Fractal vs Isochronous Cueing in Athletes After ACL Reconstruction (SyncGait)

November 17, 2025 updated by: Egas Moniz - Cooperativa de Ensino Superior, CRL

Comparison Between a Session of Walking Synchronized to Fractal- VS Isochronous-Based Cues on Gait Variability and Corticospinal Measures in Athletes With a Reconstructed Anterior Cruciate Ligament: A Crossover Randomized Controlled Trial

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.

Study Overview

Status

Status

Indicates the current recruitment status or the expanded access status.
Recruiting

Conditions

Conditions

The disease, disorder, syndrome, illness, or injury that is being studied. On ClinicalTrials.gov, conditions may also include other health-related issues, such as lifespan, quality of life, and health risks.

Intervention / Treatment

Intervention / Treatment

A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.

Detailed Description

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.

Study Type

Study Type

Describes the nature of a clinical study. Study types include interventional studies (also called clinical trials), observational studies (including patient registries), and expanded access.
Interventional

Enrollment (Estimated)

Enrollment

The number of participants in a clinical study. The "anticipated" enrollment is the target number of participants that the researchers need for the study.
36

Phase

Phase

The stage of a clinical trial studying a drug or biological product, based on definitions developed by the U.S. Food and Drug Administration (FDA). The phase is based on the study's objective, the number of participants, and other characteristics. There are five phases: Early Phase 1 (formerly listed as Phase 0), Phase 1, Phase 2, Phase 3, and Phase 4. Not Applicable is used to describe trials without FDA-defined phases, including trials of devices or behavioral interventions.
  • Not Applicable

Contacts and Locations

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Study Contact

Study Contact

The name and contact information for the person who can answer enrollment questions for a clinical study. Each location where the study is being conducted may also have a specific contact, who may be better able to answer those questions.

Study Contact Backup

Study Locations

  • Portugal
    • Monte de Caparica
      • Almada, Monte de Caparica, Portugal, 2829-511

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Eligibility Criteria

The key requirements that people who want to participate in a clinical study must meet or the characteristics they must have. Eligibility criteria consist of both inclusion criteria (which are required for a person to participate in the study) and exclusion criteria (which prevent a person from participating). Types of eligibility criteria include whether a study accepts healthy volunteers, has age or age group requirements, or is limited by sex.

Ages Eligible for Study

  • Child
  • Adult

Accepts Healthy Volunteers

No

Description

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.

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Basic Science
  • Allocation: Randomized
  • Interventional Model: Crossover Assignment
  • Masking: Double

Arms and Interventions

Participant Group / Arm

Participant Group / Arm

A group or subgroup of participants in a clinical trial that receives a specific intervention/treatment, or no intervention, according to the trial's protocol.
Intervention / Treatment

Intervention / Treatment

A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.
Experimental: 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.
Device: Fractal Cueing
Walking synchronized to a visual fractal metronome.
Device: Isochronous Cueing
Walking synchronized to a visual Isochronous metronome.
Experimental: 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.
Device: Fractal Cueing
Walking synchronized to a visual fractal metronome.
Device: Isochronous Cueing
Walking synchronized to a visual Isochronous metronome.

What is the study measuring?

