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Bachground and Aim:The anterior cruciate ligament(ACL) has both mechanical and sensory function. Knee joint proprioception has been tested utilizing either reproduction of position or threshold to detection of passive motion in non-weight bearing positions. It has been suggested that more functional and dynamic/active tests of proprioception may clarify the effect of injury and reconstruction on the proprioceptive function of the ACL at the knee.

 The purpose of this study was assessment of knee joint position sense (JPS) following ACL reconstruction in functional position.

Material and Method:12 patients who had undergone ACL reconstruction and 12 healthy control subjects participated in the study.

JPS was evaluated by reproduction of the angles in weight-bearing position with limb movement into flexion and extension.

The dominant-limb knee of healthy subjects and reconstructed and normal knee of the patients were selected for evaluation.

The knee angles were measured  by using a system comprised of digital photography, non-reflective markers and AutoCAD software. Absolute error was considered as a dependent variable.

Results:There were no significant differences between the operated and normal knee of the patients and between the patients and healthy control subjects. These results were observed in two tasks of limb movement into flexion and extension. The position had no significant effect on the absolute error in both groups.

Conclusion and Discussion: The result of this study suggest that subjects who have undergone ACL reconstruction do not have a deficit in knee JPS when tested under functional weight bearing conditions. Knee JPS  is maintained by muscle-tendon receptors providing primary and accurate sensory information for normal proprioceptive function, along with remaining capsular and ligamentous mechanoreceptors which provide additional and/or complimentary proprioceptive information.

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Background and Aim: Several biomechanical and clinical studies have examined the apparent myoelectric silence of the lumbar spine extensor musculature during lumbar flexion from a neutral upright standing posture.

Objective: The purpose of this study was to investigate the relationship between trunk flexibilitiy and flexion relaxation response of the the lumbar erector spinae

Material and Methods: 30 female healthy students were participated in this study which They were arranged in three groups on toe touch test (low flexible,  normal and high flexible).The surface electromyographic from the lumbar erector spinae muscles as well as flexion angle of the trunk, hip and lumbar were recorded. The angle in which electromyographic diminished during flexion and initiated during extension was determined and subjected to one way Anova to determine any significant differences  in the flexion-relaxation response between three groups.

Results: The erector spinae muscles were relaxed in  larger angles during flexion and initiated activity significantly earlier during extension in high flexible group (p<0/001). pearson correlation indicate that there were high correlation between trunk and hip angle during full flexion (r=0/88 p<0/001) and no correlation between trunk and lumbar angle (r=0/1 p< 0.3).

Conclusion: The results indicated that individuals with more flexible trunk , the erector spinae muscles gets relaxed in further angles of the trunk and the hip, furthermore while returing to the upright posture ,this muscle is recruiting sooner than two other groups .the biomechanical basis of this finding relies in ligamentous and passive tissues properties of individuals with different Flexibilities of the trunk which can effect there recruitment pattern of active tissues.

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Background and Aim: In this study, we investigated : 1) The effect of diferent lengths of Abd. policis brevis muscle on variations EMG frequency spectrum. 2) The effect of muscle contractions on frequency spectrum and 3) The effect of different lengths of muscle on local muscle fatigue.

Material and Method: 20 normal subjects participated in this study. (with range of 20 - 34 years old). Each test carried out in four steps. Every person performed 3 minutes of isometric contraction in Abd. policis brevis muscle and EMG signals were saved for 5 seconds before and after the test. Then the  same procedure was performed while individual did 6 minutes free dynamic contraction and 6 minutes high speed dynamic contraction and 6 minutes forceful dynamic contraction respectively.

Results:This study showed that when the individual performed muscle contraction in short length, median and mean frequency increased (P = % 0) and fatigue test caused a decrease in frequency charactristics that was more in dynamic contractions in compare with isometric contraction (it was more obvious in forceful dynamic contraction). These parameters didn't change in different lengths (P = %9, P = %4, P= %3 for 0 - 45, 0 -90 and 45 - 90 degrees respectively).

Conclusion and discussion:This study showed that different muscle lengths and muscle contractions affect on frequency spectrum and it also showed the effect of different muscle lengths and muscle contractions on local muscle fatigue.

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Background and Aim:Measuring the joint angles is used to assess  joint  position sense (JPS). The aim of this study was to introduce a fast, less expensive, objective and simple method of measurement.

In this study, the accuracy and reliability of a system, comprising digital photography, nonreflective markers and AutoCAD analysis (or manual analysis) were evaluated.

