This study aims to verify the training effect of smartphone-based training for chronic ankle instability(CAI) subjects. By randomizing subjects to App training group, clinical training group and control group, the training effect will be compared among groups.

Postural control ability may be damaged after ankle sprains. Poor postural control ability is the risk factors of the ankle sprain, forming a vicious circle of recurrent sprains. Proper and early assessment is the key to breaking down the circle. Smartphones have been utilized in the medical field. With built-in sensors, utilizing smartphones as assessment tools can provide quantitative data of postural control performance. This study aims to verify the training effect of smartphone-based training for CAI subjects.

CAI subjects were recruited and randomly assigned to App training group, Home training group and control group, receiving 6 weeks of intervention. Pre-test was conducted before the intervention, and the post-test was conducted after the 6-week intervention. The follow up assessment was conducted 4 weeks after the post-test.

Inclusion Criteria:

• At least one ankle sprain history
• At least 2 times of sprain and feeling unstable
• Diagnosed as functional ankle instability
• Full recovered from injury
• Cumberland Ankle Instability Tool<24
• Ankle Instability Instrument >5 yes
• Identification of Functional Ankle Instability >11

Exclusion Criteria:

• Diagnosis as mechanical instability
• Neurological deficits
• Lower extremity injury within the past 6 wk
• History of lower-extremity surgery
• Other conditions known to affect balance