## 4 Discussion
Data from the current study suggests that relying on total vertical force traces may lead to misclassification of strike patterns. Specifically, in-shoe total plantar force data revealed no distinct impact peaks for midfoot or heel strike peaks (Figure 4), despite clear distinctions in spatial zone differences in peak impact and average loading rate (Figure 5). These spatial differences aligned consistently with the designated strike pattern (Figure 5A,B). The posterior zone exhibited the highest-magnitude impact peak and average loading rate in the heel strike, the anterior zone dominated in the forefoot strike, and midfoot strike displayed a more even distribution where the posterior zone remained dominant (Figure 5). These within-strike pattern distinctions highlight the value of using spatial force data to accurately identify foot strike pattern and advanced spatial and spectral analysis to assess impact kinetics during running interventions. Spectral analysis has been used to separate the true (high-frequency) impact component of the total force signal from that of the active processes [26; 27] that occur during limb deceleration. Figure 6A supports the presence of a low-frequency active process component but suggests it may not significantly influence the overall kinetic signal. Alternatively, it could be that within the same participants, strike pattern did not alter the active processes. Nonetheless, strike pattern had a significant effect on peak impact, average loading rate (Table 1), and the high-frequency PSD. Interestingly, the midfoot strike had significantly greater values than either the heel or forefoot strike, despite most participants being natural midfoot strikers (Figure 2) based on the classification criteria (Figure 5C). This contrasts with previous research that has focussed on natural strike pattern preferences or overground running, which reports lower impact kinetics in midfoot and forefoot striker patterns [6; 27; 43]. It is possible that the instructions given to run flat-footed produced a gait distinct from participants' habitual midfoot style, potentially increasing vertical limb acceleration and thereby amplifying impact deceleration. This is supported where peak impact accelerations were greater in midfoot than rear or forefoot strike patterns [44]. However, stride duration, ground contact time and swing time showed no significant differences across conditions, suggesting that gross temporal mechanics remained stable. Although not a primary focus, the small, non-significant decrease in swing time (Table 1) warrants further exploration from a kinematic perspective. Additionally, spatial analysis of the high-frequency component revealed similarity with peak impact (Figure 5A) and average loading rate (Figure 5B), but with notable differences in zone contributions. Specifically, in the heel and forefoot strikes, non-dominant zones contributed less (Figure 6B). This suggests that the low-frequency components may inflate non-specific zone data during impact. Although this study primarily focused on comparing strike pattern with respect to impact kinetics and force signal characteristics, active peak force associated with propulsion was also measured. The results showed significantly lower active peak force in heel strikes compared to midfoot and forefoot strikes, in both total and spatial zone measures (Tables 1 and 2). These findings contrast with previous work where there were no differences between total forces across strike patterns [43]. However, the data presented shows considerable posterior and central zone contributions to total force in both heel and midfoot strikes, indicating differences in plantar surface mechanics. While no spatiotemporal differences were observed between foot-strike patterns using this specific shoe during treadmill running, and total force trace structure appeared similar when measured by in-shoe devices, distinct differences for impact kinetic variables between strike patterns were present, particularly when examined using frequency domain analysis.