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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: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: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: 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.

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Background and aim: Fatigue is the inability to generate the maximal force that can be produced by the muscle . Fatigue is a subject that patients and athletes frequently encounter. Fatigue is one factor that limits muscle function and may lead to various pain and injury conditions. It is most commonly caused either by repetitive motion or by sustained muscular
contractions. Massage has been used for rehabilitation and relaxation for thousands of years. Massage is widely believed to have a beneficial effect on treating muscle fatigue and has been used in clinical and sports setting for that purpose. There is limited scientific evidence, however, to support the use of massage for enhancing performance and recovery from injury, or for preventing injury. The comparison of massage and rest on the knee extensor muscles fatigue after maximal isokinetic contractions is the main objective of this research.
Materials and methods: Fifteen healthy female aged between 20-30 volunteered to participate in this research. They did at least once a week some non-professional light sporting activities. Each of volunteers was evaluated in 3 different times. The first session was in order to familiarize the volunteers with the test and Isokinetic. For the main test, each of the volunteers was evaluated twice with one week interval. At the start of each session after warm up, the following parameters were measured: Perceived fatigue by Visual Analog Scale ¸average peak torque and average power maximal concentric of quadriceps at the velocity of 60 degrees per second by Isokinetic apparatus. Then in order to fatigue protocol ¸ the subjects were asked to perform successive and maximal quadriceps contractions until three subsequent quadriceps torque output reaches below 50 percent maximal torque output. Afterwards average peak torque and average power was measured. The extent of perceived fatigue was evaluated as before. Subjects then either received massage on the knee extensors or rested for 15 minute duration. Recovery from fatigue was quantified using average peak torque (APT), average power (AP) and perceived recovery scale (VAS).
Results: After maximal fatigue and decrease in torque output, below 50 percent maximal torque, 15 minutes of massage could change APT after fatigue from mean 56.70 (Nm) to 91.53 (Nm)) , AP from 38.64 to 63.62 (Nm) and VAS from 90.06 to 10.20 (mm). After 15 minute rest could change APT from 55.36 to 68.10 (Nm), AP from 37.69 to 48 (Nm) and VAS from 90.06 to 20.73 (mm).
Conclusion: There was significant difference between rest and massage conditions for recovery of fatigue. Massage was an effective intervention for enhancing muscle performance and recovery from fatigue but rest didn`t have such an effect. In both cases, recovery stage (massage or rest) caused significant change in perceived fatigue but massage is more effective on the decrease of perceived fatigue. Therefore, massage has been more effective than rest as a strategy to return to normal state and has caused more relief in perceived fatigue.

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Background and Aim: Muscular fatigue is common problem that an athlete faces repeatedly during sport competition or therapeutic exercise. Undoubtedly¸ fatigue affects the precision of subjects’ performance and limits the range of physical and sport activities. Muscle fatigue advantages and disadvantages have been reviewed in many previous studies. To challenge this controversy fatigue evaluation requires reliable, stable and precise methods of analysis itself. Researches on muscle strength and subject’s perception of fatigue have been done in many studies. Therefore researchers in this study focus on temporal stability of both subjective perception of fatigue and produced muscle torque after fatigue.
Materials and methods: Fifteen healthy female between 20-30 years of age, who at least had some nonprofessional light sporting activities once a week, volunteered in this research. Each of volunteers was evaluated in 3 different sessions. The first session was to familiarize the volunteers with the Isokinetic tests. For the main test, each of the volunteers was evaluated once and then after one week interval. At each session after warm up, perceived fatigue was measured using Visual Analog Scale. Then Average peak torque and average power maximal concentric Isokinetic of quadriceps were measured at the velocity of 60 degrees per second. To perform the fatigue protocol, subjects were asked to perform successive maximal quadriceps contractions until the three subsequent quadriceps torque output drop below 50 percent of maximal torque output. Afterwards, for re-measurement average peak torque, average power and perceived fatigue were evaluated similarly.
Results: The interaclass correlation coefficient (ICC) of average peak torque¸ average power and visual analog scale before performing fatigue protocol were calculated %81.6, %87.4 and %47.9 respectively. The repeated ICC after fatigue has estimated %59.9 ¸%64.4 and %96.6 respectively.
Conclusion: This research demonstrated that Isokinetic temporal stability parameters were high before fatigue. In other words, both torque and power are reliable in two repetition times in a session, as well after one week interval between. After fatigue the stability rate of torque and power recorded by Isokinetic were repeatable and this repeatability has been moderate to high. However VAS showed a completely opposite results, in which before fatigue the stability of imagined local fatigue perception has been very low and was not significant, although after fatigue the VAS showed high repeatability.

