###### Abstract
A transfer of velocity from distal to proximal is critical in maximizing distance in throwing [7; 8]. Theoretically, increased trunk motion may allow more energy to be transferred from the trunk to the throwing arm, and eventually to the axe, which may lead to an increase in velocity. The trunk musculature includes the rectus abdominis, external oblique, internal oblique, and transverses abdominis. The roles of this musculature in throwing are to promote dynamic stabilization, rotation, lateral bending, and flexion/extension of the trunk [4]. The magnitude of the center of mass (CoM) acceleration is a proxy measurement for the impact forces experienced at the trunk that is commonly used by clinicians and researchers. The trunk and the theoretical CoM transfer and control force and motion in an  
Figure 1: Illustration of the motion involved during the one-handed overarm axe throw. integrated kinetic chain and are important in throwing tasks. The acceleration of the trunk CoM occurs in three dimensions, often referred to with respect to a local CoM coordinate frame: Axial (vertical), anterior-posterior, and mediolateral [9]. In this way, the body system may be characterized, from a mechanical perspective, by its CoM. The CoM is the unique point in whose linear acceleration is determined only by the total external force acting on the system. When applied to the CoM, such force causes a linear acceleration without angular acceleration. Microelectromechanical system (MEMS) technology is the technology of microscopic devices, which typically incorporates accelerometers, gyroscopes, and a magnetic field sensor (magnetometer). This technology allows one to infer motion of the CoM via magnitudes of trunk CoM acceleration based on different forms of human movement (e.g., [10; 11]). To be successful in competition, axe throwers must achieve appropriate changes in upper body movement, including angle of release, projection height, and release speed, to optimize the throwing velocity of the axe. In this regard, general throwing is a goal-related task and, depending on the objective, the velocity and kinematic profiles change accordingly [12]. Yet such kinematic profiles are subject to change depending on both the gender and relative skill level and experience of the thrower. Akin to other throwing sports, the end effector (e.g., hand/racket) velocity profiles depend on the skill level of the thrower [13] and the throwing technique [8]. Though, to the best of our knowledge, no research has addressed the idea of attempting to measure trunk kinematics via accelerations of the CoM or determine its effect on performance characteristics in axe throwing. Additionally, no study has examined the differences in trunk kinematics between male and female axe throwers of varying skill levels for performance purposes. This directs us to the question: What changes to trunk CoM acceleration demonstrate appropriate magnitudes that are specific enough to promote accuracy in performance characteristics between male and female throwers? These data may provide an estimation of the efficacy of trunk performance in respect to producing a specific training effect for improving throwing performance. Therefore, the purpose of this study was to examine the magnitude of differential trunk CoM acceleration in male and female axe throwers of varying skill levels while they performed five overarm axe throws, and to compare the trunk CoM kinematics demonstrated in actual throwing performance.