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Background and aim: The ability to maintain upright stance is essential in gait and initiation of voluntary movements that are vital not only for sport but also for activity of daily living .Lateral ankle sprains are common in athletes and are most prevalent in jumping sports such as volleyball , football and basketball .Although these injuries are common after direct contact. It may occur in non contact mechanism such as landing from a jump. Neuromuscular control plays a major role in dynamic joint stability. Most of ankle joint injuries occur in jump-landing task and at the end of sport activitiesparticularly when the athlete is fatigued. Our purpose was to evaluate the effects of ankle muscle fatigue on dynamic postural stability in jump landing task. 

Material and methods: Twenty two healthy women athletes (age:22.8±1.7 years, height:160.3±4.9 cm and weight:56.2±5.8  kg) volunteered to participate in this study .Two test sessions were done with a rest period of one week between them . During each session, effect of one group of ankle muscles (sagital or frontal movers) on dynamic postural stability was assessed. Postural stability was evaluated for 5 seconds after landing on force plate by postural stability indices ( Medial/Lateral, Anterior/Posterior, Vertical and Dynamic Postural Stability Indices) before and after isokinetic fatigue of ankle muscles.

Results: The finding indicate significant increase in all stability indices after isokinetic fatigue of ankle muscles (p<0.05).

Conclusion:These results indicate that isokinetic fatigue of ankle muscles significantly decrease postural control ability in healthy women athlete. 

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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)

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Background and Aim: This study was conducted dueto the limited results of past studies in relation to postural control in children with developmental coordination disorders and the importance of postural control with the ability to integrate the vestibular, visual and somatosensory inputs. In this study the postural control of the children with Developmental Coordination Disorder (DCD) and their normal peers was compared under the reduced or the conflicted sensory input conditions.

Materials and Methods: Twenty two children with Developmental Coordination Disorder (16 males, 6 females with mean age of 7 years old and 9 months, SD 1 year and 5 months) and 19 children with normal motor development (13 males, 6 females, with mean age of 6 years and 11 months, SD 1 year and 1 month) were evaluated. Standing balance, sensory organization and motor control strategy were evaluated using the sensory organization test (SOT).

Result: The results showed that the children with DCD had poorer function than the normal children in the composite equilibrium (p&le; 0.001), visual ratios (p=0.005) and vestibular ration (p=0.002). There were no meaningful differences between groups in their average somatosensory ratio. Additionally, children with Developmental Coordination Disorder had lower motor strategy scores than the normal children when they were forced to depend on vestibular cues alone (p < 0.05). The children with Developmental Coordination Disorder had deficits in standing balance control in conditions that included reduced or conflicting sensory signals. The visual and vestibular systems tended to be more involved in contributing to the balance deficits than the somatosensory system. Moreover, children with Developmental Coordination Disorder were tended to use hip strategy excessively when forced to rely primarily on vestibular signals to maintain postural stability.

Conclusion: In order to improve the postural control in the patients, the rehabilitation protocols should focus on the sensory-motor deficits.

Keywords: Postural control, Postural stability, Developmental Coordination Disorder