*2.1. Overview*

This study consists of three sections, namely recruiting and selecting participants, capturing motion data of Baduanjin participants on IMU, and processing and analyzing the motion data. We invited teachers and students from a university in Southwest China to participate in the study. We divided them into three groups—teachers, novice students, and senior students. We captured motion data of all participants on IMU when they practised Baduanjin. The motion data were converted to quaternions and analysed in two di fferent ways. The first way was based on the quaternions of motion, where dynamic time warping (DTW) was used to calculate the distances between the quaternions of the teacher and the two groups of students (novice and senior). The motion accuracy of the students was expressed by distances. DTW is a classic similarity method to solve the time-warping issue in similarity computation of time series [27]. Compared with the other methods, namely the hidden Markov model (HMM) and symbolic aggregate approximation (SAX), the taken time of DTW is shorter [28,29]. Considering that, in the actual teaching, students need to ge<sup>t</sup> feedback information and a large number of student data in realtime, we adopted DTW in the study. The second way used the extracted key-frames to calculate distances. Based on the quaternions of key-frames, DTW was used to calculate the distances. Finally, based on data of the distances, an independent sample T-test or Mann–Whitney U test was used to define whether the motions of the two groups of students (novice and senior) were di fferent in motion accuracy (see Figure 1).

**Figure 1.** Flow diagram of the study.

#### *2.2. Recruiting and Selecting Participants*

In this study, we invited a martial arts PE teacher and undergraduate students to participate in the study. The inclusion criteria for participants are as follows:

Teacher: martial arts PE teacher, former national martial arts athlete, with an undergraduate and master's degree in traditional Chinese sports (martial arts specialization), and more than ten years' experience teaching Baduanjin.

Novice students: undergraduate students in the university with no experience of Baduanjin, without a disability and no clinical or mental illness.

Senior students: undergraduate students in the university who have passed Baduanjin in their PE course, without a disability, and no clinical or mental illness.

Participants read the information sheet that outlined the purpose and procedure of the study. Those who agreed to participate were given the consent form to sign.

#### *2.3. Capturing Motion Data of Participants on IMU*

Baduanjin is a traditional Chinese martial art for fitness. The speed of motions is relatively slow [30]. We used IMU to capture the motion data of the teacher, novice, and senior students for eight standard motions of Baduanjin as shown in Figure 2.

**Figure 2.** Eight standard motions of Baduanjin.
