Fractal vs Isochronous Cueing in Athletes After ACL Reconstruction

Anterior cruciate ligament (ACL) injuries are among the most prevalent and functionally limiting knee injuries in sports, particularly those that involve pivoting movements. Despite advancements in surgical reconstruction and physical rehabilitation, many athletes continue to exhibit persistent motor control deficits and increased gait variability, both of which are closely linked to a heightened risk of re-injury and long-term joint degeneration. These deficits arise from biomechanical impairments and disrupt proprioceptive input that requires cortical reorganization, contributing to maladaptive neuroplasticity. However, conventional rehabilitation strategies often overlook this neural dimension. Recent findings emphasize the importance of fostering motor variability and promoting neuroplasticity through external focus strategies, including sensorimotor synchronization. While isochronous cues, an invariant stimulus, are commonly used, they do not reflect the natural fluctuations of healthy gait and may reduce its complexity. Fractal-based cues, in contrast, introduce structured variability resembling the natural dynamics of locomotion and have been shown to restore gait complexity in clinical populations. However, no study has yet explored their acute effects on gait variability and corticospinal function following ACL reconstruction (ACLR). This crossover randomized controlled trial aims to compare the acute effects of a single session of treadmill walking synchronized to either fractal or isochronous-based visual cues on gait variability and corticospinal measures in athletes with ACLR. The investigators hypothesize that fractal-based cueing will acutely restore gait variability and enhance corticospinal excitability, evidenced by increased corticospinal excitability and intracortical facilitation, and reduced short-interval intracortical inhibition, thus promoting adaptive neuroplasticity. Conversely, isochronous cueing is expected to maintain or decrease gait complexity without improving corticospinal measures. This study may provide insights that could be highly valuable as a way to promote neuroplasticity and optimize gait rehabilitation after ACLR, also allowing an objective quantification and aiming to restore variability to levels close to those observed in healthy individuals, thus contributing to reducing the re-injury rate.