## 1 Introduction  
The anterior cruciate ligament (ACL) is one of the key ligaments that stabilize the knee, connecting the femur to the tibia and controlling rotation during flexion and extension [1]. ACL injuries, which manifest as stretching or tearing, are common in sports involving rapid movements, changes in direction, jumps, landings, and indirect or direct trauma to the knee, such as in soccer, basketball, and American football [2; 3; 4; 5; 6]. It has been estimated that the incidence of isolated ACL injuries is approximately 68.6 per 100,000 people per year, but it can reach figures close to 227 per 100,000 in young populations [7; 8]. Among athletes, these numbers are usually higher but vary depending on age, sex, sport, type of exposure, and level of participation [9; 10; 11; 12]. In addition to the functional impact, these injuries entail considerable economic costs, with an estimated USD 17,000 per anterior cruciate ligament reconstruction (ACLR) procedure [13]. In the context of professional sports, particularly in Europe, the incidence of ACL rupture is also significant among elite players, who often return to competition after surgery in relatively short periods, though these vary between leagues. For example, the average time to return to competition after surgery has been reported as 193 days in the French league, while in the English Premier League, it extends to 321 days. In contrast, the Italian, French, and German leagues show a faster recovery compared to the English league [14]. ACLR is considered a fundamental intervention to facilitate a return to sports activity [7; 8; 12; 15]. However, after undergoing ACLR, it is common to observe decreased muscle strength, loss of knee stability, and high pain perception, which can delay the return to sport [16]. In fact, impaired muscle control often persists for up to two years after surgery [17; 18]. Therefore, implementing an efficient rehabilitation process is crucial to reducing the risks associated with ACLR and improving functional outcomes [19; 20]. These limitations have been documented in a recent systematic review, which shows that return-to-sport rates after ACL reconstruction can be as low as 24% [19]. Supporting the shortcomings of traditional rehabilitation approaches, these may be associated with incomplete recovery of muscle strength and neuromuscular control deficits (imbalance between flexors and extensors of the knee) [21; 22], delaying the recovery process and increasing the risk of graft reinjury, additional injuries, and osteearticular pathologies [20; 23]. In this context, one of the proposed methods to optimize conventional rehabilitation is training the muscles of the uninjured limb, a technique known as cross-education (CE) [24]. First described in 1894, cross-education (CE) refers to the phenomenon whereby unilateral strength training induces bilateral neuromuscular adaptations [25]. Recently, CE has gained attention for its potential to preserve strength and promote recovery in various rehabilitation settings [26]. Regarding ACL rehabilitation, CE has demonstrated improvements in strength, kines-thesa, and balance in as little as four weeks, which is relevant since musculoskeletal injuries are associated not only with strength deficits but also with changes in the motor cortex and other brain regions [27; 28]. It is important to note that CE can be implemented through various training modalities, including both isometric and dynamic exercises [29; 30]. In ACLR, it is essential to address not only peripheral changes but also central nervous system alterations. Neuroplasticity, the brain's ability to reorganize in response to external stimuli or structural injuries, plays a key role in this process [31]. In this scenario, CE has shown positive effects by inducing adaptations in the untrained limb through central mechanisms linked to neuroplasticity [32].