The ankle brace is widely used among patients with FAI and can effectively reduce the incidence of sprain recurrence, especially among athletes.  However, whether ankle braces can reduce the degree of injury is unknown. McGuine et al found that use of lace-up ankle braces reduced the incidence but not the severity of acute ankle injuries in male and female high school basketball athletes both with and without a previous history of an ankle injury.  Current research suggest that an ankle brace can prevent or reduce injuries by affecting proprioception during sudden inversion.  Unfortunately, previous studies are based on induced sudden ankle inversion in a standing or sitting position.     Several studies simulating ankle sprain under more functional situations, such as walking or landing, conclude that the ankle brace or patient’s mental preparation may reduce some of the muscle activation that occurs during ankle inversion.    The lack of data on synchronous kinematic changes after wearing an ankle brace also presents problems when interpreting results. Only one recent study has conducted coupled analysis of the neuromuscular functions and kinematics of the ankle complex;  in this work, the researchers induced rapid sudden ankle inversion on normal subjects and found that an ankle brace could simultaneously restrict inversion and reduce the activity of the PL. The current study cannot fully illustrate the effect of ankle braces on patients with FAI because the subjects were healthy. Thus, our study aimed to reveal the effect of a semirigid ankle brace on the kinematic and neuromuscular functions of patients with FAI through induced ankle inversion during walking.
We studied the kinematics and neuromuscular function of the ankle simultaneously. This current study found some new mechanism of ankle brace during sprain. Ankle brace could effectively reduce the angles and velocities of patients with FAI under rapidly induced ankle inversion movement and synchronously reduce PL activity. We also primarily found a compensatory external rotation mechanism, except when under the direct restriction effect of ankle brace. These findings may provide novel insights into the mechanism of the ankle brace.
When tilt began, the time-related inversion angle of the three groups rapidly increased and then slowly decreased. We found no difference in the peak angles of the three groups. The FAI without brace group had larger maximum inversion angles, larger maximum inversion velocities, and steeper average ankle position–time curves than the two other groups. However, maximum inversion angles and velocities significantly decreased after wearing of the ankle brace. These findings are in accordance with previous studies. Lower inversion angles result in less ATFL and CFL strain, which indicates that the ankle brace can decrease the strain of lateral ligaments at the instance of sprain.  The decrease in ligament strain may contribute to a reduction in the severity of injury when sprain occurs. Besides, significant external rotation synchronous with inversion was observed in the FAI with brace group. A previous biomechanics study showed that compensatory external rotation of the talocrural joint occurs during extreme ankle inversion; this rotation probably occurs against the inversion and adjusts the position of the angle. However, the largest tilt angle observed in the current study was 30°, and results showed no inversion angles over 20°. Considering that compensatory external rotation may not occur under our experimental conditions, we did not find external rotation in the FAI without brace and control groups. Nevertheless, we suppose that the external rotation occurring in the FAI with brace group was activated in advance by the restriction and proprioception regulation of the ankle brace, thus confirming that injury may be reduced after the brace is worm. Moreover, increases in external rotation may decrease the strain of ATFL, which may be another protective mechanism of the brace. 
The sEMG data showed significantly less activation of the PL in the FAI with brace group compared with that in the FAI without brace group. The mechanical support provided by the ankle brace may reduce the demand for muscles when walks or sprain occurs. However, these results contradict previous studies showing increased peroneal stretch-reflex sensitivity   and motoneuron pool excitability  after wearing a brace. Considering that the subjects were tested under sitting or standing conditions in those studies, we feel that our study is more reflective of the actual situation. While our conclusions are similar to those of Barlow , Gehring  and Feger.  Barlow G showed that ankle bracing resulted in lower pre-contact amplitude of the peroneus longus comparing with no brace during walking in patients with chronic ankle instability. Gehring induced rapid sudden ankle inversion on normal subjects and found that an ankle brace could reduce the activity of the PL. In Feger’s research, patients with chronic ankle instability demonstrated decreased muscle activity of ankle, knee, and hip musculature during common functional rehabilitative tasks.In the current study, we consider the combined existence of feedforward and feedback regulations when the sEMG of the PL is reduced. On the one hand, the restriction provided by the ankle brace stimulates cutaneous sensation and sends these impulses to the nerve center; thus, regulation starts before the myotatic reflex of the PL, which corresponds to sEMG reductions before tilt. On the other hand, after tilt begins, the nerve center controls the reflex to an appropriate level according to the subject’s needs, which corresponds to sEMG reduction during tilt, due to the weaker myotatic reflex caused by restriction of the ankle brace. We believe that the relatively low activation of the PL during rapidly induced ankle inversion could relieve muscle fatigue, which contributes to further injury. 
Some methodological limitations should be considered when interpreting our results. First, some risks resulting in injury during rapidly induced ankle inversion exist. Fortunately, no accident occurred during our experiment. Second, the Vicon Motion System is not as accurate as the 3D–2D fluoroscopy image registration technique used in our previous studies,    Thus, the kinematics of the talocrural and subtalar joints were not studied separately. Third, considering the large individual differences in sEMG observed, we only conducted self-control before and after patients in the FAI group wore their ankle brace. Finally, accurate comparisons between different groups require a larger sample size.