Background and Aim: Sacroiliac joint (SIJ) is one of the most important elements in normal musculoskeletal function during gait cycle and serve as a shock absorber during heel strike and load transfer from lower limbs to trunk. Its stabilizing is the product of osseous, ligamentus and muscular elements which muscle activity of these muscles (Gluteus Maximus, Biceps Femoris, Multifidus, Erector Spinea, and Latissimus Dorsi) is important in load transfer through SIJ. It seems that the function of the given muscles in sacroiliac joint pain subjects is interrupted. So, the aim of the present study is to compare muscle activity during different events of stance phase of gait cycle during preferred and slow speed between sacroiliac joint pain and healthy subjects.

Methods and Materials: Thirteen SIJ pain subjects (12 females, 1 male) and thirteen healthy subjects (11 females, 2 male) participated in this study. Muscle activity based on RMS from selected muscles was recorded during different events of stance phase of gait either preferred or slow speed by EMG Data-link Biometrics and normalized according to muscle activity during a 500 ms period in rest position before starting walking called Baseline Correction.

Results: Significant statistical differences were found between two groups in muscle activity based RMS during different events of stance (p=0/006), but there was no significant difference in effect of speed on RMS between two groups (p=0/37). Significant Statistical differences were also seen between selected muscles in each group separately during slow speed of walking (p=0/003) but no significant statistical difference during preferred speed in SIJ pain group (p=0/14).

Conclusion: SIJ subjects have showed increased levels of muscle activity during different events of stance phase of gait with preferred and slow speeds. These increased levels can be interpreted as a mechanism to control trunk movements effectively, provide sufficient support and transfer load to lumbar area efficiently.

Key words: Muscle activity, Sacroiliac joint, Gait, Trunk muscle, Lower limb muscles

Background and Aim: Low back pain (LBP) is the most common and expensive musculoskeletal problem in industrialized societies. One in ten people suffers from LBP once in his life. It is self-limited up to 90%, but it is common to repeat. By the way, sacroiliac joint (SIJ) is the origin of low back and pelvic pain in many cases and one of the most important elements in normal musculoskeletal function during gait cycle. Muscles are important to stabilize this joint plus to bones and ligaments. Some of the muscles (Gluteus Maximus, Biceps Femoris, Multi Fidus, Erector Spinae) contributing in gait cycle are important to transfer load through SIJ. The aim of this present study is to compare muscle activity timing during initial and mid stance phase of gait cycle.

Methods and Materials: Sixteen low back pain cases and fifteen healthy subjects participated in this study. A footswitch is placed beneath foot at the suffered side in LBP cases and dominant foot in control group. Two markers were on the 5^th metatarsal bone and lateral maleolus. Electrodes are placed on selected muscles according to SENIAM. Digital camera and EMG Datalink were turned on simultaneously and subject started to walk with his own favorite speed in a specific direction and path. Onset and time to peak of selected muscles were recorded during gait by Datalink and processed by its software.

Results: Low back pain cases showed delayed muscle onset, although it was not significant (P=0.4). Time to peak of all selected muscles in loading response event in LBP group was longer and significant (P=0.01). There was also significant difference in time to peak of all selected muscles during mid-stance event (P= 0.005) except biceps femoris muscle.

Conclusion: Delayed onset and longer time to peak during initial and mid stance phase of gait can be interpreted as a compensatory strategy to control trunk movements effectively, provide sufficient stability and transfer load to lumbar area efficiently.

Key words: Muscle activity, Low back pain, Gait, Trunk muscles, Lower Limb Muscles

Background and Aim: Low back pain (LBP) is the most common and expensive musculoskeletal problem in industrialized societies. One in ten people suffers from LBP once in his life. It is self-limited up to 90%, but it is common to repeat. By the way, sacroiliac joint (SIJ) is the origin of low back and pelvic pain in many cases and one of the most important elements in normal musculoskeletal function during gait cycle. Muscles are important to stabilize this joint plus to bones and ligaments. Some of the muscles (Gluteus Maximus, Biceps Femoris, Multi Fidus, Erector Spinae) contributing in gait cycle are important to transfer load through SIJ. The aim of this present study is to compare muscle activity timing during initial and mid stance phase of gait cycle.

Methods and Materials: Sixteen low back pain cases and fifteen healthy subjects participated in this study. A footswitch is placed beneath foot at the suffered side in LBP cases and dominant foot in control group. Two markers were on the 5^th metatarsal bone and lateral maleolus. Electrodes are placed on selected muscles according to SENIAM. Digital camera and EMG Datalink were turned on simultaneously and subject started to walk with his own favorite speed in a specific direction and path. Onset and time to peak of selected muscles were recorded during gait by Datalink and processed by its software.

Results: Low back pain cases showed delayed muscle onset, although it was not significant (P=0.4). Time to peak of all selected muscles in loading response event in LBP group was longer and significant (P=0.01). There was also significant difference in time to peak of all selected muscles during mid-stance event (P= 0.005) except biceps femoris muscle.

Conclusion: Delayed onset and longer time to peak during initial and mid stance phase of gait can be interpreted as a compensatory strategy to control trunk movements effectively, provide sufficient stability and transfer load to lumbar area efficiently.

Key words: Muscle activity, Low back pain, Gait, Trunk muscles, Lower Limb Muscles