Objective To investigate the protective effect of calycosin on microgravity-induced muscle atrophy by using real-time shear wave elastography(RT-SWE).Methods The potential key active compound calycosin of anti-muscular atrophy in Astragali Radix was screened by systematic pharmacology.Eighteen healthy male Sprague-Dawley rats were divided into the control group[0.5%carboxymethyl cellulose-Na(CMC-Na)gavage],the hind limb unloading(HLU)+CMC-Na group(HLU+0.5%CMC-Na gavage),and the HLU+calycosin group(HLU+calycosin gavage)according to the method of random number table,with 6 rats in each group.After 28 d of continuous administration,the organ index,the toxicity of liver and kidney,the wet weight of soleus muscle and the ratio of muscle weight to body weight was measured,respectively.The non-invasive RT-SWE was used to evaluate the thickness and elastic modulus of rectus femoris in each group and the one-way analysis of variance was used to compare the differences among groups.Results There was no significant difference in organ index,liver and kidney toxicity among different groups of rats(all P>0.05).There were significant differences in the weight of soleus muscle and the ratio of muscle weight to body weight among different groups of rats(F=60.66,56.44,both P<0.001).Compared with the HLU+CMC-Na group,the weight of soleus muscle and the ratio of muscle weight to body weight in the HLU+calycosin group increased,and the differences were significant(both P<0.01).The thickness and elastic modulus of rectus femoris of rats in different groups were significantly different(F=35.47,14.68,both P<0.001).Compared with the HLU+CMC-Na group,the muscle thickness and elastic modulus of rats in HLU+calycosin group were increased,and the differences were significant(both P<0.01).Conclusions The treatment of calycosin has no side effects on rats.It can improve the thickness and elastic modulus of rectus femoris,and effectively prevent microgravity-induced muscle atrophy,which may provide a new candidate drug for astronaut muscular atrophy.