## 1 Introduction  
Team sports often involve intermittent, high-intensity activity combined with periods of lower-intensity movement, requiring athletes to be versatile and dynamic in their physical, tactical, and technical roles [1]. These sports, which frequently feature 70 to 90 min matches, are typically played by teams of varying sizes, including a mix of goalkeepers and outfield players [2]. In many team sports, sprinting is a critical component of performance. Speed and acceleration are key attributes that can influence both offensive and defensive outcomes. For example, rapid acceleration over short distances, such as 20 m, often proves decisive in gaining possession, executing attacks, or neutralising threats [3, 4]. Elite players can engage in high-intensity actions every 20 to 30 s, leading to numerous sprints and accelerations throughout the game [5]. Consequently, the ability to accelerate quickly is a vital skill that can determine the success of individual plays and, ultimately, the overall outcome of the match. As a result, developing the physical qualities that enhance sprint performance is of significant interest to athletes and coaches in team sports, as these attributes can be crucial for achieving success on the field [6]. Sprinting is frequently described by step kinematics. Step length is the distance between alternating contacts of each foot, step frequency is the rate at which steps can be reproduced, and ground contact time (GCT) is the duration of time when the leg is in contact with the ground and flight time is the period when the athlete is airborne. Sprinting velocity is the product of step length and step frequency [7]. Improving sprint performance requires an increase in step length, step frequency, or both [4]. A high step length [8] and frequency [6; 9] are important for acceleration. Further, lower GCTs are associated with efficient acceleration [6; 9]. The ground contact phase of sprint acceleration is considered a fast stretch shortening cycle (SSC) activity with force expressed maximally in GCTs of <0.25 s [10] under the commonly reported threshold for fast versus slow SSC actions [11]. Therefore, acceleration capacity requires an ability to develop force in short time periods via the fast SSC and is influenced by specific strength and power capacities [6]. It has been postulated that reactive strength is a physical quality that influences acceleration and overall sprint performance [3; 6]. The stretch shortening cycle (SSC) plays a crucial role in sprint acceleration by enhancing force production through the rapid transition from eccentric to concentric muscle actions [12]. In the initial stages of acceleration, GCTs are relatively long (~200 ms), providing more time for force development through a slower, force-dominant SSC [13; 14]. During this phase, athletes generate high horizontal ground reaction forces (GRFs), which are essential for overcoming inertia and driving forward propulsion [13]. These forces are characterised by strong horizontal braking-propulsive impulse, emphasising the importance of horizontally directed force application in the early strides [15]. As acceleration progresses and velocity increases, GCTs decrease substantially (~120-140 ms), limiting the window for force application. To remain effective under these time constraints, the SSC must function more rapidly, relying on increased muscle-tendon stiffness, preactivation, and efficient elastic energy utilisation [16; 17]. Consequently, the orientation of GRFs gradually shifts from horizontal to vertical, reflecting a biomechanical transition from force production to velocity maintenance and increased stride frequency [3; 18]. In the later stages of acceleration, fast SSC characteristics--such as shorter GCTs, minimised joint displacement, and efficient stiffness regulation--become critical for sustaining high stride rates. Importantly, reducing braking forces during this phase has emerged as a key performance determinant.