## 1 Introduction  
Lateral ankle strain is one of the most common musculoskeletal injuries among individuals who participate in sports and recreational physical activities [1; 2; 3; 4]. After an ankle strain occurs, the damage caused to the ankle joint, the connective tissue, and the surrounding muscles and peripheral nerves mainly reduce the ability of the person's lower extremities to perform movements correctly [5; 6]. Recent systematic reviews showed that the most common factors related to ankle strains include factors such as BMI, ankle plantar and dorsiflexion strength, hip strength, single leg landing performance and previous ankle injuries, along with other psychosocial, predisposing, intrinsic and extrinsic factors [7; 8; 9]. Following initial strains, a high proportion of individuals develop recurrent injuries, associated symptoms, and persistent ankle dysfunction, referred to as chronic ankle instability (CAI) [1; 10]. People with CAI suffer from a combination of ligamentous laxity and reduced sensorimotor control [10; 11], and report mechanical and/or functional instability of the ankle joint [12].  
The literature definitions and research inclusion criteria for people with CAI have demonstrated a wide range of reported characteristics [13], as well as mechanical and functional clinical signs and symptoms [10; 14]. A common complaint by individualswith CAI following an ankle injury is that they experience episodes when the ankle feels unstable or is at risk of giving way when performing functional activities. Determining the incidence of these episodes through a self-reported ankle instability questionnaire is necessary. The Cumberland Ankle Instability Tool (CAIT) questionnaire [15] and the Ankle Instability Instrument questionnaire (AII) [16] are recommended by the International Ankle Consortium for self-report about the frequency and circumstances of these instability episodes [10].  
Being able to appropriately respond to unexpected perturbations is critical for maintaining balance and preventing falls while walking [17]. Response times to unexpected perturbations among healthy individuals are between 70-180 ms post-perturbation [18]. This response attempts to maintain the centre of gravity within the base of support, or through change-in-support responses such as taking a step forward to intersect the line of gravity and increase the base of support [19]. A review of the literature finds that postural reactions following unexpected perturbations correlate strongly to perturbation intensity, direction, and timing with regards to body orientation [19]. Responses may also differ between different standing positions and walking speeds at the time of the perturbation [20; 21]. Such differences may be attributed to different levels of neuromuscular control or overloading, as well as to differences in weight distribution and dissimilar muscle activation patterns occurring in differing conditions of perturbation [22; 23]. In individuals with CAI, changes in the motor control system following damage to the mechanoreceptors could interfere with postural balance, reducing functionality of proprioception-related abilities and the individual's ability to rapidly and accurately respond to the unexpected perturbations [16; 24].  
The aim of this study was to determine whether there is an association between the different mechanical and functional assessments and the ability of individuals to cope with unexpected perturbations when undertaking a range of different standing/walking positions. The study also examined the association between different mechanical and functional ankle instability assessments at the ankle. For this study, we hypothesized a positive correlation between the different mechanical and functional ankle instability assessments; and, that individuals with mechanical and functional ankle instability will have reduced ability to respond to unexpected perturbations in all the different standing/walking positions.