Material and Methods: For this purpose, the digital photos were taken from 9 angles of a standard goniometer whereas 4 square markers were been attached on its arms. The goniometer was placed at two locations on a calibration board. The angles were measured by using AutoCAD software via the markers^, corners. Furthermore, the markers were recorded at 72 angles of the knee joint positions in 24 healthy subjects.The knee angles were measured by 3 investigators and by using transparent sheets and goniometry.

Results:ICC was 1 for each location of the goniometer at each reference angle.The variability from the mean angles was approximately less than 0.2 degree. r² was 1 for each location. Intra & inter- rater reliability of the manual analysis were high.

Conclusion:It was noted that the new introduced system, was reliable and precise enough so it could be utilized to measure the joint angles, especially for evaluating the JPS.

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Background and Aim: Mechanoreceptors from the foot sole likely contribute in the reflex regulations. Stimulation of these receptors in the medial aspect of the foot is corresponded to the medial plantar nerve divisions in the tibial nerve. Therefore, it was hypothesized that repetitive low threshold afferents stimulation would have an inhibitory effect on the soleus H-reflexes.

Materials and Methods : sixteen normal subjects voluntarily, participated in the study. Subjects were remained in prone position. The Cutaneous Mechanical Pressure (CMP) (equal to 50% of leg and foot weight) was applied to the ipsilateral medial plantar surface by a designed instrument through a square plate (30 x 30 mm). H reflex as an indicator for excitability of motoneurones was bilaterally elicited before and after the application of the CMP.

Results: The amplitude of H reflex and H/M ratio showed significant differences before and after the Ipsilateral CMP stimulation of the medial side of the foot (p<0.05) furthermore, the latency of  H reflex was also increased (p<0.05). In addition, the effect of CMP stimulation of the IPS stimulation showed more difference than the Contralateral side.

Discussion: The results highlights the modulatory effects of natural stimulation of cutaneous afferents on excitability of Ipsilateral and contralateral motoneurones. This in respect may have practical application in the management of muscle tone disorders in brain and spinal cord injuries.

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Background and Aim: Sports such as baseball, volleyball, and racquet sports demand skills that place substantial load upon the athlete's shoulder when his or her arm is in an overhead or abducted position. Athletes who participate in these sports are consequently at higher risk for overuse injuries of the shoulder. Infraspinatus syndrome is defined as a condition of frequently painless atrophy of the infraspinatus muscle caused by suprascapular nerve neuropathy. The syndrome typically causes symptoms that mimic those of rotator cuff tendinopathy, and the diagnosis is often overlooked until the condition fails to respond to a traditional rotator cuff treatment program.

In this study muscle timing and activities of shoulder rotator cuff compared between normal athletics and volleyball players with infraspinatus syndrome.

Materials and Methods: Thirty voluntary male professional volleyball players (20 healthy and 10 patient) in the range of 20 -30 years contributed in this study. Patients group in base of electroneurography had injury of suprascapular nerve at right side. Subjects lied prone on table and their shoulder were 90 degree of abduction and medial rotation with 90 degree of flexion in elbow with vertically position of forearm at the lateral side of table. Electromyographic activities of maximum voluntary contraction of infraspinatus, middle trapezius and teres minor . Muscles were recorded three times with monitoring of dynamometer for normalization of dynamic activities. Activities (RMS) of above muscles were recorded during three dynamic motions similar to spark skill and onsets of their activities determined by external synchronized apparatus.

Results: There was significant difference between normalized RMS of infraspinatus,. and middle trapezius of patients in dynamic motion (p<0.05). Whereas healthy subjects showed significant difference between infraspinatus. and two other muscles (p<0.05). Comparison of normalized RMS indicated different in all three muscles between two groups (p<0.05).  

The sequence of onset three muscle activities were different between two groups significantly (p<0.05). This sequence in patients was middle trapezius, teres minor and infraspinatus whereas in healthy subjects was middle trapezius, infraspinatus and teres minor. Duration of above muscle activities were different in two groups (P<0.05). In patients infraspinatus were active less than other two muscles.       

Conclusion: Professional volleyball players are candidate of suprascapular nerve and infraspinatus muscle weakness. Synergic and stabilizer muscles after this condition with more activities contribute and caused reduce of accuracy of motion and early muscle fatigue.

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Background and aim:The knee joint is one of the most important joints of human body, witch tolerates many forces while the subject is standing up or walking especially during close chain and squat positions.

