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.

Background and aim: In physical evaluations, measuring the joint angle is one of the most important outcomes to assess the patient's progress, the effectiveness of various treatment techniques and to delineate the need for future treatments. The aim of this study is to study the reliability of a system consists of skin markers, digital photography, and AutoCAD software for measuring the knee joint angles.

 Materials and methods: In first section, reliability of markers placement was evaluated within three different intervals (five minutes, two days, and twenty days). At second section, reliability of digital photography was evaluated while position of the skin markers and subjects was the same. At the end, in third section, reliability of angle measurement by means of AutoCAD software was assessed.

Results: In first section, the ICC for test-retest reliability of markers placement between first and second sessions, first and third sessions, and also first and forth sessions were 0.97, 0.94, and 0.73, respectively. In second section, the ICC for test-retest reliability of digital photography was 0.99 and in third section, the ICC for intra-rater reliability of angle measurement by means of AutoCAD software was 0.99 (p=0.05).

Conclusion: It was noted that the introduced system was highly reliable, so it could be utilized to measure the knee joint angles.

Background and Aim: The rapid growth of the athletic training profession has been accompanied by an equally rapid increase in focus on basic and clinical research. Lateral ankle sprain (LAS) is an extremely common athletic injury. Despite extensive clinical and basic science research, the recurrence rate remains high. Chronic ankle instability (CAI) following LAS is hypothesized to predispose individuals to re-injury because of neuromuscular control deficits which result following injury. No investigation has been carried out on the existence of joint position deficits in the knee joint of patients with CAI. In this study, joint position sense (JPS) was evaluated in patients with CAI.

Materials and Methods: Ten female patients with CAI and ten healthy control subjects participated in this study. JPS was evaluated by reproduction of the angles in two standing and sitting positions, and in each position two target angles were tested. The knee joints in both lower limbs of patients and the dominant knee-limb of healthy subjects were evaluated. The knee angles were measured by using a system comprised of skin markers, digital photography, and Auto CAD software. Absolute error was considered as a dependant variable.

Result: There were no significant differences between the knee JPS of dominant leg in healthy subjects and both knee joints of patients. There were also no significant differences between knee JPS in two standing and sitting positions and in two different target angles (p>0/05).

Conclusion: The result of this study suggests that subjects who have CAI do not have deficit in knee JPS when tested in sitting position and also under functional weight bearing 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. 

Background and aim: Human knee joints experience very large loads and motions during regular daily, occupational and sport activities. Consequently, they are at high risk of being exposed to injuries and degeneration. Osteoarthritis and ligament injuries often inflict knee joints causing considerable pain and loss of productivity involving thus significant human and economic costs. Hence, biomechanics of human knee joints has been the focus of many investigations with the primary aim to improve understanding of joint function in normal and perturbed conditions. The existing prevention and treatment programs have been based on such studies.
Material and Methods: Due to inherent costs, limitations, difficulties and ethical concerns associated with in vivo and in vitro cadaveric studies, finite element model studies have been developed as effective, powerful and complementary tools to investigate knee joint biomechanics subject to internal and external mechanical conditions affecting its normal function.
Results: The advantage of finite element method in study of joint biomechanics lies in its robustness to incorporate complex 3D joint geometry, intricate boundary and loading conditions and materials with nonhomogeneous and nonlinear properties.
Conclusion:This article reviews important model studies, presents their relevant results and discusses some of the promising future directions.