## 1 Introduction  
Like all terrestrial species, humans move in a gravity field that permanently attracts them towards the centre of the earth. Therefore, balance control is a key component of daily motor tasks. Gait initiation (GI), which corresponds to the transient phase between quiet standing and level walking, is a classical paradigm for investigating how balance is controlled during a functional whole-body movement [1, 2]. Gait initiation can be broken down into a postural phase (corresponding to anticipatory postural adjustments (APAs)), followed by a swing phase that ends at the time of swing foot contact with the support surface. These APAs are characterised by a centre of pressure (COP) shift backwards towards the heels, and laterally towards the forthcoming swing leg. The backward centre of pressure shift reflects a strategy to generate the initial propulsive forces necessary to reach the intended centre of mass velocity at the end of gait initiation [3, 4, 5, 6]. The mediolateral (ML) centre of pressure shift reflects a strategy to propel the centre of mass above (or beneath) the forthcoming stance foot in order to maintain ML stability during the swing phase of gait initiation [7, 8, 9, 10, 11]. Besides ML APAs, a major mechanism involved in stability control is the braking of the centre of mass fall during the swing phase of gait initiation. Previous lines of research have shown that braking is an active phenomenon that occurs in anticipation of the swing foot's collision with the ground, and involves the activation of the soleus of the stance leg [12; 13; 14; 15]. Anticipatory centre of mass braking attenuates the vertical ground reaction forces (GRFs) at the time of foot collision (hereafter called collision forces), thus facilitating balance control and reducing the risk of injury linked to the transmission of this impact throughout the musculoskeletal system. These collision forces are also known to depend on the swing-foot strike pattern at the time of collision [16; 17; 18]. At least two main swing-foot strike patterns have been identified in the literature--rearfoot strike (RFS), where the swing heel strikes the ground first, and forefoot strike (FFS), where the swing toe strikes the ground first [16]. Because studies have reported that participants systematically used an RFS pattern, foot strike patterns have so far not been considered in the literature on gait initiation. However, a recent study showed that when gait was initiated with the goal of clearing an obstacle longer than 30% of body height, a change from an RFS to an FFS pattern was observed in most trials [10]. Based on previous research on the effect of the foot strike pattern on collision forces during stepping down while walking [17; 18] or running [16; 19; 20; 21; 22], it was proposed that this change in foot strike pattern reflected a strategy directed at attenuating collision forces. It is surprising that the authors of these important lines of research, focusing on foot strike pattern effects, did not consider that the magnitude of the anticipatory braking might have changed between the RFS and FFS patterns. Indeed, such a change could at least partly account for the differences in the collision forces observed, with a larger anticipatory centre of mass brake being potentially responsible for greater attenuation of the collision forces. More generally, a brief literature review shows that the balance control mechanisms described above have been investigated by independent lines of research (for a recent review see [2]). Thus, it remains largely unknown whether these mechanisms (i.e., ML APAs, force braking and foot strike pattern) are independently controlled by the central nervous system (CNS) or are interdependent. Gait initiation with an obstacle to be cleared is a natural task that offers the opportunity to test the interdependence between these mechanisms since, as stated above, both foot strategies are naturally used to land on the support surface.