Muscle fatigue may causes some modifications on effects of forces and accordingly some changes on strategy of movement, therefore the concentration in thigh muscles impression on continuous movements is a guidance that makes the investigation on these changes so important.

Materials and Methods: Fifteen healthy women in the range of 20-30 years were contributed in this study. Muscle fatigue were applied in separate sessions by maximal voluntary contraction (MVC) in both open and close chains.

Subjects were done five dynamic repetitions of flexion / extension motion of knee before and after fatigue tests. Surface electromyography (sEMG) recorded from vastus medialis (VM), rectus femoris (RF) and vastus lateralis (VL) muscles during all conditions of tests. Normalized electromyography (NEMG) of muscles activities in two conditions of concentric (Con) and eccentric (Ecc), also median frequency (MF) were calculated for fatigue index. Muscle timing or recruitment pattern indicated by onset of muscle activities for both dynamics chains.

Results:  There are significant different of fatigue indexes between before and after fatigue tests (p<0.05).  After fatigue muscle timing delayed in open chain (p<0.05) and recruitment patterns changed from VL- VM- RF to VL-RF-VM. Fatigue test in close chain caused increment of muscle timing (p<0.05), but it did not change recruitment patterns.

Conclusion: After fatigue tests MF reduced little than NEMG. Significant difference occurred in muscle timing. These variations were increase and delay of timing with change of recruitment in open chain. These findings suggest that motor control strategy is will change at different condirions of with and without load situations.

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Background and aim: Ankle plantar flexor is one of the most susceptible muscles to plasticity and contracture after acquired brain injury. The application of thermal agents was introduced before muscle stretch or active exercises in spastic patients for their relaxation effects. The main aim of the present study was to compare the short-term effect of the ultrasound (US) and infrared (IR) on patients with plantar flexor muscle spasticity.

Materials and Methods: 21 patients were randomly allocated placed to either US(n=11)or IR(n=10)groups. The main outcome measures were, H _max / M _max  ratio, Original Ashworth Scale(OAS), active and passive range of motion (ROM).These tests  performed before, immediately after and 15 minutes after the intervention.

Results: There were no significant changes in H _max / M _max ratio and OAS after the intervention in both groups. The significant changes of the H _max / M _max were observed 15 minutes after intervention in the US group .The change in OAS was also statistical significant in IR group in this period. The changes in active and passive ankle dorsiflexion ROM after the intervention were statistically significant in US group. These changes show the significant changes for ankle passive ROM after15 minutes of  the intervention in IR group.

Conclusion: Our findings demonstrate that one session application of the ultrasound and infrared are not effective in the treatment of muscle spasticity. The ultrasound improved the ankle active and passive ROM. Further research is needed.

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Background and aim: Since 1998, the effect of traction on the H- reflex has been investigated by Hiraoka and the other researchers. Some of them have been done on lower extremity and the other on the upper extremity. The effect of traction was assessed by H reflex amplitude. Different results have been achieved. The new method which has been used since 2000, the effect of cervical traction on the H reflex was carried out by measuring H reflex slope .In this experiment the effect of manual cervical traction has been studied on the H slope of the upper extremity. Now we have sought to extend this work by examining the effects of cervical traction with 3 kg force on the H slope of the lower extremity 

Materials and Methods: This study was administered to sixteen healthy men with a mean age 23.12 of years and SD=2.55. The parameters of H reflex were recorded before and after of cervical traction .All data were analyzed with SPSS (V: 11.5).    

Results: The results showed that, there were no significant differences between before and after the application of cervical traction in H reflex parameters, ratio of H max/M max amplitude and M slope. But H slope and ratio of H slope /M slope were increased significantly after the application of traction (P<0.001).

Conclusion: The present study showed that traction with 3 Kg force can increase motor neuron excitability of soleus muscle and this result is against the previous study. This could be due to the application of the new method (H slope), which is more precise.

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Background and aim: Carpal tunnel syndrome is a common disorder, for which various conservative treatments have been suggested. The aim of this randomized clinical trial was to compare the iontophoretic effects of diclofenac and dexamethasone on patients with carpal tunnel syndrome.

