Alteration in the cross-sectional cortical area and the cortical thickness with and without knee loading at 5, 10, 15 and 20 Hz. The results are expressed as mean ± SEM. The single, double, and triple asterisks indicate p < 0.05, p < 0.01 and p < 0.001 in Fisher's PLSD, respectively. (A) Cross-sectional cortical area (mm2). (B) Increase in the cross-sectional area (% of control). (C) Cortical thickness (mm). (D) Increase in the cortical thickness (% of control).