Fractal vs Isochronous Cueing in Athletes After ACL Reconstruction

Study Results

Results pending

The study team has not published outcome measurements, participant flow, or safety data for this trial yet. Check back later for updates.

Basic Information

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Recruitment Status

RECRUITING

Clinical Phase

NA

Total Enrollment

36 participants

Study Classification

INTERVENTIONAL

Study Start Date

2025-10-03

Study Completion Date

2026-02-28

Brief Summary

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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.

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Detailed Description

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This study will test a laboratory-based intervention using gait trials with sensorimotor synchronization, a common approach in gait rehabilitation aimed at restoring or acutely modifying gait variability. The intervention, called SyncGait, consists of treadmill walking synchronized with visual cues. Following a crossover design, each participant will complete two sessions, one with fractal cueing (FRC) and one with isochronous cueing (ISO), with the order randomized. Each cued trial will last 12 minutes and will be preceded and followed by uncued walking trials. The visual cues will be presented as a moving bar on a screen positioned in front of the treadmill. For the FRC condition, the cues will be individualized to each participant's stride time variability, generated through a fractal algorithm and validated using detrended fluctuation analysis. For the ISO condition, cues will match each participant's average stride time without variability. Participants will be instructed to synchronize heel strikes of the reconstructed limb with the top of the moving bar. The treadmill (Bertec Inc., USA) will record gait data at 1000 Hz. Each session will be conducted individually, supervised by at least two trained team members. A sample size of 36 participants was determined to ensure adequate power (90%) to detect a moderate effect size (ηp² = 0.25) at a 5% significance level, accounting for an anticipated 20% dropout rate. To encourage participation and retention, participants will receive a personalized evaluation report and a free isokinetic assessment within 12 months. Data collection will include both gait and corticospinal outcomes. Gait variability will be analyzed from treadmill force data, focusing on stride intervals and synchronization performance. Corticospinal outcomes will be assessed using transcranial magnetic stimulation (TMS) with a BiStim2 stimulator (Magstim®, UK). Electromyography (Delsys Trigno, AD Instruments, NZ) will be recorded from quadriceps and hamstrings, while knee strength will be assessed with an isokinetic dynamometer (Humac Norm, USA). Standardized electrode placement and contraction protocols will ensure reproducibility. During testing, single- and paired-pulse TMS protocols will be applied at 10% of maximal voluntary contraction. Ten stimuli per condition will be collected, providing reliable estimates of excitability and inhibition. Visual feedback will help participants maintain the required contraction level throughout assessments. Statistical analysis will begin with normality testing (Shapiro-Wilk). Linear mixed models (Time × Cue condition) will be used for primary and secondary outcomes. Post-hoc comparisons will use Bonferroni corrections. Synchronization accuracy will be compared with paired t-tests. Statistical significance will be set at p \< 0.05, and analyses will be performed using Jamovi software. This protocol is designed to rigorously test whether fractal cueing can restore healthy gait variability patterns and enhance corticospinal excitability in athletes with ACL reconstruction, compared with conventional isochronous cueing.

Conditions

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Anterior Cruciate Ligament Reconstruction Anterior Cruciate Ligament Reconstruction Rehabilitation Athlete

Study Design

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Allocation Method

RANDOMIZED

Intervention Model

CROSSOVER

This study is a crossover randomized controlled trial, comprising two sessions. Each session will take approximately 2 hours, and the sessions will be separated from 7 to 10 days. Both sessions will be held at the same period of the day to avoid the circadian effect on our primary outcome. The two sessions will be similar. At the beginning of the first session, however, three questionnaires will be administered to collect the demographic and baseline characteristics of the participants. Following the completion of these questionnaires, a randomization process through a fixed block method will be conducted by the study's supervisor to determine the order in which the intervention will be presented across the two sessions. The participants will be asked to complete three 12-minute gait trials in each session: one cued trial and two uncued trials. A minimum of 20 minutes of rest will be taken between each trial while collecting the cortical drive assessment, PRE and POST the cued trial.

Primary Study Purpose

BASIC_SCIENCE

Blinding Strategy

DOUBLE

Participants Outcome Assessors

The randomized order will be transmitted only to the main researcher through a sealed envelope. Participants will be blinded throughout their participation. Importantly, the participants are unable to detect the subtle changes in variability between the Isochronous and Fractal cueing conditions. The main researcher will not be blinded for the condition given the necessity to program the metronome per session. However, the remaining team will be blinded and, therefore, will run the data analysis.

Study Groups

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Fractal Cueing, Then Isochronous Cueing

Participants exposed to 12-minute treadmill walking synchronized to a visual fractal metronome individualized to stride time variability. After a washout period of 1 week, participants will be exposed to 12-minute treadmill walking synchronized to a visual isochronous metronome with fixed stride time.

Group Type EXPERIMENTAL

Fractal Cueing

Intervention Type DEVICE

Walking synchronized to a visual fractal metronome.

Isochronous Cueing

Intervention Type DEVICE

Walking synchronized to a visual Isochronous metronome.

Isochronous Cueing, then Fractal cueing

Participants exposed to 12-minute treadmill walking synchronized to a visual isochronous metronome with fixed stride time. After a washout period of 1 week, participants will be exposed to 12-minute treadmill walking synchronized to a visual fractal metronome individualized to stride time variability.

Group Type EXPERIMENTAL

Fractal Cueing

Intervention Type DEVICE

Walking synchronized to a visual fractal metronome.

Isochronous Cueing

Intervention Type DEVICE

Walking synchronized to a visual Isochronous metronome.

Interventions

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Fractal Cueing

Walking synchronized to a visual fractal metronome.

Intervention Type DEVICE

Isochronous Cueing

Walking synchronized to a visual Isochronous metronome.

Intervention Type DEVICE

Eligibility Criteria

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Inclusion Criteria

* Undergone unilateral ACL reconstruction less than 2 years ago;
* Have medical release for the full load on the injury limb for at least 2 weeks;
* Be independently pain-free walking;
* Being sports athletes according to an athlete description: Training regularly to improve performance, actively participating in competitions or formally registering in a sports federation or association;
* Must be able to understand and perform the requested task.

Exclusion Criteria

* Participants with previous surgery on either knee;
* Those with more than 3 months between ACL injury and surgery;
* More than 2 weeks between surgery and the start of physical therapy;
* Had another musculoskeletal injury in the lower limb within the past 6 months;
* Another musculoskeletal surgery within the past 18 months;
* Participants with a history of movement system pathologies, such as nervous system, cardiovascular, pulmonary, integumentary, or endocrine conditions;
* Participants with vestibular or somatosensory system pathologies or visual impairments limiting their ability to see the metronome required for the task;
* Use of medications that could affect locomotion and balance.

Minimum Eligible Age

15 Years

Maximum Eligible Age

35 Years

Eligible Sex

ALL

Accepts Healthy Volunteers

No