Fiber cross-sectional area in each group measured from the images of SDH staining. Values indicate mean ± SEM. The symbols * and † significant differences from the Con and HU groups, respectively, at p < 0.05. Con control group, HU hindlimb unloading group, HU + AX hindlimb unloading plus astaxanthin treatment group, HU + ES hindlimb unloading plus electrical stimulation group, HU + AX + ES hindlimb unloading plus astaxanthin treatment with electrical stimulation group, SEM standard error of mean