## 1 Introduction  
The footstrike pattern of runners has received much attention in the past decade, particularly the differences between rearfoot strike (RFS) and midfoot or forefoot strike (FFS). This increasing interest in footstrike patterns can be justified by the possible associations with running-related injuries [1; 2; 3; 4]. In particular, FFS has been found to be associated with the attenuation of the lower limbs loads, which helps to reduce the incidence of running-related injuries [4; 5]. However, RFS mitigates part of the Achilles tendon loading rate the foot is accountable for, especially in early stance [3]. The effect of striking patterns on lower limb joint kinetics and kinematics has thus far been reported, while foot joint and segment kinematics have rarely been investigated and in a limited number of foot joints and segments only [6; 7; 8; 9]. Lower limb kinematics showed that FFS presents the foot angle at initial contact in a plantar flexed position and RFS in dorsiflexed position [10]. In addition, FFS runners contact the ground with greater knee flexion compared to RFS runners [10]. Kinematic differences have also been reported in the frontal plane, where greater rearfoot version is observed in FFS compared to RFS [10]. Two recent studies used multi-segment foot models to investigate and compare kinematic patterns in RFS or FFS running. [PERSON] et al. [7] analyzed the influence of the foot strike technique on medial longitudinal arch mechanics and intrinsic foot muscle function during running. As expected, it was observed that midfoot and rearfoot joint angles of FFS runners were more plantar flexed at footstrike, the rearfoot was less dorsiflexed at mid-stance, and there was more ankle plantarflexion at toe-off compared to the RFS runners. In addition, FFS runners presented a larger loading on the midfoot, which was associated with greater intrinsic foot muscles activation, probably to increase elastic energy storage and return while preventing excessive midfoot deformation. In this study, however, only 13 runners were assessed, and no objective measure was used to determine the runners striking patterns. In fact, runners were instructed to run using an FFS pattern, even if this was not their typical striking pattern. The other study, conducted by [PERSON] et al. [9], showed that during loading response, the ankle is more plantar flexed, inverted, and adducted in FFS compared to RFS. The midtarsal joint is less inverted and less adducted at initial contact in FFS. During the early stance, the midtarsal has a greater dorsiflexion range and reduced abduction excursion. During the loading phase, the midtarsal is more inverted in FFS and more exerted in RFS. The midtarsal joint increases the plantarflexion excursion at late stance in FFS. Finally, the metatarsophalangeal joints are less plantarflexed at early stance, and the dorsiflexion range increases during late stance. However, in this study, the participants were not habitually FFS or RFS, and the authors did not control for potential adaptations that may occur due to the conversion of the footstrike pattern during the data collection session. We propose another way of analyzing the foot kinematic without immediately resorting to reductionism of variables, analyzing the whole time series using a functional data analysis, instead of a collection of discrete variables within a time series. In this study, we focus on improving our understanding on the effects of the striking pattern on foot kinematics by using a validated multi-segment foot model applied on a large population of naturally RFS and FFS runners. The present results may contribute to further expand our comprehension of the relationships between foot function and running-related injuries, as there are differences in type of injuries reported in FFS and RFS. For example, posterior lower leg injuries are reported for FFS and repetitive stress injuries are reported in RFS [3; 4; 5].