Effects of Ankle Evertor Fatigue on Force Sense and Neuromuscular Activation in Subjects With Chronic Ankle Instability

Effects of Ankle Evertor Fatigue on Force Sense and Neuromuscular Activation During Submaximal Isometric Contractions in Individuals With and Without Chronic Ankle Instability

The goal of this observational study is to investigate whether ankle evertor muscle fatigue impairs force perception and alters neuromuscular activation patterns during submaximal isometric contractions, and whether these effects differ between individuals with chronic ankle instability (CAI) and individuals without CAI.

Study Overview

• Status: Recruiting
• Conditions: Chronic Ankle Instability, CAI

Detailed Description

Participants will first be familiarized with the research protocol for approximately 20 minutes. After a short break, the experimental protocol with data collection will begin and last between 45 and 60 minutes. Measurements will be performed on the side where the participant reports symptoms of chronic ankle instability. In cases of bilateral CAI, the leg with the lower CAIT score will be tested.

Participants will be tested on an isokinetic dynamometer (Humac Norm, CSMi, USA) in a semi-recumbent position with the hip and knee flexed to ensure comfort and alignment. The trunk and tested leg will be secured with straps to minimize accessory movement. After initial maximal voluntary isometric contraction (MVIC) of ankle evertors, participants will perform force-matching tasks at 25% and 50% of MVIC. Each trial will consist of 5 seconds with visual feedback followed by 5 seconds without feedback, repeated three times per intensity. After completing these tasks, participants will undergo a fatigue protocol for the ankle evertors. After the fatigue protocol, participants will repeat the force-matching tasks at both 25% and 50% MVIC.

The muscle fatigue protocol consists of consecutive isotonic contractions of ankle eversion, performed through the full range of motion at 30% of MVIC torque until visible fatigue. Fatigue will be defined as a clear inability to perform full range of eversion, i.e. the range of motion fell below 10% of the initial value despite evident effort by the participant. The test will be paced using a metronome, with a 1-second concentric and a 1-second eccentric phase to ensure consistent movement velocity.

• Study Type: Observational
• Enrollment (Estimated): 50

Contacts and Locations

• Study Contact: Name: Alan Kacin, PhD, PT, Prof; Phone Number: +38613001119; Email: alan.kacin@zf.uni-lj.si
• Study Contact Backup: Name: Tjaž Brezovar; Phone Number: +38640777919; Email: tjaz.brezovar@zf.uni-lj.si

Study Locations

• Slovenia
  • Ljubljana, Slovenia, 1000
    • Recruiting
    • Faculty of Health Sciences
    • Contact: Martina Oder, PhD, Dean; Phone Number: +38613001112; Email: martina.oder@zf.uni-lj.si
    • Principal Investigator: Alan Kacin, PhD, PT, Prof
    • Sub-Investigator: Tjaž Brezovar

Participation Criteria

Eligibility Criteria

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

• Sampling Method: Non-Probability Sample

Study Population

Participants will be recruited by convenience sampling from the general population and clinical settings.

Description

Inclusion criteria for the healthy control group (no CAI):

• Age between 18 and 45 years,
• No history of injuries or surgical procedures to the lower limbs,
• No peripheral or central neurological impairments.

Inclusion criteria for the chronic ankle instability (CAI) group:

• Age between 18 and 45 years,
• No history of major surgical procedures on the lower limbs
• No peripheral or central neurological impairments,

• Diagnosed chronic ankle instability:

  • First ankle sprain occurred at least one year prior to testing,
  • At least three months since the most recent ankle sprain,
  • Subjective feeling of ankle instability - CAIT (Cumberland Ankle Instability Tool) score < 24.

Exclusion criteria for the CAI group:

- Other pathologies of the ankle joint.

Study Plan

How is the study designed?

