In daily lives, humans successfully transit their motions rather than performing separate movements. It has been widely acknowledged that there are four and five modules (called muscle synergy) in human sit-to-stand and walking motions, but it was still unclear how humans activate their redundant muscles to transit their movement from sitting to walking. Therefore this study hypothesize that human sit-to-stand can be explained from muscle synergies of sit-to-stand and walking motions, and we perform the experiment to verify it. Firstly, four and five muscle synergies were obtained from sit-to-stand and walking motion, and it has been tested whether these nine synergies are applicable to sit-to-walk motion. Results showed that sit-to-walk motion were successfully explained from nine synergies. Moreover, it was shown that humans adaptively changed the activation time of each synergies to delay body extension time and to generate necessary initial momentum for the walking motion.