Materials and Methods: Twelve hands from seven patients between 30 to 60 years of old (Mean=45.9 SD±8.3) were treated with pre-designed splint and iontophoresis. Four hands were treated with dexamethasone sodium phosphate and eight other hands had iontophoretic administration of sodium diclofenac. Cock-up splints were used for the patients during the course of treatment and 2 weeks follow up. Treatment continued for ten sessions during two weeks. They were advised not to take oral or parenteral anti-inflammatory drugs. Clinical symptom severity (SSS) and functional status (FSS) as well as visual analogue (VAS) scales were evaluated after iontophoretic treatment and two weeks follow up. Electrophysiological parameters such as distal sensory & motor latencies, amplitudes, nerve conduction velocities (NCV) were measured.

Results: Diclofenac group showed significant improvement in SSS score and sensory electrophysiological parameters of median nerve (P<0.05). Although, in dexamethasone group VAS and SSS scores decreased but there were no statistical significant differences in any intervals. With Comparison between two groups showed significant difference in distal motor latency after following up with more improvement in dexamethasone iontophoresis group (P<0.05).

Conclusion: Above findings showed efficacy of splint and iontophoretic administration of sodium diclofenac in treatment of patients with carpal tunnel syndrome. Although dexamethasone group showed no significant change, previous researches suggested the efficacy of ionophoretic administration of this anti-inflammatory medicine in clinical symptoms' improvement. Therefore, the lack of enough participants may be considered as a source for present results in this group. Although comparison between two groups, showed significant difference in distal motor latency after follow up (singnificant results in dexamethasone) but, due to small number of cases in follow up period, the validity of these results is questionable. Further researches are needed to confirm this difference.

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Background and aim:The role of thoraco-lumbar muscles is important in spinal column stability. Following fatigue due to constant activity, these muscles encounter with variable control pattern and variations of median and mean frequencies are little in relation to torque of force. However these parameters are useful in the literatures, but due to complexity of neuromuscular interaction and variety of motor control, signal processing can determine a wide range of changes and measurements.     

Signal processing nonlinear techniques exploit in biologic signals. Variables of nonlinear techniques are recurrence, determinism, entropy and so on.

The purpose of this study was to determine changes of entropy as nonlinear parameter in comparison with linear parameter and applicability of entropic measurements of the erector spinae muscles during fatigue.   

Materials and methods: Ten healthy women and 6 women with nonspecific low back pain (NSLBP) with a range of 20-30 years old patticipated in this study. Surface electromyography of isometric activities recorded from trunk (T12), lumbar (L3) and biceps femoris muscles during modified Sorenson isometric fatigue test. Median and mean frequency and also nonlinear parameters such as entropy and trend measured in one second of muscles activities before and onset of fatigue. 

Results:  Following fatigue in healthy group, median and mean frequencies reduced at a range of 12-20% (p<0.05). This decrement in LBP group was little (4 - 20%, p<0.05). Entropy increased 120-200% and trend reduced 800-2000% in normal subjects (p<0.05), whereas subjects with LBP indicated increment of entropy 65-220% and decrement of trend 240-500% (p<0.05). Before and after fatigue there was a significance difference between two groups in entropy parameter (p<0.05), whereas median and mean frequencies differences were not significant.

Conclusion:Following static positions, fatigue occurred in three levels of above muscles particularly at lumbar region. Traditional fatigue indicators showed good differences, but percentage of variability was low in comparison to nonlinear parameters. It suggests that nonlinear variables especially entropy are more sensitive than traditional indicators and can explain these stochastic behaviors

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Background and aim: Muscle flexibility is an important component of physical fitness and injury prevention.

Passive Stretch can be effective in lengthening and making hamstring more flexible. Popliteal angle measurement is one of the most simple method in studying the efficiency of these methods however, in goniometry measurement, there is not any data about muscle tension and any proper judgment about flexibility.  The goal of this study is to evaluate length and stiffness of the hamstrings by Quick Release Movement before and after the passive stretch.

Materials and methods:14 men (20-30 years old) with shorted hamstring (20 degree or more ext lack in passive knee ext test by popliteal angle measurement) participated in this study. Before and after exercises, popliteal angle  and muscle stiffness  were evaluated with digital goniometer and  Quick Release Movement technique respectively. Evaluation of stiffness was performed in flexion and extension positions.

Results: A significant increase in hamstring length was observed. (P<0.05) There was decrease in stiffness in both position of flex and ext but it was significant when in extension state.(P<0.05)

Conclusion: Findings of this study demonstrate passive stretch's effectiveness in increase muscle length and lessening muscle stiffness. In addition Quick Release Movement can be a suitable method for measuring muscle stiffness.

