Background: Chronic ankle instability (CAI) develops following an initial ankle sprain injury, and is characterized by recurrent inversion sprains and a sensation of the ankle “giving way”, often accompanied by pain, swelling, and ankle dysfunction. Neuromuscular deficits-particularly alterations in the peroneal muscles, which act as primary ankle evertors are considered key contributors to impaired stability and function in individuals with CAI. Previous studies have reported delayed or earlier onset times of the peroneal muscles and tibialis anterior (TA) in individuals with CAI during tasks such as gait, landing, and perturbation. However, limited research has examined the onset times of the TA, peroneus longus (PL), and peroneus brevis (PB) during the heel raise (HR), which is generally utilized in clinical settings. Objects: This study aimed to compare the onset times of TA, PL, PB, and extensor digitorum longus (EDL) during unilateral HR between individuals with and without CAI. Methods: Thirty participants with and without CAI were recruited. Surface electromyography (EMG) was used to record TA, PL, PB and EDL activity. Muscle onset times were determined relative to the heel-off event, which was identified using a footswitch synchronized with EMG recording. Independent t-test was conducted to compare muscle onset times between groups. Results: Compared with individuals without CAI, those with CAI demonstrated significantly delayed TA, PL, and PB onset times during unilateral HR (p < 0.05). Conversely, no significant between-group difference was observed in the onset time of the EDL (p > 0.05). Conclusion: These findings suggest that delayed onset times of the peroneal muscles and TA may contribute to the sensation of the ankle “giving way” associated with CAI. Strategies targeting earlier activation of the peroneal muscles may help improve ankle stability during HR tasks in individuals with CAI.

INTRODUCTION
MATERIALS AND METHODS
    1. Participants
    2. Instruments and Measurement
    3. Procedure
    4. Data Analysis
    5. Statistical Analysis
RESULTS
DISCUSSION
CONCLUSIONS
FUNDING
ACKNOWLEDGEMENTS
CONFLICTS OF INTEREST
AUTHOR CONTRIBUTIONS
ORCID
REFERENCES

• Ha-yeong Baek(Department of Physical Therapy, The Graduate School, Yonsei University, Department of Physical Therapy, College of Software and Digital Healthcare Convergence, Laboratory of Kinetic Ergocise Based on Movement Analysis, Yonsei University)
• Il-kyu Ahn(Department of Physical Therapy, The Graduate School, Yonsei University, Department of Physical Therapy, College of Software and Digital Healthcare Convergence, Laboratory of Kinetic Ergocise Based on Movement Analysis, Yonsei University)
• Oh-yun Kwon(Department of Physical Therapy, College of Software and Digital Healthcare Convergence, Laboratory of Kinetic Ergocise Based on Movement Analysis, Yonsei University, Department of Physical Therapy, College of Software and Digital Healthcare Convergence, Yonsei University, Wonju, Korea) Corresponding author