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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: Anterior knee pain (AKP or AnKP) is one of the most common disorders of knee. Many studies have been implemented about anterior knee pain and effect of different treatments on this disorder. Todays, this general term has been divided and studied more closely. Knee extension syndrome is one of the common disorders in orthopedic and physical therapy that diagnosed with increased stiffness of quadriceps muscle and causes anterior knee pain. The purpose of this review article is to evaluate this disorder more closely.

Materials and Methods: A literature search was carried out using MEDLINE and SCIENCE DIRECT cite and JOSPT journal database to assess existing literature about anterior knee pain. Furthermore, literatures about the different standpoints of anterior knee pain and effectiveness of different treatments and interventions of anterior knee pain and knee extension syndrome have been identified.

 Results: Fifty articles have been surveyed: forty-two articles evaluated the effect of different treatments on anterior knee pain. Five articles evaluated the various aspects of anterior knee pain more closely and three ones related to knee extension syndrome.

Conclusion: According to these studies results, the causes of anterior knee pain can be classified in two categories: 1) anterior knee pain associated with patellofemoral disorders and 2) anterior knee pain non-associated with patellofemoral disorders. The knee extension syndrome is the cause for anterior knee pain but non-associated with patellofemoral disorders. In this disorder, the tilt angle of patella could be increased and this factor can increase the patients' pain. In contrast to general belief that focuses on tensor fascia lata- ilotiobial band complex (TFL-ITB complex), the rectus femoris muscle stretching should be focused more, because the ilotiobial band has a less effect on patellar tilt. 

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Background and Aim: This study was performed to compare the stiffness of hamstring and rectus femoris muscles in subjects with anterior knee pain and normal subjects.

Materials and Methods: In this non experimental and case-control study, 20 persons with anterior knee pain were selected simply from convenient sample and 20 healthy persons were selected by matching method. proximal and distal stiffness of hamstring and rectus femoris muscles were measured using an isokinetic device in the passive mode. Also, maximal concentric peak torque during flexion and extension movements of hip and knee, in two groups were compared by independent T-test and correlation analysis.

Results: There was no significant difference between anterior knee pain and proximal compartment of rectus femoris(P=0.320) and hamstring(P=0.125) stiffness, but there was significant difference between anterior knee pain and distal compartment of rectus femoris and hamstring stiffness (P<0.001). Significant relationship was found between anterior knee pain and muscles strength (P<0.001). No correlation was found between strength and stiffness of rectus femoris (P=0.356) and hamstring muscles (P=0.643) in patients group, but in healthy subjects this relationship was found (P<0.001). 

Conclusion: In patients with anterior knee pain, hamstring and rectus femoris muscles stiffness increased and muscle strength decreased. Increasing of muscle strength was effective on stiffness in healthy subjects, but there was no relation between them in patients group. Also rectus femoris and hamstring muscles possibly have different proximal and distal neuromuscular compartments.