Biofeedback Training Targeting at Knee Proprioception

Effects of Biofeedback Training on Knee Proprioception in Individuals With a History of Knee Injury: A Pilot Study

The goal of this clinical trial was to learn if a localized knee exercise program with visual and auditory feedback improves joint awareness (proprioception) and movement quality in young adults with a history of knee injuries. It also evaluated the feasibility and safety of performing these exercises. The main questions it aimed to answer were:

1. Does targeted knee training with instant audio and visual warnings improve joint position awareness and decrease movement fear?
2. Is a supervised laboratory biofeedback training program more effective at improving knee function and movement consistency than an independent home training program?
3. How reliable is a manual goniometer compared to an isokinetic machine when measuring joint position errors? Researchers used a crossover design where every participant completed both the home-based training program and the laboratory-based biofeedback program, separated by a two-week rest period, to compare the effectiveness of the two approaches.

Participants did:

1. Complete two separate three-week training blocks (two sessions per week) performing squats, lunge patterns, and sidesteps.
2. Attend testing sessions at the lab before and after each training block to evaluate balance, movement consistency, and joint position awareness.
3. Wear smart shoe insoles and surface body sensors during testing and laboratory training to track force and joint angles.
4. Keep a log of exercises and note any side effects when training independently at home.

Study Overview

• Status: Completed
• Conditions: Knee Injury
• Intervention / Treatment: Behavioral: Localized Knee Proprioception Training Program; Behavioral: Independent Home-Based Proprioception Training

Detailed Description

Fourteen healthy young adults between the ages of 18-35 years were recruited from the student body of the department, friends and families of the students, and by word of mouth. Participants reported to the research laboratory for baseline testing. A randomized crossover design was utilized for this study. Inclusion criteria required that participants had at least one prior injury or trauma to the knee sustained no less than one year prior to enrollment, with any formal physical therapy concluding no less than 6 months prior. Participants were also required to be in generally good health, able to understand English, and capable of following verbal instructions. Exclusion criteria included a current neurological pathology, pregnancy, or any other lower extremity injury or traumatic event within the past year besides the index knee injury.

Upon arriving at the research laboratory, the study procedures were explained to the participants in detail, and they were allocated time to ask questions and decide on participation. Once informed consent was obtained, initial testing proceeded. A unique identification number (e.g., Knee01) was assigned to each participant for data de-identification and tracking. Participants first completed the Tampa Scale of Kinesiophobia (TSK-17) to quantify movement-related fear or fear of re-injury. Anthropometric measurements, including height and weight, were collected using a stadiometer, followed by leg length and lower leg length measurements via a tape measure. The dominant limb was determined by asking the participant to kick a soccer ball, and the history of the injured leg was documented. Participants were instructed to wear the same pair of athletic footwear during all subsequent laboratory and training sessions.

To evaluate knee joint proprioception, joint position sense (JPS) was assessed using an isokinetic dynamometer and a hand-held manual goniometer, with the more involved limb tested first. While seated on the isokinetic dynamometer, the machine passively moved the participant's limb to a target flexion angle (20° or 50°) with eyes open. The participant was instructed to memorize the joint position in space before the machine returned the limb to the starting resting position. Participants were then asked to actively recreate the target angle with eyes closed and hold the position while the dynamometer recorded the final angle. This protocol was repeated for three trials at each target angle (20° and 50°) on both limbs. For the manual goniometry assessment, participants sat on a treatment table with the knee joint line and lateral malleolus marked for consistent alignment. One research assistant positioned the goniometer to the target angle (20° or 50°) while a second assistant passively moved the participant's leg to allow them to perceive the reference position. The leg was returned to the resting position, and the participant actively recreated the target angle with eyes closed. The research assistants recorded the angle using the goniometer across three trials per target angle for both limbs.

