## 2 Materials and Methods  
This cross-sectional and observational pilot study design examined the magnitude of triaxial trunk CoM acceleration and thus upper torso kinematics in five sequential one-handed overarm axe throwing movements and compared with overall throwing performance, that is--throwing accuracy. A sample of ten (\(n=10\); 5 males and 5 females) right-handed axe throwers participated in this preliminary study, having given informed consent, with approval by the University Research Ethics Committee (HREC21114). All participants were members of the same semi-professional axe throwing team. All participants trained at least once per week and had previously played and/or competed in at least one scheduled axe throwing league game in the past regulation season. Participants were excluded from the study if they had any injury (acute or chronic) or illness at the time of the study that prevented them from exerting maximum effort. Both male and female players over the age of 18 years were asked to partake in this study. The participants were informed that they could withdraw from the study at any time without penalty. For the time of the study, all participants were in physically good condition and reported no injuries or pain. The athletes were of various performance levels. Each participant had at least one year of training experience. Two of the participants had previously qualified to represent Australia at the 2022 International Axe Throwing Championship (IATC) (held in Toronto, Canada). All participants were right hand-dominant. Dominance was defined by the individuals throwing arm preference, which was self-determined and visually confirmed by the principal author once informed consent was received. Prior to testing, anthropometric details, including height and body mass, were recorded. Height and weight were measured without shoes to the nearest 0.1 cm and 0.1 kg, respectively [14]. The anthropometric and training characteristics of the participants were taken and recorded by the principal authors. The anthropometric measurements are depicted in Table 1.  
Testing was conducted during the start of the participants' ten-week competitive season (i.e., week 1). All testing of the axe throwers commenced at 1700 in their customary axe throwing venue to ensure that their regular and scheduled throwing activity pertaining to the season was not interrupted. Data were collected under similar environmental conditions (17-18 \({}^{\circ}\)C, 45-55% relative humidity). The participants wore a loose-fitting t-shirt or singlet combined with either short or sweat (tracksuit) pants. After completing the informed consent and health history forms, the participants were asked to perform a general and self-directed warm-up. The warm-up included dynamic upper body stretching that was combined with approximately six practice throws of the axe. To assess the impact of the trunk CoM during the five axe throws, one inertial measurement unit (IMU) was manually placed to sit at each participant's spinous process (i.e., a total of 10 accelerometers were used). Specifically, the accelerometer was aligned with the lumbar five (L5) sacrum one (S1) position [15] with the y-axis in alignment with the cervical vertebra (Figure 2). The accelerometer was secured into a moisture-proof ziplocked metallic matte foil airtight bag (Ferenli, Miami, FL, USA). The bag was attached using double-sided adhesive tape to ensure fixation and to reduce unwanted movement. [15]. The magnitude of acceleration was measured using the ActiGraph GT9X + accelerometer (ActiGraph, LLC, Pensacola, FL, USA). This device (3.5 \(\times\) 3.5 \(\times\) 1 cm, 14 g) was initialized to record accelerations at a sampling frequency of 100 Hz. Orientation of the sensor was to capture data in the three orthogonal directions, specifically in the vertical (y, upward-downward), anteroposterior (x, forward-backward), and mediolateral (z, side to side) directions (in m/s\({}^{2}\)).