Number of groups / cohorts

2

Cohorts and Interventions

Group / Cohort
Healthy group; Healthy participants without a history of ankle sprain or self-reported ankle instability. Participants will complete the same experimental protocol as the group of chronic ankle instability, including a fatigue protocol of the ankle evertors
Chronic ankle instability group; Participants with chronic ankle instability, defined by a history of recurrent ankle sprains and self-reported instability. Participants will complete the same experimental protocol as the control group, including a fatigue protocol of the ankle evertors.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Constant Error (CE)	Muscle force sense will be assessed by the accuracy of force reproduction during force-matching tasks. Constant Error (CE) will be calculated as the mean difference in force (Nm) between reproduction with and without visual feedback during the middle three seconds, averaged across three repetitions at each load level. Unit of measure: Newton-meters (Nm).	Baseline (Day 1, prior to fatigue protocol) and immediately post-fatigue (Day 1, within 5 minutes after fatigue protocol).
Absolute Error (AE)	Muscle force sense will be assessed by the accuracy of force reproduction during force-matching tasks. Absolute Error (AE) will be calculated as the mean absolute difference in force (Nm) between reproduction with and without visual feedback during the middle three seconds, averaged across three repetitions at each load level. Unit of measure: Newton-meters (Nm).	Baseline (Day 1, prior to fatigue protocol) and immediately post-fatigue (Day 1, within 5 minutes after fatigue protocol).
Variable Error (VE)	Muscle force sense will be assessed by the accuracy of force reproduction during force-matching tasks. Variable Error (VE) will be calculated as the standard deviation of errors across three repetitions at each load level. Unit of measure: Newton-meters (Nm).	Time Frame: Baseline (Day 1, prior to fatigue protocol) and immediately post-fatigue (Day 1, within 5 minutes after fatigue protocol).
Coefficient of Variation (CV) of generated force	Ratio of the standard deviation to the mean force during the middle three seconds of sustained contraction in each trial, calculated separately for trials with and without visual feedback. Unit of Measure: Percentage (%).	Baseline (Day 1, prior to fatigue protocol) and immediately post-fatigue (Day 1, within 5 minutes after fatigue protocol).

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Surface EMG root mean square (RMS) amplitude of ankle muscles	RMS amplitude from surface EMG signals of the peroneus longus, tibialis anterior, soleus, and gastrocnemius medialis will be obtained during the fatigue protocol, MVIC and force-matching task. Unit of Measure: millivolts (mV).	Baseline (Day 1, prior to fatigue protocol) and immediately post-fatigue (Day 1, within 5 minutes after fatigue protocol).
Surface EMG median frequency of peroneus longus mucle	Median frequency of EMG signals will be obtained from the peroneus longus during the fatigue protocol, the maximal voluntary isometric contraction (MVIC) and force-matching tasks. Frequency values will be averaged across repetitions. Unit of Measure: Hertz (Hz).	Baseline (Day 1, prior to fatigue protocol) and immediately post-fatigue (Day 1, within 5 minutes after fatigue protocol).
Maximal voluntary isometric contraction (MVIC)	MVIC of the ankle evertors will be measured at the beginning of the protocol to determine the target force for submaximal isometric contractions, and repeated immediately after the fatigue protocol to assess the effectiveness of fatigue, expressed in Newton-meters (Nm).	Baseline (Day 1, prior to fatigue protocol) and immediately post-fatigue (Day 1, within 5 minutes after fatigue protocol).
Ratings of perceived exertion	Description: Ratings of perceived exertion (RPE) will be assessed at the end of each fatigue protocol using the Borg 10 category-ratio scale, with 0 is no effort and 10 is an extreme physical effort.	Baseline (Day 1, prior to fatigue protocol) and immediately post-fatigue (Day 1, within 5 minutes after fatigue protocol).

Collaborators and Investigators

• Sponsor: University of Ljubljana

Study record dates

Study Major Dates

• Study Start (Actual): May 15, 2025
• Primary Completion (Actual): April 14, 2026
• Study Completion (Estimated): May 4, 2026

Study Registration Dates

• First Submitted: September 10, 2025
• First Submitted That Met QC Criteria: November 18, 2025
• First Posted (Actual): November 26, 2025

Study Record Updates

• Last Update Posted (Actual): April 29, 2026
• Last Update Submitted That Met QC Criteria: April 28, 2026
• Last Verified: November 1, 2025

More Information

Terms related to this study

• Keywords: muscle fatigue; proprioception; chronic ankle instability; force sense
• Other Study ID Numbers: 0120-197/2023/3/isokinetic

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES
• IPD Plan Description: All collected IPD in anonymized form.
• IPD Sharing Time Frame: No limit.
• IPD Sharing Access Criteria: All IPD will be shared upon reasoned request for the purpose of further scientific analysis (i.e. systematic reviews, meta-analyzes, etc.). A proposal describing the planned analyzes must be submitted in writing to the principal investigator, Dr. Alan Kacin, by email to alan.kacin@zf.uni-lj.si.
• IPD Sharing Supporting Information Type: STUDY_PROTOCOL; SAP; ICF

Drug and device information, study documents

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