This study investigated how chronic ankle instability (CAI) affects functional performance in athletes compared with healthy controls. CAI is a condition that develops after repeated ankle sprains, leading to ongoing "giving way" episodes, pain, and reduced stability.

A total of 32 athletes participated: 16 with CAI and 16 healthy, age- and sport-matched controls. Participants performed a series of sport-specific functional performance tests, including single-leg hop tests, triple crossover hop, lateral hop, 6-meter timed hop, side jump, countermovement jump (CMJ), the 5-10-5 agility test, and the acceleration-deceleration-acceleration (ADA) test. The Deepsport AI program was used for precise measurement of jumping and agility parameters.

Results showed that athletes with CAI had significantly lower jump height and power, reduced hop distances, and slower times in agility and hopping tests compared to controls. These findings suggest that CAI negatively impacts performance in explosive and multidirectional movements, which are essential in sports such as basketball, volleyball, and soccer. No strong correlation was found between CAIT (Cumberland Ankle Instability Tool) scores and objective performance outcomes, suggesting that subjective reports alone may not fully capture functional deficits.

This study highlights the importance of using both subjective questionnaires and objective tests to evaluate ankle instability in athletes. It also supports the need for rehabilitation programs that include not only balance and proprioception training but also specific exercises to improve jumping, agility, and multidirectional performance.

Chronic ankle instability (CAI) is a frequent consequence of lateral ankle sprains, affecting up to 74% of athletes with previous ankle injuries. It is characterized by recurrent sprains, repeated "giving way" episodes, reduced function, and impaired performance. While CAI has been extensively studied in relation to balance and proprioception, its direct effects on sport-specific performance metrics such as jumping and agility remain less clear.

In this cross-sectional case-control study, 32 athletes were enrolled: 16 athletes with CAI and 16 matched healthy athletes with no history of ankle instability. The CAI group was diagnosed using International Ankle Consortium (IAC) criteria (history of ≥1 lateral ankle sprain ≥12 months prior, ≥2 giving way episodes in the past 6 months, CAIT score ≤24, ≥5 years of sports participation). Controls had CAIT scores ≥25 and no ankle injury history.

The testing battery included:

Hop tests: single-leg hop, 6-meter timed hop, triple crossover hop, and lateral hop.

Agility tests: 5-10-5 pro-agility shuttle and acceleration-deceleration-acceleration (ADA) test.

Jump tests: countermovement jump (height, flight time, power) and side jump test.

Measurements were supported by the Deepsport AI program for objective performance analysis.

Inclusion Criteria:

• CAI Group:
• History of at least one significant lateral ankle sprain ≥12 months prior to testing
• At least 2 episodes of ankle "giving way" in the past 6 months
• Cumberland Ankle Instability Tool (CAIT) score ≤24
• Minimum of 5 years of sports participation and ≥3 hours of training per week

Inclusion Criteria - Control Group:

• No history of ankle sprain or ankle instability
• CAIT score ≥25
• Matched to CAI group by age, sex, and sport participation
• Minimum of 5 years of sports participation and ≥3 hours of training per week

Exclusion Criteria:

• History of fracture, surgery, or major injury in the lower extremity within the past year
• Musculoskeletal injury in the knee, hip, or back in the past 3 months
• Neurological or vestibular disorders affecting balance or movement
• Acute ankle pain, swelling, or inflammation at time of testing
• Current use of orthotics or ankle braces during performance testing
• Systemic or cardiovascular disease preventing safe participation

Thirty-two athletes (16 with chronic ankle instability, 16 healthy controls) aged 18-30 years, recruited from volleyball, basketball, and soccer teams. Participants were matched for training background and sport exposure, with both groups averaging ≥5 years of training history and ≥3 hours of weekly participation.

De-identified individual participant data (IPD) from this study, including raw test results (jumping, agility, hop test outcomes), CAIT questionnaire scores, and baseline demographic data (age, sex, sport background), will be shared upon reasonable request for academic research purposes.

De-identified IPD and supporting documents will be available beginning 6 months after publication of the trial results. Data will remain available for 5 years following publication.

Qualified academic researchers may request access to the de-identified dataset, study protocol, and SAP. Requests should be submitted to the corresponding author and will be reviewed by the research team. Access will be granted for scientifically valid proposals and shared via secure data transfer in accordance with institutional and ethical regulations.