Primary Outcome Measures

Primary Outcome Measures

In a clinical study's protocol, the planned outcome measure that is the most important for evaluating the effect of an intervention/treatment. Most clinical studies have one primary outcome measure, but some have more than one.
Outcome Measure
Measure Description
Time Frame
Gait Variability Measured by Fractal Scaling Exponent of inter-stride intervals
Time Frame: Pre- (40 minutes before) and Post- (40 minutes after) -Intervention
The fractal-scaling exponent, α, of inter-stride intervals (α-ISIs) will be determine by calculating the time between two consecutive heel strikes of the same foot. First, the investigators will identify the heel strike events of the dominant foot. To improve the identification of this event, the signals will be filtered using a 2nd order, zero lag low-pass Butterworth filter with a cutoff frequency of 20 Hz. Then, Detrended Fluctuation Analysis (DFA) will be used to determine the fractal-scaling, an index of complexity. The DFA is a modified random-walk analysis that makes use of a long-range correlated time series. The long-range correlation can be mapped to self-similar calculations through simple integration.
Pre- (40 minutes before) and Post- (40 minutes after) -Intervention
Corticospinal Excitability Measured by Motor Evoked Potential Amplitude
Time Frame: Baseline (Pre) and immediately after the intervention (Post)
Conducted using Spike2 software (version 10; Cambridge Electronic Design, Cambridge, United Kingdom) and subsequently exported to, MATLAB R2018a (The MathWorks, Natick, Massachusetts, United States) for processing and analysis. Corticospinal Excitability will be quantified as the peak-to-peak amplitude of MEPs elicited by a single-pulse TMS stimulus, with values averaged across 10 trials per participant.
Baseline (Pre) and immediately after the intervention (Post)
Cortical Silent Period (SP) Duration
Time Frame: Baseline (Pre) and immediately after the intervention (Post)
Silent period will be calculated as the time from MEP onset to the resumption of voluntary EMG activity, expressed as SP = resumption of voluntary EMG time - MEP onset (58), and averaged across all 10 stimuli.
Baseline (Pre) and immediately after the intervention (Post)
Intracortical Facilitation (ICF)
Time Frame: Baseline (Pre) and immediately after the intervention (Post)
ICF will be determined using the same calculation method but with an interstimulus interval of 12 ms (ICF = conditioned MEP / control MEP).
Baseline (Pre) and immediately after the intervention (Post)
Short-Interval Intracortical Inhibition (SICI)
Time Frame: Baseline (Pre) and immediately after the intervention (Post)
SICI will be calculated as the ratio between the conditioned MEP elicited with a paired-pulse TMS protocol (interstimulus interval: 3 ms) and a control MEP obtained from AMT assessment, expressed as SICI = conditioned MEP / control MEP.
Baseline (Pre) and immediately after the intervention (Post)

Secondary Outcome Measures

Secondary Outcome Measures

In a clinical study's protocol, a planned outcome measure that is not as important as the primary outcome measure for evaluating the effect of an intervention but is still of interest. Most clinical studies have more than one secondary outcome measure.
Outcome Measure
Measure Description
Time Frame
Magnitude of variability
Time Frame: Pre- (40 minutes before) and Post- (40 minutes after) -Intervention
Calculate the coefficient of variation of inter-stride intervals, representing the magnitude of variability.
Pre- (40 minutes before) and Post- (40 minutes after) -Intervention
Synchronization Accuracy
Time Frame: During Intervention
Asynchronies (ASYNC), i.e., the time difference between the heel strikes and the cues, expressed in milliseconds. This will be used to ensure that differences at the primary outcome are not the result of different synchronization performances. A negative value of ASYNC indicates that the heel strike occurred before the cue. The ASYNC provides information regarding the strategies used and the performance of the synching processes, serving as a control parameter to reliably interpret our results in terms of gait complex.
During Intervention

Other Outcome Measures

Other Outcome Measures

For clinical trials, a planned measurement described in the protocol that is used to determine the effect of an intervention/treatment on participants. For observational studies, a measurement or observation that is used to describe patterns of diseases or traits, or associations with exposures, risk factors, or treatment. Types of outcome measures include primary outcome measure and secondary outcome measure.
Outcome Measure
Measure Description
Time Frame
Demographic characterization of the sample by Lysholm Knee Score (LKS).
Time Frame: At the beginning of the first session (Day 1)
The LKS show good internal consistency (Cronbach's α = 0.802) and high test-retest reliability (ICC = 0.859). The LKS consists of 8 items with 3 to 6 closed-response options, assessing knee function aspects such as pain, swelling, locking, and instability. The scale is completed in ≈5 minutes, with higher scores indicating better knee function.
At the beginning of the first session (Day 1)
Demographic characterization of the sample by Tegner Activity Scale (TAS)
Time Frame: At the beginning of the first session (Day 1)
The TAS show good internal consistency (Cronbach's α = 0.802) and high test-retest reliability (ICC = 0.972). The TAS comprises a single item with 11 activity levels (0-10), reflecting increasing physical demand. The scale is completed in ≈2 minutes, with higher scores indicating greater physical activity levels (TAS).
At the beginning of the first session (Day 1)
Demographic characterization of the sample by Tampa Scale of Kinesiophobia (TSK)
Time Frame: At the beginning of the first session (Day 1)
The TSK consists of 13 items rated on a 4-point Likert scale (1 = strongly disagree to 4 = strongly agree), with a total score ranging from 13 to 52, where higher scores indicate greater kinesiophobia. It required 4 to 6 minutes to complete the instrument and demonstrated good internal consistency (α = 0.82) and test-retest reliability (ICC = 0.99), confirming its reliability for assessing kinesiophobia.
At the beginning of the first session (Day 1)

