## 4 Discussion  
Heading the ball is a fundamental aspect of soccer but exposes players to repeated sub-concussive impacts. Given the growing concerns surrounding the long-term sequelae attributed to heading, it is crucial to understand the biomechanics of header impacts and how they vary across different in-game contexts. To achieve this, we used custom-fit iMGs in combination with qualitative video analysis to identify on-field heading scenarios associated with higher HAE magnitudes. Our findings provide initial insight for the development of player protection strategies based on the principle that reducing the magnitudes of HAEs may potentially mitigate the adverse effects of heading on brain health. The current study revealed no significant variations in head kinematics among differing header types, aligning with the results of previous research in female collegiate players [6]. However, it is important to note that our study only examined HAEs during games, yet previous research has shown that HAEs during practice can be just as significant [1]. This highlights the need for monitoring HAE during both practices and games, as reducing heading frequency during practices may be a more effective way to lower overall HAE exposure and severity. Currently, efforts to reduce HAEs have mainly focused on goal kicks [36]; however, prior research found them to occur infrequently and thus not significantly contribute to the cumulative heading load experienced by athletes [37]. Instead, Harris et al. [37] noted that aerial passes made up the largest portion (41%) of headers executed by players, a trend our study also confirmed at 45.1%. By limiting the number of practices in which athletes participate in aerial passes, we may be able to reduce head acceleration exposures. This notion is supported by a study of youth football athletes that demonstrated a 37% reduction in the number of head contacts when limiting contact in practices to one-third of the total practice time [38]. However, a direct measure of HAE exposures within heading-restricted training sessions has yet to be conducted and represents an important future consideration. Another approach to decrease HAEs in soccer is to identify and alter the in-game contexts that are associated with the most severe headers. Previous research utilizing multi-body models has established that the force experienced during header impacts is primarily derived from the velocity of the ball rather than its mechanical properties [39]. The current research supports this finding, as goal kicks, which tend to result in the highest heading ball speeds [40], were found to have significantly greater resultant PAA than long balls or pass attempts. Similarly, comparable iMG studies in women's collegiate soccer have revealed significant differences in mean peak rotational acceleration between headers from goal kicks and those during live-play scenarios [6]. Given these findings, modifications to goal kicks present a unique opportunity to decrease the peak speeds at which players head the ball, thereby reducing the cumulative exposure to head acceleration. Player protection strategies  
Figure 3: Heading kinematics based on the ball delivery methods cross (n = 13), goal kick (n = 18), long ball (n = 42) and pass (n = 60). Asterisks (*) indicate statistical significance between goal kicks and both long balls (\(p\) = 0.024) and pass attempts (\(p\) = 0.011). Tabulated results are available in Appendix A.  
such as replacing goal-kicks with roll-outs or head height rules at certain levels of play could mitigate the most severe headers [40; 41]. Additionally, strategies may include changes in regulations, such as the Football Association's 2019 introduction of allowing a teammate to be within the penalty area when the goal kick takes place [42]. This change was initially intended to limit in-match pauses, but researchers subsequently observed a decrease in the frequency of long goal kicks as a result [43].