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Background and aim: The shoulder area is the most complex region of the body and inherently unstable that motions are produced and controlled by sequenced activation of muscles in force couple patterns. It seems that investigating of shoulder muscle activation pattern is essential in the various tasks in healthy subjects due to the unstable structure of the shoulder and vital role of muscles in the stability. In order to evaluate motor control changes in the various movement, designing the therapeutic programs suitable to the shoulder pain and to evaluate effects of physiotherapy and preventing of side effects, this study was conducted. Up to now, it has not been evaluated in the D1flex & D1ext patterns yet.

Materials and methods: Thirteen female healthy volunteers participated in the experiment. Dependent variables of muscle activation such as onset and offset as well as sequencing of muscles (upper trapezius, lower trapezius, serratus anterior, pectoralis major, anterior deltoid and posterior deltoid) of dominant side were calculated during D1flex & D1ext patterns by surface EMG and Data log software in the standing position with speed movement of 25 degree/second.

Results: Special patterns of muscle activation were observed during D1flex & D1ext. Sequencing of muscle activation was different in the both movement patterns. Also, significant differences were found in the latency time of all muscles (p<0.05) except upper fibers of trapezius related to flex/ext goniometer (p=0.33) between both movement patterns.

Conclusion: This study demonstrated that there are special patterns of activation of muscles around the scapulohumeral articulation in the normal subjects. Rehabilitation and conditioning programs should be designed to restore and optimize the activation sequences and task specific functions of these muscles.

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Background and aim: The presence of the flexion relaxation phenomenon (FRP) during trunk flexion represents myoelectric  silence consistent with increased load sharing of the posterior discoligamentous passive structures. A number of studies have shown differences in the FRP between patients with chronic low back pain and healthy individuals, Persistent activation of the lumbar erector spinae musculature among patients with back pain may represent the body's attempt to stabilize injured spinal structures via reflexogenic ligamentomuscular activation for protecting them from further injury and avoiding pain.

Materials and methods: Two groups of female subjects ((20 - 40 years old) were participated in this study. First group consisted of 10 subjects with chronic low back pain (CLBP) and second group consisted of 10 healthy ones as control group. Both groups have performed 5 cycles of trunk flexion - extension . The speed of the movement repetition controlled by an electronic metronome . The EMG signals recorded from T12 and L3 paravertebral muscles and bisepse femoris on the right side. The lumbar flexion motion degree has been measured by the digital flexible goniometry.  All subjects have done Sorenson Back Endurance test in prone laying position. The subjects have extended their trunk up to the horizontal position and sustained in this position up to fatigue level .The subjects leave the table and asked to do 5 more cycle of trunk flexion - extension.

Results:  In patients group there is an increment and significant differences in lumbar flexion degree at the time of muscle EMG off  in comparison with healthy subjects after fatigue test (p<0.05). In both groups, the myoelectric silence period showed a significant change with respect to the pre- fatigue (p<0.05). The median frequencies shifted to lower frequencies after fatigue protocol (p<0.05).

Conclusion: Muscle reflexive responses would change following fatigue protocol. Therefore, the muscle activity will increase after the fatigue period. In the other hand, in patient group the role of the muscles as a stabilizer seems to be increased to enhance the stability at the injured segment after fatigue protocol .This protects the segment against pain and disability.

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Background and aim: Chronic ankle instability (CAI) is a current disability that can affect on activity daily living of the patients. Many studies have indicated postural control deficits in these patients but the effect of a dual task on postural control has not been examined yet.

Materials and methods: Postural stability in CAI patients and healthy subjects was measured using the Force Plate. Eight positions concluded two different stances (double & single) with closed or opened eyes. All positions concurrently were done with a cognitive task. Anterior/posterior (Rfa) and medial/lateral (Rsw) mean sway quantified static postural stability.

Results: Mean sway significantly increased in patients in the anterior/posterior (single and double leg stance) and medial/lateral (single leg stance) directions (P<0.05). While performing a dual task anterior/posterior mean sway decreases within the patients group on the impaired leg stance (P<0.05). No difference is seen in the healthy subjects.

Conclusion: Postural control deficits were identified in participants with chronic ankle instability. In view of the fact that a cognitive task resulted in decreasing displacement of center of pressure in patients, this method may identify as an examination and a plan of treatment for affecting on ankle stabilizing factors.

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Background and aim: Muscles that contribute in production of sound have an important role in specific language. Knowledge of normal activities of these muscles is very important in language dysfunction and pathologic conditions. Needle electromyography is complementary approach in clinical evaluations of above conditions but it is a painful method for evaluating of the patient. Surface electromyography can be used to neurophysiological behaviors and effect of treatment interventions and is accepted by scientific academies. The purpose of this study is appointment of new approach in this area.

