Different strategies for landing from different heights among people with chronic ankle instability

Background: Lateral ankle sprain (LAS) usually occurs during landing from heights among people with chronic ankle instability (CAI). Although the kinematics when landing on the flat surface has been reported, no studies have explored the effect of different heights on the landing strategies using a trapdoor device among people with CAI. Research question: Do people with CAI adopt different landing strategies when drop-landing on the trapdoor device from three heights? Methods: Thirty-one participants with CAI (24 males and 7 females, age=21.1±1.8 years, height=176.9±7.4 cm, body mass=71.9±9.2 kg, injured side=18 R&13 L) were recruited. They dropped from three different heights (low height (16 cm), medium height (23 cm), high height (30 cm)) with their affected foot landing on a movable surface of a trapdoor device, which was tilted 24° inward and 15° forward to simulate LAS. Kinematic data was collected using a twelve-camera motion capture system. One-way analysis of variance with repeated measures was used to compare the differences between the three heights. Results: Significant height effects were detected in the peak ankle inversion angle (p=0.009, η²_p=0.280) and angular velocity (p<0.001, η²_p=0.444), and the peak ankle plantarflexion (p=0.002, η²_p=0.360), knee flexion (p<0.001, η²_p=0.555), and hip flexion (p=0.030, η²_p=0.215) angles at the time of peak ankle inversion. Post-hoc tests showed that all the angles and velocities were higher at a low height than at medium (p: 0.001–0.045, d: 0.14–0.44) and high heights (p: 0.001–0.023, d: 0.28–0.66), except for the ankle plantarflexion angle, which was lower at a low height than at medium (p<0.001, d=0.44) and high (p=0.021, d=0.38) heights. Significance: People with CAI adopt a protective strategy during drop-landing at medium and high heights compared to a low height. This strategy involves increased ankle dorsiflexion angle as well as knee and hip flexion angles.