following exercise training. We aimed to assess whether the change in lean soft tissue mass measured using dual-energy X-ray absorptiometry (DXA) reflects the change in SMM measured using magnetic resonance imaging (MRI) following exercise training in both the leg and trunk regions. Anthropometry, DXA, and MRI measurements of the trunk and leg regions were obtained in 10 male college sumo wrestlers before and after exercise training (mean duration between measurements: ~2 yr). Contiguous magnetic resonance images with 1-cm slice thickness and without gap were obtained from the first cervical vertebra to the ankle joints as reference data. Skeletal muscle volume was calculated from the summation of the digitized cross-sectional areas. The volume measurements were converted into mass by using an assumed skeletal muscle density (1.041 g/cm³). Trunk and leg areas, using DXA regional computer-generated lines, were adjusted to coincide with each discrete region by using MRI. Although the change in the DXA-measured lean soft tissue mass in the trunk region was significantly different from that of the MRI-measured SMM (Cohen's d = −1.3145, concordance correlation coefficient = 0.26, p < 0.01), the changes were similar in the leg region (Cohen's d = 0.07, concordance correlation coefficient = 0.87, p = 0.88). The exercise training-induced change in lean soft tissue mass significantly correlated with that in SMM, both in the leg (r = 0.88, p < 0.01) and trunk (r = 0.64, p < 0.05) regions. Bland–Altman analysis did not indicate a bias for the changes in leg lean soft tissue mass and SMM following exercise training. These results suggest that lean soft tissue mass measured using DXA is an effective index for assessing change in leg SMM following exercise training.