## 1 Introduction  
Rhythmic gymnastics is a discipline that demands a high level of flexibility, strength, and explosive power, particularly in jumping performance. Among the key assessments of lower limb power in gymnasts is the countermovement jump (CMJ) test, which evaluates the stretch-shortening cycle's efficiency and neuromuscular activation [1,2]. However, rhythmic gymnasts frequently experience low back pain (LBP) due to the extreme range of motion required in their sport, along with repetitive spinal hyperextension and postural imbalances, which might compromise jump performance [3]. Addressing LBP in gymnasts necessitates specialized postural correction methods.  
Among the various postural rehabilitation techniques, the Mezieres method and Isostretching have gained prominence in the treatment of LBP in elite athletes, including rhythmic gymnasts [4,5]. The Mezieres method is based on the principle of global postural re-education, emphasizing the elongation of muscular chains to correct postural asymmetries and reduce musculoskeletal discomfort [6]. Recent studies have demonstrated its effectiveness in improving flexibility and reducing pain in athletes, contributing to enhanced motor performance and postural stability [3,4]. Similarly, Isostretching is a corrective exercise approach that integrates isometric muscle activation with controlled breathing, promoting spinal alignment and core stability [5,7]. This method has been shown to alleviate chronic low back pain while enhancing flexibility and neuromuscular coordination [8,9].  
While extensive research has examined the effects of dynamic and static stretching on jump performance, the influence of long-term postural therapy techniques on explosive movements such as CMJ remains largely unexplored. Moreover, traditional acute interventions, such as post-activation potentiation (PAP) and dynamic stretching, have demonstrated short-term improvements in jumping ability, but their long-term benefits in athletes with postural dysfunctions or chronic pain remain uncertain [10,11,12]. In rhythmic gymnasts, previous studies have highlighted the effectiveness of Mezieres and Isostretching methods in improving postural alignment, flexibility, and neuromuscular coordination [4,5], suggesting their potential role in optimizing movement patterns and motor control. However, to the best of our knowledge, no study has directly analyzed the impact of these methods on explosive strength performance in rhythmic gymnasts with LBP. Given that proper postural control influences force transmission and biomechanical efficiency during jump execution [13], understanding the role of postural rehabilitation techniques in CMJ performance could provide valuable insights into injury prevention and athletic performance enhancement.  
Therefore, we aim to analyze the impact of the Mezieres method and Isostretching on CMJ performance in rhythmic gymnasts with LBP, which might contribute to the development of evidence-based rehabilitation protocols that balance postural correction with athletic performance optimization. Specifically, it aims to investigate the influence of the Mezieres method and Isostretching on CMJ performance in rhythmic gymnasts with LBP, evaluating changes in jump height, movement efficiency, and pain perception. The findings will contribute to the development of evidence-based rehabilitation protocols that balance postural correction with athletic performance optimization.