Introduction
Low back pain is one of the most common musculoskeletal disorders, with a reported lifetime prevalence of up to 80% and is also recognized as the leading cause of disability worldwide [1]. Chronic low back pain (CLBP) lasts more than 3 months and has a direct impact on people’s daily activities and causes changes in motor control. The use of electromyography (EMG) has a major role in analyzing the electrical activity of trunk muscles during different postures among patients with CLBP [7]. Although many studies have evaluated biomechanical changes in the trunk and lower limbs in people with CLBP during walking and running, no comparative study has been conducted on the frequency of muscle electrical activity during walking in these people. Therefore, the present study aims to compare the electrical activity of lower limb muscles and core stabilizers in men with CLBP and healthy men during walking.

Methods
This is a quasi-experimental study. The study population consisted of men with chronic back pain aged 20-30 years from Ardabil and Namin counties in Iran. The statistical sample size was determined to be 10 per group using G*Power software, version 3.1.9.7. The samples were purposively divided into healthy (n=10) and CLBP (n=10) groups. An EMG device (EMG Pre-Ampli, Biometrics Ltd, Nine Mile Point Ind. Est, Newport, England) with a sampling rate of 1000 Hz was used to record the electrical activity of the muscles gastrocnemius lateralis, biceps femoris, semitendinosus, gluteus medius, right erector spinae, left erector spinae, left rectus abdominis and right rectus abdominis. The phases examined included the loading response (0-20% of the gait cycle), mid-stance (20-47% of the gait cycle), and the push-off phase (47-70% of the gait cycle). The independent t-test was used for statistical data analysis. Cohen’s d was also used to calculate effect size: d≤0.2 was considered a small effect, >0.8 was considered a large effect and d=0.5-0.8 was considered a medium effect. For all statistical tests, a significance level of 0.05 was considered. Data were analyzed in SPSS software, version 18.

Results 
The CLBP group had the following statistics: Age: 25.4±2.5 years, weight: 79.4±3.6 kg, height: 176.3±7.4 cm. The control group had the following statistics: age: 25.8±2.9 years, weight: 79.0±3.1 kg, height: 176.6±7.1 cm. There was no significant difference between the two groups in demographic characteristics (Table 1).


The results showed a significant difference in the frequency of rectus abdominis electrical activity in the loading response phase of gait in both groups (P=0.019), which was lower in the CLBP group. The results also showed a significant difference in the frequency of semitendinosus muscle activity in the mid-stance phase of gait in both groups (P=0.049), which was higher in the CLBP group. The results also showed a significant difference in the frequency of the left erector spinae activity (P=0.006) and the right rectus abdominis muscle activity (P=0.003) in the push-off phase of gait in both groups, which were lower in the CLBP group. No statistically significant difference was observed in the activity of other muscles in any groups (P>0.05).

Conclusion
There is a significant change in the frequency of electrical activity of the rectus abdominis, semitendinosus, and erector spinae muscles in men with CLBP compared to healthy men.

Ethical Considerations
Compliance with ethical guidelines
The Ethics Committee University of Mohaghegh Ardabili, Ardabil, Iran, approved the study (Code: IR.UMA.REC.1402.064).

Funding
This research did not receive any grant from funding agencies in the public, commercial, or non-profit sectors.

Authors' contributions
All authors contributed equally to the conception and  design of the study, data collection and analysis, interpre-tation of the results, and drafting of the manuscript. Each  author approved the final version of the manuscript for  submission 

Conflicts of interest
The authors declared no conflicts of interest.



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