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Background and aim: Cognition of fatigue effects on motion response can improve treatment approaches. Determination of mechanism (maximal voluntary contraction and repetition of movement) that cause change of central responses and neuromuscular transmission have specific emphasis in evaluation and treatment of patients. Following fatigue it is arguable which is more important, neural or osteo-ligamental components. Behavior of para spinal muscles due to their roles in control of posture and spinal alignments are more importance. Gesture and motion pattern of neck and lumbar column following fatigue is due to accession of disorder in neuromuscular junction (NMJ) or limitation in reflex response at this system. Reflex influence is not just for muscle fatigue but also it appeared in synergic muscles. It is clear that stimuli and inhibitory ways have important role in this process.
Materials and Methods: Twenty normal subjects (10 female and 10 male) contributed in this study. Tests were including: 1- Training and warm up 2- Placement of recording electrodes on neck extensor muscles at second and forth spinal vertebra of dominant side. 3- Five motion of neck flexion and extension in sitting position at full range without external load. 4- Fatigue test, contain A- Maximal isometric contraction at middle range about 3 minute, which were controlled by a dynamometer until onset of fatigue. B- Fifty dynamic and cyclic motions of neck flexion and extension in full range of it. 5- Perform five motions similar stage 3 immediately after muscle fatigue. Three middle cycles were chosen for evaluation. Degree of off activities in flexion, degree of onset of activities in extension, silent period and mean of muscles activities (RMS), before and after fatigue selected for analysis.
Results: Comparison of two type of fatigue indicated that there are significant differences between them. Range of motion and eccentric activity were similar for two conditions. Isometric fatigue showed more effect than cyclic condition.
Conclusion: In neck motions flexion relaxation occurred. Dynamic motion and isometric activities caused muscle fatigue and changed silent period. This period reduced and it means that onset of extensor muscle activities occurred very soon and moved to middle and outer ranges. In this manner, naught privilege mechanical of non contractile elements in neck region is cause of this reduction. On the other hand extensor muscles have more responsibility for control and preservation of posture. Comparison of two approaches indicated that isometric activity produce more fatigue and spectral indexes such as median and mean frequency reduced markedly.

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Background and Aim: Muscle fatigue is a factor that caused muscle injuries. Ability to perform movement without error and controllability has important role in reduction of injuries. Reproduce ability of motion is reduced after muscle fatigue. Evaluation of motor control can produce suitable conditions for assessment of these changes and help us treatment guide lines for prevention of injuries. The aim of this study was to evaluate motor control changes following onset of fatigue in patients with anterior knee pain as a physiological aspect.
Materials and Methods: Fifteen voluntary female (10 healthy, 5 patients with bilateral syndromes) participated in this study. During dynamic fatigue test (open and closed chain movements), muscle activities were recorded from bilateral vastus medialis, vastus lateralis and rectus femoris (20 healthy and 10 patients quadriceps muscles) by surface electromyography (sEMG). Five dynamic cycles of motions were selected before and immediately after fatigue and then average of three middle cycles were compared for Symmetry Index (SI) as motor control assessment.  Also Median Frequency (MDF) were computed as an indicator for onset of fatigue. 
Results: MDF reduced significantly in both groups. This reduction was markedly showed in patients group. Reduction of SI was significant after fatigue test. Comparison of SI between groups indicated that before fatigue there was significant difference but after fatigue test was not significant.  
Conclusion: Dynamic motions can produce muscle fatigue and reduction of MDF. High central control system used different synergies following pain and functional impairment. Synergy patterns change after dynamic motions fatigue and cause reduction of SI. This change is dependent to pain and functional impairment and has not a stable pattern. 

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Background and Aim: Fatigue is one of the most common problem of multiple sclerosis. It is a sign of inefficiency in the physical, social, and cognitive function. It is a major factor in limiting the responsibilities of social work of patients.The aim of this study was to translate and culturally adapt the Fatigue Impact Scale (FIS) in Iranian and create an appropriate tool for measuring the impact of fatigue and effectiveness of treatment and also rehabilitation interventions on fatigue in Iranian patients. 

Materials and Methods: In order to use the FIS in Iranian patients, the forward  and backward translation and assessing the patient's perspective was done and the Persian version of the questionnaire was prepared.

Results: The questionnaire was completed by twenty patients with multiple sclerosis. The time duration of filling out of each questionnaire took ten to twenty minutes .The final corrections was carried out. All questions of patients was acceptable and understandable and questions of "sexual activity" was completed only by married patients. The question of "financial support" was completed only by employed person (working people). Finally, as much as possible, this questionnaire was adapted with Iranian culture and sentences were confirmed by MAPI Institute.