Following JPS testing, seven Inertial Measurement Unit (IMU) sensors were secured via straps to the surface of the body (both feet, shanks, thighs, and the sacrum) to capture lower-body kinematics. Smart Insoles were placed inside the participants' shoes to record ground reaction force data. Participants executed a series of functional tasks: a double-leg quiet stance for 30 seconds, a single-leg quiet stance for 1 minute per limb (involved side first), three jump-landing trials, and the Y-Balance Test (involved side first). Participants then completed a dynamic action-perception coupling task starting with the involved limb. Participants were instructed to tap the top of hurdles set at varying heights (6-inch, 12-inch, and 18-inch) positioned either directly in front of or behind them. They performed the tapping task twice per hurdle with eyes looking forward, and then repeated the task with eyes closed. Finally, participants stood in front of the 18-inch hurdle with eyes closed while a research assistant moved them one step sideways. Participants were required to accurately locate and tap the hurdle with eyes closed in the correct direction for 10 consecutive trials. The entire testing session lasted approximately 1.5 hours.

Following baseline testing, participants were randomly assigned to either: 1) an independent home-based training program (Control group), or 2) a laboratory-based biofeedback training program (Feedback group). Both programs were completed twice weekly for 3 weeks.

For the Feedback group, training sessions took place in the research laboratory with seven surface IMUs attached to track real-time knee kinematics. Visual and auditory thresholds were configured at specific target angles (30°, 60°, or 90° of knee flexion) during a standardized exercise circuit. The circuit consisted of a 30-second squat hold (3 trials), 5-meter lateral monster walks to the involved and uninvolved sides, 8 single-leg retro-squats per limb, and 10 double-leg squats. Participants were instructed to move close to the target threshold angle without exceeding it ; exceeding the threshold immediately triggered a visual red bar warning on the monitor and an auditory beep sound. A two-minute rest was provided between joint angle conditions, resulting in a total training session time of approximately 20 minutes.

The Control group performed the identical exercise circuit twice weekly for 3 weeks at home. Rather than numerical biofeedback thresholds, they were instructed to perform the exercises at qualitative "shallow, medium, or deep" knee flexion depths. Research personnel conducted weekly compliance checks using a tracking sheet to monitor home exercise adherence. Missed sessions for either group were permitted to be made up during a designated fourth week.

Post-training testing sessions, matching the baseline protocol exactly, were scheduled within one week of the final training session. Following a strict two-week washout period to eliminate carryover effects, participants crossed over to the alternate training group to repeat the baseline testing, 3-week training intervention, and final post-training assessments.

• Study Type: Interventional
• Enrollment (Actual): 14
• Phase: Not Applicable

Contacts and Locations

Study Locations

• United States
  • West Virginia
    • Huntington, West Virginia, United States, 25702
      • Marshall University

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

• Between the age of 18 to 64 years old.
• If the participants have a prior injury to the knee, the injury must have occurred no less than one year ago with any physical therapy concluding no less than 6 months ago.
• They are able to understand English and follow verbal instructions.

Exclusion Criteria:

• People who have a current neurological or musculoskeletal pathology.
• Pregnant women.
• People who had other injury/traumatic event to the lower extremity in the last year besides the knee.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Crossover Assignment
• Masking: None (Open Label)

