## 1 Introduction  
Symmetry plays a pivotal role in sports training, particularly in sports that require repetitive, cyclical movements such as swimming, running, and rowing [1; 2; 3]. Symmetrical athletes regularly demonstrate an exact correspondence of size, shape and actions when those are split along a given axis [4]. An athlete's ability to generate force and maintain balance between the left and right sides of the body can significantly influence their efficiency, speed and endurance [5]. Although it has been argued that sport coaches and athletes should not look for perfect symmetry [6], the early detection of exaggerated asymmetries in cyclical sports may allow for targeted interventions, helping to improve movement quality.  
Swimming is a cyclical and complex sport that requires a combination of technique, endurance and strength [7]. Symmetry in swimming refers to the balance between the left and right sides of the body during a specific movement and can be computed using swimming cycle kinematics [8], in-water forces during tethered [9] or free swimming [10] and using dryland strength ratios [11]. Asymmetries, whether in technique or muscle strength, can reduce propulsion [12], while proper bilateral coordination in force application ensures that swimmers can efficiently transfer force from their body to the water [13] and maintain velocity at desired levels [14]. Although studies reported that asymmetries rarely impact swimming performance [15], a crucial aspect of a swimmer's development is ensuring that technical skills and the physical strength of both sides of the body progress in harmony over time [16].  
The performance enhancement in young swimmers involves balancing both in-water and dryland characteristics [17], which can be modulated as the competitive season occurs. Coaches often use in-water and dryland strength routines throughout a full competitive season (according to each training macrocycle) to improve the swimmer's strength capacity [18]. These kind of strategies are sequentially implemented as the training macrocycle progresses and can be rescheduled according to the swimmer's response to training. In fact, the training interventions can trigger small to moderate reductions in interlimb asymmetries from pre- to post-training programs [19]. So, the changes that may happen across a training macrocycle may highlight the physical adaptations taking place as a result of training and model the degree of symmetry in both in-water and dryland environments.  
The training intervention studies focusing on symmetry in swimming are few and showed mixed findings. Unhanged symmetry values were found in adolescent swimmers after 12 weeks of training in two sequential competitive seasons [20]. On the other hand, young swimmers became more asymmetrical at the end of one competitive season without any impact on swimming performance [21]. Given this uncertainty, additional studies on symmetry in both in-water and dryland environments are needed. This is particularly important at younger ages as these are swimmers who are refining their technique while growing. So, an early detection of exaggerated imbalances can inform coaches of the necessary training adjustments in the search for the optimal dose-response relationship.  
This study aimed to accomplish the following: (i) monitor the in-water and dryland interlimb asymmetry of young competitive swimmers throughout a full training macrocycle; and (ii) verify the associations between symmetry or related variables with performance and its impact at each time point of the macrocycle. It was hypothesized that (i) swimmers would remain asymmetrical in both in-water and on dryland after the training macrocycle; and (ii) there would be no associations between symmetry and performance in both time points without a negative impact on performance.