 Materials and methods: Sixty eight healthy subjects (34 female and 34 male) in range of 20-30 years old were contributed after supplement of questioner form in this study. Subjects sat in a chair with arm rest and recording electrodes placed on muscles of Thyroarytenoid and Cricothyroid of both side (right and left) at middle and lower parts of throat, near of 1 cm from midline.  Silent activity and fricative voice (z-zh) and voiceless (s-sh) activities recorded randomly at 10 second with interval rest between them for 5 repetition. All of signals processed and then compared in time, frequency and non linear measurements.

 Results: Non linear values such as Percent of recurrence, Entropy were reduced significantly in fricative voice (P<0.05).

 Conclusion:  Surface activity recording of Thyroarytenoid and Cricothyroid muscles is possible and sensitive parameter is non linear values. Surface electromyography is new approach for assessment of above muscle in clinical evaluation of speech pathologic conditions.    

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Background and aim: Asymmetric motions of trunk, external forces and other occupational factors such as frequent bending and twisting, lifting and forceful movement contribute to low back disorders. However, the dynamic and three-Dimensional motions of trunk at varying exertion levels were not addressed in literature. Hence, the aim of this study was to investigate the movement pattern and motor output during resisted trunk three-dimensional motion. 

Materials and Methods: Thirty healthy male subjects randomly performed dynamic asymmetric trunk motion at four resistance levels (nominal resistance, 25%, 50%, and 75% maximal voluntary contraction (MVC) torque) while positioned in standing with the L5-S1 interspinous space aligned with the flexion / extension axis of isostation B200. Under each resistance condition, movement patterns (range of motion), motor output (maximum torque) of the trunk were measured.

Results: In general, with increasing resistance from nominal to 75% MVC torque, the maximum torque of trunk in different directions of motion (flexion, extension, right & left lateral flexion, right & left rotation) increased significantly (p= 0.000). With increasing resistance from nominal to 50%  MVC torque, the range of motion of the trunk decreased significant (p<0.0083), but no significant change was found in this variable between resistance conditions of 50% and 75% MVC torque (p>0.0083).

Conclusion: When the resistance level is increased , the created external forces  must be balanced by internal forces generated by trunk muscles. Because the muscles have short lever arms compared with the external forces, they must generate large amounts of forces, placing compressive and shear loads on the structures of the spine. Under these conditions, spine injuries may be enhanced.

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Background and aim: Belts and back supports are frequently used to prevent low back pain. Despite many studies, there are not sufficient evidence and conclusive consensus about the effects of these supports. The purpose of the present study was to determine the effect of lumbosacral supports on motor control pattern during combined trunk motion.

Materials and Methods: 30 healthy young men were selected for the study. Temporal parameters of motor control and activity level of three pairs of trunk muscles were measured during combined trunk motion against minimum resistance and resistance equal to 50% of maximal isometric strength, under with and without back support conditions.

Results: By application of a lumbosacral support, movement response time was significantly decreased under minimum resistance (P=0/004). Application of support decreased reaction time and motor time under two resistance conditions significantly (P<0/05). No significant changes were found in trunk muscle activity levels following wearing a back support (P>0/05).

 Conclusion: By application of a lumbosacral support, individual reaction time was decreased. Although back support did not change the trunk muscle activity level, but the erector spinae muscle efficiency was increased to initiate desired movement.

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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: Neck muscles contract dynamically in the majority of daily activities. Athletes, agricultures and industrial labors are predisposed to muscular fatigue. Aim: The aim of the present study was to compare the effect of dynamic fatigue on power and frequency domains of EMG spectrum.
Material and methods: In this study 20 healthy young men contracted neck muscles dynamically, until muscular fatigue occurs. Surface electromyography was recorded of levator scapula, neck paraspinals and upper trapezius, as neck extensors. The effects of dynamic contraction on frequency (Median Frequency) and Power domains(RMS) were compared before and after fatigue.
Results: The results of the present study indicated that MedF decreases following dynamic fatigue (P<0.05). After dynamic fatigue, RMS of levator scapula and upper trapezius increased significantly (P<0.05). Regarding to significant decrease of RMS and increase of MedF, paraspinals encountered with force reduction .
Conclusion: Changes of MedF and RMS indicated that a continuous dynamic contraction tends to exhaust levator scapula and upper trapezius but decreases paraspinals force.