## 2 Materials and Methods
### Exercise Selection  
Eight exercises were selected: Squat, Front Lunge, Side Squat, Single Leg Deadlift, Lateral Arm Raise, Reverse Fly, Jumping Jacks, and Leg Extension Crunch. The main objective of the exercise selection was to create a full-body workout to track all selected joints from different angles. All exercises were tested for the suitability of tracking in both systems to ensure stable tracking of the angles. Both ARKit and the Vicon system exposed problems with the correct detection of exercises, where more extensive parts of the body were hidden from the cameras, for example, push-ups, and were therefore excluded. The testing was done in two steps: (1) We manually inspected the screen recording to see if the ARKit app model recognized the subject. (2) We checked the screen recording to whether the ARKit model overlayed with the subject's body parts during all parts of the exercise and whether the Vicon system could track all markers in the majority of recorded frames so that the full joint trajectory could be calculated. Only if both requirements were fulfilled, we selected the exercise for the study. The final exercise selection included eight exercises. Their execution (E, see Figure 1) and targeting muscle groups (TMG) are explained in the following, and tracked joint angles (TJA) are explained in the following. (I) Squat: (E:) The subject starts this exercise in an upright standing position. The subject squats down from the starting position by flexing the ankle, knee, and hip without movement compensations such as flexing the trunk and raising the heel. Each subject was asked to hold their arms stretched in front of the body. (TMG:) This exercise targets the lower body, especially the gluteus, quadriceps, hamstrings, and calves. (TJA:) The tracked joint angles include the left and right hip, and left and right knee. (II) Front Lunge: (E:) The starting position of the exercise is an upright standing with spreading legs front and back. The arms' position is the same as the squat. From the starting position, the subject goes down by flexing the ankle, knee, and hip in the front leg, flexing the knee and hip, and raising the heel in the back leg. (TMG:) This exercise targets lower body muscles, especially the gluteus, quadriceps, hamstrings, and calves. (TJA:) The tracked joint angles include the left and right hip, and left and right knee. Figure 1: The execution of all eight exercises as seen from the frontally positioned iPad. The body orientation was chosen to maximize the visible parts of the body. (III) Side Squat: (E:) The starting position of the exercise is an upright standing with spreading legs laterally. The arms' position is the same as the squat. From the starting point, the subject squats down with either side with either leg while the other leg is kept straight. (TMG:) This exercise targets similar muscle groups to squats, focusing on adductor muscles. (TJA:) The tracked joint angles include the left and right hip, and left and right knee. (IV) Single Leg Deadlift: (E:) The starting position of the exercise is an upright standing with a single leg. The arms' initial position is the same as in the Squat. Th subject leans forward from the starting position by flexing the hip with minimum knee flexion. As the subject leans forward, the arms should be hung in the air. The other side of the leg in the air should be extended backward to maintain balance as the subject leans forward. (TMG:) The exercise targets lower body muscles, especially the hamstring and gluteal muscles. (TJA:) The tracked joint angles include the left and right hip, and left and right knee. (V) Lateral Arm Raise: (E:) The subject starts the exercise in an upright standing position. Then, the subject laterally abducts the arms. (TMG:) The exercise targets upper body muscles, especially the deltoid muscles. (TJA:) The tracked joint angles include the left and right shoulder, and left and right elbow.