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.    

Background and Aim: Biomechanical conditions of limbs can affect on motor unit recruitment (MUR) markedly. Surface Electromyography (SEMG) is an approach for evaluation of muscle activities and onset time during different functions. The purpose of this study is to use SEMG for detection of central motor control in different functions of knee extensor muscles.

Materials and Methods: Ten healthy subjects contributed in this study. They were done five repetitions of knee flexion/extension in open and close chain separately during recording of SEMG simultaneously. Integrated EMG (iEMG) of three middle repeated cycles were detected according to chain (open- close) and kind of contraction (concentric- eccentric).then the Average of three slope of iEMG compared to each other. 

Results: There were not significant differences in MUR of three extensor muscles for concentric and eccentric contractions in open chain but vastus medialis and lateralis muscles showed significant changes in close chain (P<0.05). Result showed that there were significant differences of MUR for two kind of muscle contractions between open and close chains (P<0.05).  

Conclusion: Recruitment of motor units has not shown difference in open chain between concentric and eccentric contractions. This process indicates representative similarity of control pattern in two kind of contraction in open chain. Concentric contraction at close chain cycle has more MUR in comparison with eccentric contraction. It is equal to more interference of contractible compartment in concentric to eccentric contraction. This happens due to the nature of two kind of contraction particularly in close chain cycle. Comparison between two chains indicated that more motor units contribute in close chain (concentric and eccentric). It means that motor unit recruitment increased due to effect of increase of load in close chain.