## 1 Introduction  
The movement of a footballer during a football match is characterized by multidirectional actions [1], which are usually grouped into linear sprints, curvilinear sprints, change of direction, and turns [2, 3]. However, it is difficult to classify the movement of a footballer in a single action. For example, a professional footballer performs a change of direction (COD) at a very high entry speed (\(\sim\)5.5 m/s) [4, 5], and this entry speed is determined by their ability to sprint in line [6]. Therefore, high-speed multidirectional movements are very frequent during a football match (\(\sim\)70%) [4, 5] and are considered decisive in goal situations [7]. Recently, it has been reported that high-speed running actions in La Liga (Spanish top division) are mostly curve sprinting (91.7%) rather than linear (8.3%) [8]. In fact, the scientific literature recognized that they should be included in test batteries for the evaluation of football player performance [2, 9].  
Navicular drop measures excessive pronation [10], as the amount of motion at the subtalar joint can be detected indirectly by measuring the amount of motion at the navicular bone [11]. The navicular drop test measures the distance from the navicular tubercle at its bottom to the ground [12]. In this regard, reduced activation of the intrinsic foot musculature [13] or a fatigued state of the intrinsic foot musculature [14] causes an increase in the navicular drop (i.e., the medial longitudinal arch). This decrease in the positioning of the navicular of the foot influences performance, especially in COD. For example, some authors show that for individuals with flat feet, an effective correction of the alignment of the foot and the temporal parameters of the kinematics of the foot occurred while sprinting or changing direction [15]. This temporary change indicates an improved pulley mechanism thanks to the navicular height reaching its minimum value. Therefore, good intrinsic foot muscle activation seems to be crucial for better shock absorption and improving multidirectional speed abilities [16].  
Using elastic bands as a training mode has been a growing trend, as they have shown similar strength and power improvements to traditional resistance training [17; 18]. One of their main advantages is adapting the force vector or movement plane where the force is applied, respecting the dynamic correspondence with sports movements [19]. High-intensity action performances such as COD and curve-sprinting abilities mainly depend on applying force in a lateral position [2]. As we have seen in non-published pilot studies, a lateral-step movement using a lateral and low force vector through an elastic band increases the intrinsic foot muscle activation measured through electromyography. However, no study in the literature has analyzed the effect of a lateral-step exercise using elastic bands on multidirectional sprinting abilities. Thus, the main aims of the current study were (1) to assess the effect of including the lateral-step or sidestep exercise with elastic bands on multidirectional speed abilities (linear, COD, and curve sprinting) and navicular drop, and (2) to know the impact of navicular drop changes on multidirectional sprinting changes in young male football players.