1. Introduction
Back pain is one of the most common musculoskeletal lesions with a relatively high prevalence in different communities. About 70 to 80 percent of people develop back pain at least once in their lifetime [1]. Back pain is a pathological condition that causes a sense of movement and seems to interfere with a person’s functioning [2]. Most musculoskeletal disorders, such as back pain, result from manual load-bearing activities (especially lifting) [3].
Lifting the load is a complex dynamic task that involves the upper and lower limbs in addition to the spine. Because weightlifting is associated with back pain, many studies have been performed to prevent back pain in the spine [4-6]. Splitocher et al. studied the loading of the spine while lifting objects in a kneeling posture. The results of this study showed the weight and the weight and the final height of the load influence the vertical, anterior-posterior, and lateral shear forces on the spine [7].
There are several ways to lift a load. Previous studies have not identified which method is best for patients with back pain [8]. Therefore, it is necessary to study the activity of abdominal muscles and hamstring in healthy women and women with back pain in three situations by focusing on electromyography.
2. Materials and Method
This study was a quasi-experimental and laboratory study. The statistical sample included 10 women with back pain and 10 healthy women. These subjects had no history of injuries and skeletal abnormalities, which the New York test evaluated. Healthy and sick individuals were selected homogeneously in height, weight, and Body Mass Index (BMI) [9].
The technique of maximum voluntary contraction was used to normalize the data. In this study, subjects performed lifting in two positions of lifting and lowering the load in front of the body (5% of body weight per person) using Squat, stoop, and freestyle techniques [10].
The speed of movement was adjusted using a metronome. Lifting the load, holding the load, the lowering and pause time was performed for 2 seconds. This cycle continued until 5 repetitions of lifting and 5 repetitions of lowering. The rest time between techniques was 1 minute [11-14]. 
A 16-channel ME6000 electromyograph with a sampling frequency of 2000Hz was used to record muscle activity. And 5 muscles were selected for sampling. After the skin was prepared, the electrode operation was performed using disposable adhesive surface electrodes of Ag-Agcl according to the European protocol [15]. Data analysis was performed using SPSS software, and statistical tests of analysis of variance were performed by repeated measures and independent t-test at a significant level (P≤0.05).
3. Results
According to the results of the t-test, the muscle electromyographic activity (MVIC) during lifting in the freestyle technique of biceps and hamstrings was more intense in back pain people than healthy people. The intensity of activity of the hamstrings was higher in people with back pain than in healthy people in squats, and the intensity of internal oblique and hamstring muscles in people with back pain was higher than in healthy people in the stoop. 
In the three postures, the external oblique muscles of people with back pain were more active in the lifting phase than the healthy individuals in squats than the freestyle and stoop. In healthy people, the intensity of biceps and semitendinosus activity was less active in freestyle than in squats and stoops. In contrast, the intensity of semitendinosus activity in patients with freestyle showed a less significant difference than the other two techniques.
In healthy people and people with low back pain in the load lifting stage in three positions: RAB: Rectus Abdominis, EAB: External Abdominis, IAB: Internal Abdominis, BF: Biceps Femoris muscle, ST: Semitendinosus
The intensity of electrical activity of MVIC muscles in healthy people and people with back pain in the load lowering stage was such that the activity of internal abdominal muscle of healthy people in freestyle was less than squat. In people with back pain, the activity of the internal abdominal muscle in stoop was less than in freestyle and squat, and the activity of biceps in healthy people and people with back pain in freestyle was less than in squat and stoop.
4. Conclusion
The results showed the intensity of muscle activity in healthy people and people with back pain during load lifting in freestyle, biceps, and semitendinosus in people with back pain showed more activity than healthy people (Figure 1).



This study obtained favorable results from the intensity of muscle activity in healthy people and people with back pain in the stage of lifting and lowering the load in three positions. In comparing these techniques, the difference in their movement pattern should not be ignored. In the squat technique, the reason for the increase in lumbar flexion in inactive tissues is the participation in creating extensor torque to affect the intensity of muscle activity.