Conclusion: Persian version of the FIS is an appropriate tool for measuring the impact of fatigue, effectiveness of treatment and rehabilitation interventions on fatigue in patients with multiple sclerosis.

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Background and Aim: With regard to importance of the role of balance in performance of daily activity especially in exercise activity and necessary to identify the factors that influence the balance, the purpose of this study was to survey the effect of lower limb muscle fatigue on balance in elite young athletes.
Materials and Methods: For this purpose, 15 young elite swimmers with a mean age and body mass index 17±0.7 and 21.62±0.5 during the two test phase, were studied. All participants performed the postural Stability and limit of stability tests in six for each test (three repetitions before and three repetitions after fatigue protocol by Wingate test)on the balance Biodex system. Values obtained by the system of the total , anterior - posterior, medial - lateral, anterior, anterior - right, anterior- left, posterior, posterior - right and posterior left index, were analyzed using paired sample t-test(P0.05).
Results: Results showed that fatigue caused a significantly influence the anterior - posterior, medial - lateral, posterior, left and posterior –left index.
Conclusion: With considering the specificity of training principle, the results can be helpful in the design of exercises involving the lower limb muscles in the specific direction. Keyword: Balance, Limit of stability, Fatigue, Athlete.

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Background and Aim: Proprioception is one of the most precise and delicate senses of the human body. It plays an important role in coordination and postural control by protecting the body against trauma and accidents. Although many studies have assessed the effect of fatigue on proprioception in the limbs and the low back region, but a few studies have investigated its possible effect on the cervical region.

  

Material and Methods: Seventeen (8 women, 9 men) young and healthy volunteers were asked to perform the Cervicocephalic Relocation Test (CRT) to the neutral head position by relocating the head on trunk after actively rotating the head to right and left sides, in two conditions before and after muscular fatigue. Absolute, constant and variable errors were used to evaluate cervical joint repositioning accuracy.

  

Results: Fatigue had no effect on cervical joint position sense, Furthermore no considerable difference was seen between male and female subjects (p>0.05).

  

Conclusion: The results suggest that following isometric fatigue of upper trapezuis muscles, no change is produced in the repositioning accuracy of both sexes. Furthermore, sex had no effect on cervical joint proprioception.

  

Key Words: Cervical joint position sense, Fatigue, Proprioception, Cervicocephalic Relocation Test (CRT).

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Background and Aim: Postural control is the ability of maintaining of the body posture in space. Peripheral and central factors have important role in muscle fatigue. Repetitive muscle contraction leads to muscle fatigue. If strength is educed up to 30% of maximum contraction can be disturbed stance control of subjects. The objective of the present study was to compare the effect of lumbar muscle fatigue on postural control in athlete and non-athlete subjects.

  

Materials and Methods: Fifteen men as athlete subjects and other fifteen matched men as non- athlete subjects participated in this study. Trunk extensor muscle fatigue was produced by dynamometer. Stance postural sways were evaluated by force platform device in bipedal stance with open eye.

  

Results: In pre-fatigue state there is no significant difference between two groups. Fatigue had significantly effect on postural sways in both group after Lumbar muscle fatigue specially in non-athlete group (P ≥ 0.05) .

  

Conclusion: The postural control of athletes after muscle fatigue was better than non athlete subjects probably due to better proprioception in athlete subjects.

  

Keywords: Muscle fatigue, Postural control, Force plattform.

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Background and Aim: Fatigue is a factor that disrupts balance and leads to sport injuries. Female athletes have a much higher incidence of ligament injuries than men. The purpose of this study was to assess the effect of gender and functional fatigue on dynamic balance.

Materials and Methods: Thirty two non athletic healthy subjects (16 women and 16 men) aged between 18-35 year participated in this study. Star excursion balance test was performed pre and post functional fatigue at the posterolateral and posteromedial directions.

Results: Main effect of fatigue was significant (F=37.62, P<0.01). Both groups showed reduced reach distance after fatigue in posterolateral and posteromedial directions. Fatigue and group Interaction was not significant (F=0.045, P>0.05). The Interaction of fatigue and directions of star excursion balance test was not significant (F=1.169, P>0.05).

Conclusion: Fatigue reduced the dynamic postural control in both gender. However, this reduction was not different between the groups. It seems that other factors rather than the effect of fatigue on postural control contribute to the difference in the risk of injury between men and women.

Keywords: Functional fatigue, Balance, Gender