This paper focuses on the use of inertial measurement unit in range of motion rehabilitation for estimating the shoulder joint angle. Such a device provides an objective means of measurement and makes remote or at home range of motion rehabilitation possible by using an assistive software. In practice, however, without expert assistance, patients can mistakenly select tho wrong protocol in tho software and unintentionally performing another protocol, resulting in an inaccurate result. An automatic detection of rehabilitation protocols during rehabilitation process is, therefore, introduced. It can automatically guide the patients toward the actual rehabilitation protocol. In addition, the information can be applied to ensure that all the required steps or protocols, formally specified by tho therapist, are performed by tho patients.