## 1 Introduction  
Scientific evidence highlights the critical role of appropriate knee extension (KE) and flexion (KF) force in both performance enhancement [1] and injury prevention [2] among young soccer players. Adequate knee extension strength is crucial for generating power during activities such as sprinting, jumping, and kicking, thereby enhancing athletic performance on the field [3]. Conversely, insufficient strength in knee flexors and extensors can increase the risk of injury, particularly to the anterior cruciate ligament, a common injury in soccer [4]. Research indicates that targeted strength training programs focusing on improving knee extension and flexion can significantly reduce the incidence of anterior cruciate ligament injuries in young athletes. Furthermore, maintaining a balance between these muscle groups is essential for promoting biomechanical efficiency and reducing the strain on the knee joint during dynamic movements [5], ultimately contributing to both performance optimization and injury prevention in youth soccer. Improving muscle performance through warm-up strategies can significantly enhance the athletic readiness of participants and potentially reduce the risk of injury [6]. Various warm-up techniques have been shown to enhance proprioception and joint stability, which are vital in preventing non-contact injuries, particularly those affecting knee ligaments [7]. Including exercises that target the quadriceps, hamstrings, and hip muscles during warm-ups can optimize knee joint mechanics and alignment, thereby further decreasing the likelihood of overuse injuries throughout the season [8]. By following evidence-based warm-up protocols [9], coaches and players can actively reduce knee-related risks, promoting safer and more effective participation in soccer activities. Among other strategies, diagonal manual mobilization (DM) can effectively enhance immediate strength and readiness in young football players, albeit through different mechanisms [10]. DM techniques, involving manual manipulation of the lower limb joints, have been shown to increase joint range of motion, proprioception, and neuromuscular excitability, potentially priming the muscles for improved performance [11]. In previous research involving young soccer athletes, the application of tissue mobilization emerged as a significant contributor to enhancing various aspects of athletic performance [12]. Findings revealed a reduction in fatigue alongside significant enhancements in fitness levels and muscular power [12]. Within the experimental cohort, which underwent soft tissue mobilization, marked improvements in knee extension and flexion were observed, particularly at speeds of 60 and 180 \({}^{\circ}\)/s [12]. Further reinforcing these outcomes, research conducted by [PERSON] et al. [10] highlighted the efficacy of manual therapies directed towards the posterior high muscles. Through interventions such as manual massage and muscle energy techniques, participants exhibited enhanced performance in the ten-repetition maximum test, showcasing increased maximal load lifts [10]. However, despite these advancements, a notable research gap remains, as evidenced by the study conducted by [PERSON] and [PERSON] [13], which primarily explored the effects of mobilization on KE strength. This highlights the need for further investigation into the impacts of low-velocity diagonal mobilization on both knee flexors and extensors, particularly within the context of healthy soccer players. While DM shows promise, it has not been tested against many other popular strategies. Although not specifically designed to elicit acute responses, but rather as a chronic adaptation, Nordic curl exercises directly target the hamstring muscles, possibly enhancing eccentric strength and muscle activation [14]. Studies have demonstrated that performing eccentric exercises like the Nordic curl can increase muscle activation and potentiate subsequent muscle contractions [15].