The squat technique puts the most pressure on the lumbar vertebrae, and in sick people, the muscles may work differently to reduce the pain [16, 17]. In the squat technique, the person tries to minimize the flexion of the lumbar vertebrae by bending the knees and lowering the center of gravity, which reduces the loads on the spine more than the other two methods [18].
It is recommended that patients with back pain use the freestyle method that causes the slightest pressure and pain in the lumbar region. In sports rehabilitation of people with back pain, special attention should be paid to the role and strengthening of the hamstring muscles so that the patient has a better performance for lifting activities.
Ethical Considerations
Compliance with ethical guidelines
All ethical principles are considered in this article. The participants were informed about the purpose of the research and its implementation stages. They were also assured about the confidentiality of their information and were free to leave the study whenever they wished, and if desired, the research results would be available to them.

Funding
This research did not receive any grant from funding agencies in the public, commercial, or non-profit sectors. 
Authors' contributions
All authors equally contributed to preparing this article.
Conflicts of interest
The authors declared no conflict of interest.
 

1. Manchikanti L. Epidemiology of low back pain. Pain Physician. 2000; 3(2):167-92. [DOI:10.36076/ppj.2000/3/167]
2. McGill SM, Sharratt MT, Seguin JP. Loads on spinal tissues during simultaneous lifting and ventilatory challenge. Ergonomics. 1995; 38(9):1772-92. [PMID]
3. Blache Y, Begon M, Michaud B, Desmoulins L, Allard P, Dal Maso F. Muscle function in glenohumeral joint stability during lifting task. Plos One. 2017; 12(12):e0189406. [DOI:10.1371/journal.pone.0189406] [PMID] [PMCID]
4. Maduri A, Pearson BL, Wilson SE. Lumbar-pelvic range and coordination during lifting tasks. J Electromyogr Kinesiol. 2008; 18(5):807-14. [DOI:10.1016/j.jelekin.2007.02.012] [PMID] [PMCID]
5. Hu B, Ning X. The changes of trunk motion rhythm and spinal loading during trunk flexion and extension motions caused by lumbar muscle fatigue. Ann Biomed Eng. 2015; 43(9):2112-9. [DOI:10.1007/s10439-015-1248-0] [PMID]
6. Seminowicz DA, Wideman TH, Naso L, Hatami-Khoroushahi Z, Fallatah S, Ware MA, et al. Effective treatment of chronic low back pain in humans reverses abnormal brain anatomy and function.  J Neurosci. 2011; 31(20):7540-50. [DOI:10.1523/JNEUROSCI.5280-10.2011] [PMID] [PMCID]
7. Foster NE, Anema JR, Cherkin D, Chou R, Cohen SP, Gross DP, et al. Prevention and treatment of low back pain: Evidence, challenges, and promising directions. Lancet. 2018; 391(10137):2368-83. [DOI:10.1016/S0140-6736(18)30489-6]
8. Cox JM. Low back pain: Mechanism, diagnosis and treatment. Philadelphia: Wolters Kluwer Health; 2012. https://www.google.com/books/edition/Low_Back_Pain/imVBoQriMf0C?hl=en&gbpv=0
9. Chiou WK, Lee YH, Chen WJ. Use of the surface EMG coactivational pattern for functional evaluation of trunk muscles in subjects with and without low-back pain. Int J Ind Ergon. 1999; 23(1-2):51-60. [DOI:10.1016/S0169-8141(97)00100-5]
