Ankle vs. Hip vs. Combined Strengthening in Chronic Ankle Instability

Chronic ankle instability (CAI) is a common condition that can develop after a lateral ankle sprain. Up to 40% of people who sprain their ankle experience a recurrence within a year, and as many as 30% develop persistent symptoms such as ankle "giving way," weakness, or instability. These symptoms can limit daily activities, sports participation, and increase the risk of future sprains. Muscle weakness in both the ankle and hip has been identified as an important factor contributing to CAI. Strengthening these muscles may therefore help improve stability and function. The SHAC study is a randomized controlled trial designed to compare three different strengthening programs in people with chronic ankle instability: (1) an ankle-focused strengthening program, (2) a hip-focused strengthening program, and (3) a combined ankle-hip strengthening program. The goal is to determine which approach leads to the greatest improvement in functional ability, muscle strength, balance, and ankle mobility. A total of 45 participants aged 18 to 35 years with documented chronic ankle instability will be recruited from local sports clubs and the University of Liège. All participants must have a history of at least one ankle sprain that occurred more than 12 months before entering the study, report episodes of ankle instability in the previous six months, and meet specific questionnaire criteria (CAIT \< 24 and FAAM Sport \< 80%). People with recent injuries, previous lower-limb surgery, fractures requiring realignment, neuromuscular conditions, or current pain or swelling will not be able to participate. After the first assessment (T1), participants will be randomly assigned to one of the three groups. Each intervention lasts four weeks and includes three supervised sessions per week. All strengthening exercises are isometric, performed using a handheld dynamometer to measure force accurately. The ankle program includes plantarflexion, dorsiflexion, inversion, and eversion exercises. The hip program includes clamshells, hip external rotation, abduction, and extension. The combined group alternates between hip and ankle exercises. A warm-up and standardized familiarization are performed before each session. All participants will attend two additional assessment sessions: one immediately after the four-week program (T2) and one at a later follow-up time point (T3). During each visit, they will complete functional questionnaires, report their sports participation, and undergo several strength and performance tests. These include hip and ankle muscle strength measurements using a dynamometer, the Heel Rise Test, the modified Y-Balance Test, the Side Hop Test, and a dorsiflexion mobility test. The study aims to identify whether one of the strengthening approaches leads to better functional outcomes for individuals with chronic ankle instability. Understanding these effects may help clinicians design more effective rehabilitation programs for people recovering from ankle sprains and for those experiencing ongoing instability. Participant data will be kept confidential and stored securely in anonymized form for 20 years. Participation is voluntary, and individuals may withdraw at any time without consequences. Results will be presented anonymously in scientific publications and conferences.