The Axe Factor: Exploring Differences in Trunk Motion During Axe Throwing

Background: Axe throwing is a relatively new sport in which competitors throw axes at a circular target, attempting to hit the central location (the bullseye). Points are allocated depending on where the axe lands on the board. Performance of the characteristic one-handed axe throw can involve the sequential activation of motion through a kinetic chain or link system. Trunk stability reflects an individual’s postural control and ability to orientate and stabilise the body using appropriate balance control strategies and responses. Therefore, trunk stability is important in throwing kinematics. However, the forward translation of the body system, as represented by the trunk centre of mass (CoM), during the one-handed axe throw remains an under-researched area amongst elite and amateur axe throwers. A greater understanding of trunk CoM motion may provide athletes and coaches with a critical analysis of the throwing technique, highlighting relevant factors for the future development of training programmes. Objective: This field-based study compared the magnitude of trunk CoM acceleration in the vertical, mediolateral, and anteroposterior directions between elite and amateur axe throwers during five characteristic one-handed overarm axe throws. An additional objective was to compare the relationship between acceleration magnitudes of the trunk CoM and throwing accuracy between elite and amateur throwers. Methods: Five elite and five amateur axe throwers (6 male, 4 females; age: 32 ± 7.7 yrs: body mass: 77.6 ± 6.95 kg; height:176. ± 9.8 cm; weekly training volume: 4 ± 1.1 h) participated in this study. This was an observational study design whereby each participant completed five single hand overarm axe throws using a standard axe (mass: 1.13 kg) as specified by the International Axe Throwing Federation. One inertial measurement unit (IMU, an accelerometer) was manually placed to sit at each participant’s spinous process (i.e., a total of 10 IMUs were used). Orientation of the accelerometer 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 gravitational acceleration, G, where 1 G is equal to 9.81 m/s2) Raw accelerometry signals from the trunk CoM were downloaded and then converted from gt3x files to CSV format and saved and exported to Microsoft Excel. Raw data were then analysed using the ActiLife software program. Findings: Significant differences (p < 0.001) in the magnitude of trunk acceleration were observed between the elite and amateur throwers. Specifically, lower magnitudes of trunk CoM acceleration were observed in the elite throwers combined with higher levels of accuracy. When throwing accuracy was considered against the total vector of trunk acceleration, significant differences were observed between the elite and amateur throwers (f = 11.67, p = 0.0269). Discussion: This is the first methodological study to discriminate between the magnitude of trunk CoM acceleration in axe throwers of varying skill levels. Practically, this could mean that throwers with an adequate lack of trunk control are more sensitive to changes to the magnitude of acceleration, that is – greater magnitudes of trunk CoM acceleration occur which result in less accuracy. The analysis of the magnitude of trunk acceleration may help improve the understanding of the whole athlete-thrower system in what remains an unexplored sport.