## 1 Introduction
### Hand-Striking Techniques  
For this research, only striking techniques that can be executed wearing boxing gloves were considered. This is due to the composition of the RD \(\alpha\) system since the exact hand and finger positions cannot be identified like it is necessary for martial arts and combat sports such as kung fu [25] or karate [26] to differentiate between techniques. Thus, for the striking technique recognition, techniques from Boxing and Kickboxing were considered, which can be described as follows according to their rulebooks [27; 28]:* Straight (Jab/Punch) [29] (see Figure 1a,b): Executed with the leading (Jab) or rear hand (Punch/Cross) in a straight line from the guard position towards the target object.
* Hook [29] (see Figure 1c): Executed either with the lead or rear hand from the guard position by extending and then rotating the arm. In the end position, the upper and lower arm build approximately a 90-degree angle and are parallel to the ground.
* Uppercut [30] (see Figure 1d): Executed either with the lead or rear hand from the guard position by slightly lowering down and rotating the hand and subsequently moving it upwards with the help of the upper body.
* Backfist [31] (see Figure 1e): Most often used in pointfighting, which is a sub-discipline of kickboxing. The backfist is executed with the leading hand by extending the arm towards a target but with the intention to hit the target with the backside of the fist [31].
* Ridge hand [31] (see Figure 1f): The hand is rotated and moved in an arc trajectory with the intention to hit the target object with the back of the hand.  
All striking techniques can generally be split into three phases, the segment acceleration, the target contact, and the restoring phase [33]. For this paper, only the two former phases are relevant. The applied impact of a striking technique is the product of the effec  
Figure 1: Illustration of the selected striking techniques. Images created using Magic Poser [32]. (**a**) Straight/Jab. (**b**) Punch/Cross. (**c**) Hook. (**d**) Uppercut. (**e**) Backfist. (**f**) Ridge hand.  
tive mass of/behind the strike (\(m\)), the (negative) acceleration (\(a\)) during target contact, and the trajectory of the involved segments, during the target contact, see Equation (1).  
\[p=\int_{start}^{end}F=\int_{start}^{end}m*a \tag{1}\]  
Naturally, the negative acceleration of the glove is highly affected by the target (e.g., a comparison between the concrete wall and a soft punching bag). Furthermore, for each striking technique, the trajectory of the boxing glove differs, also resulting in different force profiles. These characteristics render the velocity before the target contact, the trajectory (acceleration and relative angle in all three directions), as well as the impact and potential peak force as crucial factors to determine the technique and target. Figure 2 shows the line chart of each feature over time of a jab. For comparison, five jab instances are plotted at once to depict the similarities between the curves. However, due to the positioning of the IMUs directly within the gloves, a solely rule-based differentiation between the techniques is not possible, as the rest-body movement is not known. This is why an ML-based approach might provide a solution to this problem.  
Figure 2: Illustration of five measurements of a jab technique depicting the sensor values over time. (**a**) Angular velocity. (**b**) Acceleration. (**c**) Velocity. (**d**) Force.