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Laboratory Biofeedback Training; Participants completed a 3-week localized knee proprioception training program performed twice weekly in a research laboratory. Surface Inertial Measurement Units (IMUs) tracked real-time knee kinematics during a standardized exercise circuit (squat holds, lateral monster walks, single-leg retro-squats, and double-leg squats). Instantaneous visual (red bar on a monitor) and auditory (beep sound) biofeedback warnings were triggered whenever a participant exceeded pre-set knee flexion thresholds of 30°, 60°, or 90°.	Behavioral: Localized Knee Proprioception Training Program; A 3-week neuromuscular training program performed twice weekly. The protocol consists of a standardized lower-extremity exercise circuit including 30-second squat holds, 5-meter lateral monster walks, single-leg retro-squats, and double-leg squats performed at target knee flexion depths.
Active Comparator: Independent Home-Based Training; Participants completed an identical 3-week localized knee proprioception training program performed twice weekly independently at their home or location of choice. Participants performed the exact same exercise circuit (squat holds, lateral monster walks, single-leg retro-squats, and double-leg squats) as the laboratory group but without any visual or auditory biofeedback equipment. Instead, they were instructed to target qualitative "shallow, medium, or deep" knee flexion depths and maintained a weekly paper compliance log.	Behavioral: Independent Home-Based Proprioception Training; A 3-week neuromuscular training program performed twice weekly independently at the participant's location of choice. Participants execute the identical lower-extremity exercise circuit (squat holds, lateral monster walks, single-leg retro-squats, and double-leg squats) but without any technological biofeedback equipment. Instead, they rely on qualitative instructions to perform the movements at shallow, medium, or deep knee flexion depths. Adherence is monitored via weekly paper compliance logs.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Dispersion Index (DI) from the Action-Perception Coupling (APC) Task	The Dispersion Index measures lower-limb joint coordination and movement consistency across the final 10 tapping repetitions of the APC task. Joint angle time-series data extracted from surface IMU sensors are used to construct a knee-hip angle-angle graph. Polar coordinate angles are calculated throughout the time series and normalized to 100% of the movement cycle. The spread of the polar coordinate angles is determined by calculating the difference between the maximum and minimum values at every 5% interval of the movement cycle. The average value of this spread is defined as the Dispersion Index (DI). A larger DI represents greater movement pattern dispersion (less consistency across repetitions), while a smaller DI indicates higher movement consistency and superior functional coordination.	Change from Baseline (Pre-Training 1) to Post-Training 1 (Week 3), and change from Pre-Training 2 (Week 5, following a 2-week washout) to Post-Training 2 (Week 8)
Absolute Error of Knee Joint Position Sense	The absolute error (measured in degrees) represents the absolute difference between the target knee flexion angle (either 20° or 50°) and the angle actively replicated by the participant with their eyes closed. Lower values indicate better joint position sense and superior proprioceptive accuracy. Measurements were collected using both an isokinetic dynamometer and a manual hand-held goniometer across three trials per angle.	Change from Baseline (Pre-Training 1) to Post-Training 1 (Week 3), and change from Pre-Training 2 (Week 5, following a 2-week washout) to Post-Training 2 (Week 8).

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Tampa Scale of Kinesiophobia (TSK-17) Score	The TSK-17 is a 17-item self-report questionnaire used to quantify a participant's fear of movement or re-injury. Each item is scored on a 4-point Likert scale ranging from 1 (strongly disagree) to 4 (strongly agree). Total scores range from 17 to 68, where a higher score indicates a greater fear of movement and higher kinesiophobia.	Change from Baseline (Pre-Training 1) to Post-Training 1 (Week 3), and change from Pre-Training 2 (Week 5, following a 2-week washout) to Post-Training 2 (Week 8).
Y-Balance Test Composite Score	The Y-Balance Test is a dynamic test used to evaluate a participant's single-leg stance reach and functional stability in three directions: anterior, posteromedial, and posterolateral. The reach distance in each direction is measured and normalized to the participant's leg length to calculate a composite score expressed as a percentage. Higher composite scores indicate superior dynamic balance and functional coordination.	Change from Baseline (Pre-Training 1) to Post-Training 1 (Week 3), and change from Pre-Training 2 (Week 5, following a 2-week washout) to Post-Training 2 (Week 8).

Collaborators and Investigators

• Sponsor: Marshall University

Study record dates

Study Major Dates

• Study Start (Actual): January 30, 2024
• Primary Completion (Actual): October 31, 2025
• Study Completion (Actual): October 31, 2025

Study Registration Dates

• First Submitted: July 2, 2026
• First Submitted That Met QC Criteria: July 2, 2026
• First Posted (Actual): July 9, 2026

Study Record Updates

• Last Update Posted (Actual): July 9, 2026
• Last Update Submitted That Met QC Criteria: July 2, 2026
• Last Verified: July 1, 2026

More Information

Terms related to this study

• Keywords: biofeedback training; knee proprioception
• Additional Relevant MeSH Terms: Wounds and Injuries; Leg Injuries; Knee Injuries
• Other Study ID Numbers: 2128076

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: Individual participant data will not be shared because informed consent was obtained from participants with the explicit assurance that their raw, de-identified data would remain strictly confidential within the immediate research team to protect participant privacy. Furthermore, because this is a small-scale pilot study with a modest sample size, making individual data publicly available increases the risk of inadvertent participant re-identification.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No