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Sponsor

The organization or person who initiates the study and who has authority and control over the study.
Egas Moniz - Cooperativa de Ensino Superior, CRL

Investigators

Investigators

A researcher involved in a clinical study. Related terms include site principal investigator, site sub-investigator, study chair, study director, and study principal investigator.
  • Study Director: João R Vaz, PhD, Egas Moniz School of Health & Science

Publications and helpful links

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General Publications

Study record dates

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Study Major Dates

Study Start (Actual)

Study Start

The actual date on which the first participant was enrolled in a clinical study. The "anticipated" study start date is the date that the researchers think will be the study start date.
October 3, 2025

Primary Completion (Estimated)

Primary Completion

The date on which the last participant in a clinical study was examined or received an intervention to collect final data for the primary outcome measure. Whether the clinical study ended according to the protocol or was terminated does not affect this date. For clinical studies with more than one primary outcome measure with different completion dates, this term refers to the date on which data collection is completed for all the primary outcome measures. The "anticipated" primary completion date is the date that the researchers think will be the primary completion date for the study.
February 1, 2026

Study Completion (Estimated)

Study Completion

The date on which the last participant in a clinical study was examined or received an intervention/treatment to collect final data for the primary outcome measures, secondary outcome measures, and adverse events (that is, the last participant's last visit). The "anticipated" study completion date is the date that the researchers think will be the study completion date.
February 1, 2026

Study Registration Dates

First Submitted

First Submitted

The date on which the study sponsor or investigator first submitted a study record to ClinicalTrials.gov. There is typically a delay of a few days between the first submitted date and the record's availability on ClinicalTrials.gov (the first posted date).
September 16, 2025

First Submitted That Met QC Criteria

First Submitted That Met QC Criteria

The date on which the study sponsor or investigator first submits a study record that is consistent with National Library of Medicine (NLM) quality control (QC) review criteria. The sponsor or investigator may need to revise and submit a study record one or more times before NLM's QC review criteria are met. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
November 17, 2025

First Posted (Actual)

First Posted

The date on which the study record was first available on ClinicalTrials.gov after National Library of Medicine (NLM) quality control (QC) review has concluded. There is typically a delay of a few days between the date the study sponsor or investigator submitted the study record and the first posted date.
November 24, 2025

Study Record Updates

Last Update Posted (Actual)

Last Update Posted

The most recent date on which changes to a study record were made available on ClinicalTrials.gov. There may be a delay between when the changes were submitted to ClinicalTrials.gov by the study's sponsor or investigator (the last update submitted date) and the last update posted date.
November 24, 2025

Last Update Submitted That Met QC Criteria

Last Update Submitted That Met QC Criteria

The most recent date on which the study sponsor or investigator submitted changes to a study record that are consistent with National Library of Medicine (NLM) quality control (QC) review criteria. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
November 17, 2025

Last Verified

Last Verified

The most recent date on which the study sponsor or investigator confirmed the information about a clinical study on ClinicalTrials.gov as accurate and current. If a study with a recruitment status of recruiting; not yet recruiting; or active, not recruiting has not been confirmed within the past 2 years, the study's recruitment status is shown as unknown.
November 1, 2025

More Information

Terms related to this study

Keywords

Other Study ID Numbers

Other Study ID Numbers

Identifiers or ID numbers other than the NCT number that are assigned to a clinical study by the study's sponsor, funders, or others. These numbers may include unique identifiers from other trial registries and National Institutes of Health grant numbers.
  • SyncGait-5725

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

YES

IPD Plan Description

All raw data will be stored in the supervisor's institutional personal Microsoft 365 account for five years, after which it will be permanently deleted. Data will be recorded anonymously using a unique coded numerical ID, known only to the supervisor. The database will be in Excel format. The encoded dataset may be shared with the rest of the research team and the journal where the study will be published, which may, in turn, make the data available to the scientific community for one year following publication.

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

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