## 4 Discussion
The present results may also suggest that the dampening effect specifically associated with the FFS alone was probably underestimated in the studies on foot strike pattern cited above. The question arises as to why centre of mass braking is attenuated under the FFS condition compared to the RFS condition. To interpret this finding, it should be stressed that this braking has an energetic and attentional cost [14; 15] and shares a dampening action on collision forces with the foot strike strategy. Therefore, when the FFS pattern is employed, the need to actively brake the centre of mass fall becomes less crucial than when the RFS pattern is used. The CNS would then attenuate this active brake in order to minimise the associated energetic and attentional cost, and would rely more heavily on the efficiency of the foot strike strategy to dampen the collision forces. This implies that the CNS takes into account the foot strike pattern and the related dampening effect when programming braking force generation. This statement is in line with the hypothesis of an interdependent relationship between these two mechanisms (active braking and foot strike pattern) for optimal stability control and better ground reaction force management. The results linking ML APAs to the foot strike pattern further strengthen this hypothesis (paragraph below). During gait initiation or any locomotor task, imbalance occurs in the frontal plane due to the transition from a bipedal to a unipedal stance. Following swing foot-off, the centre of mass fallsrapidly towards the swing leg side under gravity, and this lateral fall is braked by foot contact with the ground. This ML imbalance is greater when an obstacle is to be cleared, since the duration of the lateral fall of the centre of mass is increased compared to a control condition with no obstacle to be cleared [10; 11; 31; 32; 33]. The development of ML APAs is therefore of utmost importance to maintain stability as it acts to minimise this lateral fall by propelling the centre of mass towards the stance leg side and thus attenuating the ML gap between the centre of mass and the centre of pressure at the time of swing foot-off [7; 8; 10; 11; 34; 35]. Previous modelling studies demonstrated the link between ML APAs and ML stability at foot contact [8; 10; 11; 34]. In the present study, the results showed that the amplitude of these ML APAs, in terms of peak centre of pressure shift, was lower under the FFS than under the RFS condition (\(\Delta=9.4\%\)). It also revealed that this lower amplitude was not accompanied by a ML APA duration lengthening strategy. Such a trade-off strategy between APA amplitude and APA duration has been repeatedly reported in the literature under various conditions of postural constraints, such as fear of falling [36], fatigue [37; 38; 39], leg dominance [40] and temporal pressure [41]. There was no such compensating trade-off strategy in the present study. Consequently, the ML centre of mass velocity at the time of swing foot-off, which represents the total amount of forces applied to the centre of mass during the APAs, reached a lower value under the FFS than under the RFS condition (\(\Delta=5.99\%\)). For the above reasons, ML dynamic stability, as measured with the MOS [25], could be expected to be lower under the FFS than under the RFS condition. However, contrary to this expectation, the MOS reached much higher values under the FFS than under the RFS condition (\(\Delta=71.42\%\)), that is, ML dynamic stability was significantly improved. Changes in two components of the MOS with the foot strike strategy can account for this result, as detailed below. First, the ML centre of mass velocity at the time of foot contact reached a lower value under the FFS than under the RFS condition (\(\Delta=14\%\)), that is, the velocity at which the centre of mass fell towards the swing leg side was attenuated.