10. Bayramoglu M, Akman MN, Klnç S, Çetin N, Yavuz N, Özker R, Isokinetic measurement of trunk muscle strength in women with chronic low-back pain. Am J Phys Med Rehabil. 2001; 80(9):650-5. [DOI:10.1097/00002060-200109000-00004] [PMID]
11. Maiti R, Ray GG. Study on the variation of peak isometric strength and EMG activity in static field-simulated lifting postures. Int J Ind Ergon. 2004; 33(2):109-22. [DOI:10.1016/j.ergon.2003.07.002]
12. Jacobs JV, Henry SM, Jones SL, Hitt JR, Bunn JY. A history of low back pain associates with altered electromyographic activation patterns in response to perturbations of standing balance.  J Neurophysiol. 2011; 106(5):2506-14. [DOI:10.1152/jn.00296.2011] [PMID] [PMCID]
13. Splittstoesser RE, Inflammatory responses to combinations of: Mental load, repetitive lifting and subject personality [PhD dissertation]. Ohio: Ohio State University; 2016. https://etd.ohiolink.edu/apexprod/rws_olink/r/1501/10?clear=10&p10_accession_num=osu1479763594134482
14. Ehsani F, Hajihasani A, Hedayati R. [Relationship between abdominal muscle activity and postural control during standing tasks in females with chronic nonspecific low back pain (Persian)].  J Mazandaran Univ Med Sci. 2017; 27(148):68-78. http://jmums.mazums.ac.ir/article-1-9956-en.html
15. Coenen P, Gouttebarge V, van der Burght AS, van Dieën JH, Frings-Dresen MH, van der Beek AJ, et al. The effect of lifting during work on low back pain: A health impact assessment based on a meta-analysis. Occup Environ Med. 2014; 71(12):871-7. [DOI:10.1136/oemed-2014-102346] [PMID]
16. Newcomer KL, Jacobson TD, Gabriel DA, Larson DR, Brey RH, An KN. Muscle activation patterns in subjects with and without low back pain. Arch Phys Med Rehabil. 2002; 83(6):816-21. [DOI:10.1053/apmr.2002.32826] [PMID]
17. D’hooge R, Hodges P, Tsao H, Hall L, Macdonald D, Danneels L. Altered trunk muscle coordination during rapid trunk flexion in people in remission of recurrent low back pain. J Electromyogr Kinesiol. 2013; 23(1):173-81. [DOI:10.1016/j.jelekin.2012.09.003] [PMID]
18. Konrad P. The abc of emg. A practical introduction to kinesiological electromyography. 2005; 1(2005):30-5.
19. Straker L. Evidence to support using squat, semi-squat and stoop techniques to lift low-lying objects. Int J Ind Ergon. 2003; 31(3):149-60. [DOI:10.1016/S0169-8141(02)00191-9]
20. Faber GS, Kingma I, Bakker AJ, van Dieën JH. Low-back loading in lifting two loads beside the body compared to lifting one load in front of the body. J Biomech. 2009; 42(1):35-41. [DOI:10.1016/j.jbiomech.2008.10.013] [PMID]
21. Marras WS, Davis KG, Jorgensen M. Gender influences on spine loads during complex lifting. Spine J. 2003; 3(2):93-9. [DOI:10.1016/S1529-9430(02)00570-3]
22. Meyers BM, Keir PJ. Trunk muscle response to lifting unbalanced loads with and without knowledge of center of mass. Clin Biomech. 2003; 18(8):712-20. [DOI:10.1016/S0268-0033(03)00121-9]
23. van Dieën, JH, Selen LPJ, Cholewicki J. Trunk muscle activation in low-back pain patients, an analysis of the literature. J Electromyogr Kinesiol. 2003; 13(4):333-51. [DOI:10.1016/S1050-6411(03)00041-5]
24. Hermens HJ, Freriks B, Merletti R, Stegeman D, Blok J, Rau G, et al. European recommendations for surface electromyography. Roessingh Research and Development. 1999; 8(2):13-54.
