## 4 Discussion  
This study aimed to evaluate spatial and spectral plantar forces across foot-strike patterns. While no significant stride duration, ground contact time or swing time variations occurred between foot strike patterns, significant spatial differences in peak impact and average loading rate were evident, despite the absence of distinct peaks in the midfoot or  
Figure 6: Mean \(\pm\) SD data from power spectral density (PSD) of plantar forces for each strike pattern. (**A**). Comparison of the low-frequency (<10 Hz) and high-frequency (>10 Hz) PSD components, (**B**) high-frequency PSD distribution for the posterior, central, and anterior zones of the foot. - heel strike total force traces. As such, strike classification based on spatial data is more accurate than total plantar force during treadmill running. Further, the total high-frequency component of the PSD was greatest in midfoot and lowest in the forefoot strikes, with the posterior zone of heel strikes exhibiting largest individual zone power. Lastly, total peak active force and total impulse were greater in forefoot strikes than in midfoot and heel strikes. All participants were well trained, running -70 km\(\cdot\)wk\({}^{-1}\) at the time of the study, and successfully adopted the assigned footstrike techniques, as evidenced by the plantar force profiles. This level of experience and technique adaptability reinforces reliability of the dataset, enabling us to develop classification guidelines based on spatial distribution of impact forces specific to treadmill running (Figure 5C). Runners exhibiting \(>\)70% of impact in the posterior zone were classified heel strikers; \(>\)50% in the anterior zone as forefoot strikers; and those with \(<\)70% posterior, \(<\)50% anterior, but \(>\)25% in the central zone were classified as midfoot strikers. Based on these classification thresholds, our retrospective analysis of the cohort included four natural heel strikers and seven natural midfoot strikers (Figure 2). The adaptation of different strike patterns resulted in no within-subject differences to stride duration or its components, ground contact time or swing time. This agrees with comparisons between non-paired natural heel and forefoot strikers [34,35] and paired natural heel and unnatural forefoot strikers [30], and reflects a preferred movement path [36], whereby individuals modulate impact attenuation or force production from strike-specific spatial zones (Figure 5A,B, Table 2). However, this contrasts to observations where midfoot strikers presented shorter duration ground contact times and superior running economy than heel strikers [37]. In the current study, participants wore a prototype shoe that, in in vitro testing, i.e., mechanical testing without participants (Figure 3B), demonstrated approximately 11% greater cushioning than a maximally cushioned shoe, tested under the same conditions [31]. Given the association between footwear geometry and reduced ground contact time [38], as well as the influence of cushioning on leg stiffness and gait adaptations [39,40], such a design may have influenced strike pattern-related spatiotemporal variables. However, no differences were observed in the current dataset, aligning with comparisons between minimalistic and conventional cushioned shoes [8,41]. This supports previous work suggesting strike pattern, rather than shoe condition, has a greater effect on plantar pressures [42]. Further investigation exploring the interaction between shoe geometry, cushioning, and strike pattern is warranted. The absorption phase of ground contact is characterised by impact kinetics, typically determined through force-trace peak identification [5] or a time component (\(<\)0.05 s) and the passive nature of damping [9]. While the first peak is always present in overground running, this criteria is somewhat equivocal during treadmill running [17], where both instrumented-treadmill brand, and kinetic measurement systems, have produced presence and absence of such peaks [15].