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: Active straight leg raise test in patients with sacroiliac joint dysfunction (SIJ ) is accompanied by feeling pain on joint or heaviness and inability to lift the leg. This test has been advocated as reliable and valid test for the quality of load transfer through the lumbo-pelvic region. With respect to the important role of muscles, in pelvic stability and with respect to patients with SIJ dysfunction can not do this test easily. There is no study has been done about assessment and comparison  of changes in muscle timing of pelvic stabilizer muscles and duration of ramping time during ASLR between healthy and patients with SIJ dysfunction 

Materials and methods:Eleven female subjects with clinical diagnosis of sacroiliac joint pain and 15 match healthy female subjects were tested in the supine resting position with the ASLR. Surface electromyography of rectus abdominus , oblique externus , oblique internus  , adductor longus , biceps femoris , gluteus maximus and  erector spine muscles  were recorded during ASLR test. Timing of muscles and ramp time during ASLR  test were acquired and measured in MATLAB software . 

Results: No statistically significance were found in ramp time between two groups. The onset timing of activation of adductor longus (A.L) was delayed on symptomatic side in subject with SIJ pain (P=0.006).

Conclusion: Delayed onset of A.L suggests an alteration in strategy for lumbopelvic stabilization that may disrupt load transfer through the pelvis.