25. Lotz CA, Agnew MJ, Godwin AA, Stevenson JM. The effect of an on-body personal lift assist device (PLAD) on fatigue during a repetitive lifting task. J Electromyogr Kinesiol. 2009; 19(2):331-40. [DOI:10.1016/j.jelekin.2007.08.006] [PMID]
26. Marras WS, Parakkat J, Chany AM, Yang G, Burr D, Lavender SA. Spine loading as a function of lift frequency, exposure duration, and work experience. Clin Biomech (Bristol, Avon). 2006; 21(4):345-52. [DOI:10.1016/j.clinbiomech.2005.10.004] [PMID]
27. Hart DL, Stobbe TJ, Jaraiedi M. Effect of lumbar posture on lifting. Spine (Phila Pa 1976). 1987; 12(2):138-45. [DOI:10.1097/00007632-198703000-00009] [PMID]
28. Potvin JR, McGill SM, Norman RW. Trunk muscle and lumbar ligament contributions to dynamic lifts with varying degrees of trunk flexion. Spine (Phila Pa 1976). 1991; 16(9):1099-1107. [DOI:10.1097/00007632-199109000-00015] [PMID]
29. Trafimow JH, Schipplein OD, Novak GJ, Andersson GB. The effects of quadriceps fatigue on the technique of lifting. Spine (Phila Pa 1976). 1993; 18(3):364-7. [DOI:10.1097/00007632-199303000-00011] [PMID]
30. Marras, WS, Ferguson SA, Burr D, Davis KG, Gupta P. Spine loading in patients with low back pain during asymmetric lifting exertions. Spine J. 2004; 4(1):64-75. [DOI:10.1016/S1529-9430(03)00424-8]
31. Hagins M, Lamberg EM. Individuals with low back pain breathe differently than healthy individuals during a lifting task. J Orthop Sports Phys Ther. 2011; 41(3):141-8. [DOI:10.2519/jospt.2011.3437] [PMID]
32. Huysamen K, de Looze M, Bosch T, Ortiz J, Toxiri S, O’Sullivan LW. Assessment of an active industrial exoskeleton to aid dynamic lifting and lowering manual handling tasks. Appl Ergon. 2018; 68:125-31. [DOI:10.1016/j.apergo.2017.11.004] [PMID]
33. Khoddam-Khorasani P, Arjmand N, Shirazi-Adl A. Effect of changes in the lumbar posture in lifting on trunk muscle and spinal loads: A combined in vivo, musculoskeletal, and finite element model study. J Biomech. 2020; 104:109728. [DOI:10.1016/j.jbiomech.2020.109728] [PMID]
34. Marras WS, Parakkat J, Chany AM, Yang G, Burr D, Lavender SA, Spine loading as a function of lift frequency, exposure duration, and work experience. Clinical Biomechanics. 2006; 21(4): 345-352. [DOI:10.1016/j.clinbiomech.2005.10.004] [PMID]
35. Wai EK, Roffey DM, Bishop P, Kwon BK, Dagenais S. Causal assessment of occupational lifting and low back pain: Results of a systematic review. Spine J. 2010; 10(6):554-66. [DOI:10.1016/j.spinee.2010.03.033] [PMID]
36. Wrigley AT, Albert WJ, Deluzio KJ, Stevenson JM. Differentiating lifting technique between those who develop low back pain and those who do not. Clin Biomech (Bristol, Avon). 2005; 20(3):254-63. [DOI:10.1016/j.clinbiomech.2004.11.008] [PMID]
37. Stutchfield BM, Coleman S. The relationships between hamstring flexibility, lumbar flexion, and low back pain in rowers. Eur J Sport Sci. 2006; 6(4):255-60. [DOI:10.1080/17461390601012678]
38. Hamberg-van Reenen HH, Ariëns GA, Blatter BM, van Mechelen W, Bongers PM. A systematic review of the relation between physical capacity and future low back and neck/shoulder pain. Pain. 2007; 130(1-2):93-107. [DOI:10.1016/j.pain.2006.11.004] [PMID]
39. Silfies SP, Squillante D, Maurer P, Westcott S, Karduna AR. Trunk muscle recruitment patterns in specific chronic low back pain populations.  Clin Biomech (Bristol, Avon). 2005; 20(5):465-73. [DOI:10.1016/j.clinbiomech.2005.01.007] [PMID]