Background and Aim: Forces which applied to ankle joint for control of stability can cause damage to joint if it does not have suitable control. Chronic ankle instability (CAI) is a current disability that can affect on activity daily living of the patients. The aim of this study is to evaluate forces which contribute to control of posture in difficult conditions.

Material and Methods: Postural control was measured by force plate in two groups of CAI and healthy subjects. Eight positions were selected , including of double stances with closed or opened eyes, and single stances with opened eyes (right/ left) with and without a cognitive task. Force changes in two direction medial/lateral and anterior/posterior were evaluated with fractal time series analysis.

Results: Fractal dimension of force in two groups, following dual task in all of conditions reduced significantly (P<0.05). There was not significant different between two groups in double stance with or without dual task. Single stance in patients indicated significant increase of fractal dimension in affected ankle joint (P<0.05) but comparison of two side in healthy subjects did not have difference. Also there was significant increase of fractal in affected ankle joint of patients in comparison with similar side of healthy subjects (P<0.05).

Conclusion: Patients with (CAI) have a problem in regulation of force for control of posture. This difficulty increased and clearly indicated by dual task condition, which can cause susceptible qualifications for recurrent injuries. Fractal dimension is a suitable factor for analysis of control of posture in difficult situations.

Background and Aim: Fractal dimension (FD) as a measure of system complexity and a chaos and nonlinear dynamics tool has appeared successful in distinguishing subjects with different specifications such as proficiency level. The purpose of this research was to evaluate the capability of FD analysis of postural stability in distinguishing elite Wushu sportsman for dispatching to various competitions.

Materials and Methods: Eight elite and eight non-elite Wushu sportsmen from Talou section participated in this research and performed a difficult balance motion called “backward balance”. Center of pressure (COP) traces were recorded and Higuchi algorithm has been used to obtain fractal dimension of COP displacement time series. Average of FD of two groups were compared with an unpaired t-test.

Results: In both directions of anterio-posterior (AP) and medio-lateral (ML), average values of FD in elite group were significantly more than non-elite group (p<0.05). Subsequently, implementing a receiver operating characteristic (ROC) analysis indicated that FD analysis method performance is very good in AP direction (Area under the curve or AUC=0.938) and good enough in ML direction (AUC=0.668).

Conclusions: Postural control system acts more complex in elite group because of their more proficiency. FD analysis of COP time series could help coaches in choosing elite Wushu sportsman even among a group of skilled Wushu sportsmen. 

Keywords: Wushu, Postural stability, Fractal dimension, Receiver operating characteristic (ROC), Center of pressure (COP)