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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: 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: 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: Swallowing disorder is one of the most important complaints of patients with upper motor neuron lesions.The rate of disphagia increases due to elderly subjects and brain injuries in our society Majority of these patients have hidden aspiration. Electromyographic assessment of swallowing can produce indicators of recovery and treatment effectiveness. This study tries to indicate pattern and recruitment of muscle activity in swallowing by surface electromyography.
Methods and Materials: Twenty healthy subjects (20-50) and ten subjects with swallowing dysfunction contribute at this study. Activities of bilateral orbicularis oris, buccinator, sternocleidomastoid and anterior region of throat muscles recorded during three stage of liquid swallowing include water, juice and honey by surface electrodes. Value of activity (RMS), duration of activity (Dur) , median (Mdf) and band (Banf) frequency of above muscles were measured.
Results: Healthy subjects indicated increase of RMS, Dur, Mdf and Banf of muscles, following increase of sweeten and viscose of liquid (P<0.05). Patients had more increase of this findings at oral muscles markedly, whereas Dur of throat muscle showed more increase in time (P<0.05). Comparison of between two groups indicated patients have more Dur time especially at throat muscles (P<0.05) and in contras reduce of activities and frequency parameters than healthy subjects (P<0.05).
Conclusion: Patients lean to keep liquid in oral phase and during throat swallow have more limitation. Patients may catch early fatigue and dysfunction for maintenance and keep of liquid particularly in throat region and it redound to change of trajectory of liquid to the respiratory tube. Therefore, rehabilitation protocols must enforce on coordination of oropharengeal muscles and recovery by movement therapy patterns.

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Background and Aim: In spite of massive knowledge increase and ergonomic correction, lumbar disorders extremely prevail in working environments. Efforts have been made in order to decrease prevalence of musculoskeletal disorders caused by lifting, carrying and pulling down objects by using some belts. The purpose of this research is to determine the effect of lumbo-pelvic belt in symmetrical load lifting on one of motor control indexes.
Materials and Methods: In this research twenty men were asked to lift objects with different weights of 5.5, 7.5, 9.5 and 12.5 kg in position of complete trunk and hips flexion and knees extension using and not using belt and put them on the target desk. Surface Electromyography has been recorded from two pairs of back muscles and three of abdominal muscles. 
Results: Lifting different loads with belt showed significant increase in symmetrical index (p<0.05). 
Conclusion:  Using belt brings about more coordination in trunk agonist and antagonist muscles activity while lifting the loads.  

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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: Reliability or unreliability of the results achieved from recording of surface electromyography of muscles has always been questioned. The aim of present study was to  measure the reliability of the delayed reaction time of muscle electromyography of the knee joints on the exposure of unexpected rotary turbulence in the transverse plane from the area of supporting surface.

Materials and Methods: Twenty healthy women from 19 to 30 years old and free from any clear deformities in the lower extremities were participated in the present study. Surface electromyography of the six knee musculature was carried out for every subject separately in 4 situations including: External Rotation (Ext Rot) from plantar area on the transverse plane with bent and straight knee, Internal Rotation (Int. Rot) with the same conditions, Single Leg Stance situation in 4 stages, and repeatability of Intra Session through intra-class correlation coefficients when the muscles are in action on the exposure of turbulence in four applied forms were analyzed.

Result: The results from 24 analyzed forms showed that 18 forms of muscles at the time of action had moderate to high repeatability (Monroe Classification)

Conclusion: Regarding reliability, the muscles indicated different amounts in onset latency time, on the exposure of rotary turbulence, according to joint angle and the direction of applying rotation on the transverse plane. In respect to direction of rotation, most of the muscles indicated more reliability on the exposure of external rotation turbulence (clockwise) in relation to internal rotation (anti-clockwise) and also regarding the joint angle in turbulences with straight knee in relation to turbulences with bent knee. 

Keyword: Knee muscles, Surface electromyography, Reliability, Rotational turbulence

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Background and Aim: The structure and function of the hamstring and quadriceps can contribute to the development and process of patellofemoral pain syndrome. As open and closed kinetic chain exercises have different effects on the knee joint, the aim of the current study was to investigate motor control of knee joint in both kinetic chains according to voluntary response index aspect.

 

Materials and Methods: 12 healthy knees and 12 injured knees (6 females in each group) were examined. Surface electromyography were performed in knee muscles including vastus medialis oblique, rectus femoris, vastus lateralis and biceps femoris while the subjects were doing flexion-extension of knee joint by isokinetic dynamometer system and one leg semi-squat movement. Then voluntary response index was calculated.

 

Results: There were no significant difference between the patients and healthy groups (p>0.05). In the patient group, correlation between similarity index and magnitude was seen.

 

Conclusion: Probably in the low intensity patellofemoral syndromes, voluntary response index could not differentiate between healthy and the patient groups. In the patients with patellofemoral syndrome group, correlation between similarity index and magnitude may represent co-contraction in their muscles.

 

Keywords: Patellofemoral pain syndrome, Motor control, Voluntary response index, Surface electromyography