Fig. 1

Ultrasound image of cross-sectional area of the gracilis muscle. The white arrows indicate muscle cross-section area (CSA). a Pre-transplantation rest state; b Pre-transplantation contraction state; c post-transplantation rest state; d post-transplantation contraction state. The ratio of pre- to post-transplant CSA value of gracilis muscle at rest state was defined as muscle bulk ratio (MBR). The ratio of CSA value at the contraction state to that at rest state was defined as contraction ratio (CR). The CR values of gracilis muscle before and after transplantation were defined as CR-2 and CR-1, respectively. MBR = CSA in c/CSA in a; CR1 = CSA in d/CSA in c; CR2 = CSA in b/CSA in a