Rev Bras Fisiol Exerc 2021;20(1):83-92

doi: 10.33233/rbfex.v20i1.4396

REVIEW

Effects of the back-squat exercise on lower limb myoelectric activity in trained men: a systematic review

Efeitos do exercício de agachamento por trás na atividade mioelétrica de membros inferiores em homens treinados: uma revisão sistemática

 

Rogério Santos de Aguiar1,2, Juliana Brandão Pinto de Castro1,2, Andressa Oliveira Barros dos Santos1,2,3, Giullio César Pereira Salustiano Mallen da Silva1,2,3, Fabiana Rodrigues Scartoni4, Rodolfo de Alkmim Moreira Nunes1,2, Rodrigo Gomes de Souza Vale1,2,5

 

1Universidade do Estado do Rio de Janeiro, Rio de Janeiro, Brasil

2Grupo de Pesquisa em Biodinâmica de Desempenho, Exercícios e Saúde (BIODESA), Universidade Castelo Branco, Rio de Janeiro, RJ, Brasil

3Universidade Católica de Petrópolis, Petrópolis, RJ, Brasil

4Universidade Estácio de Sá, Cabo Frio, RJ, Brasil

 

Received: September 26, 2020; accepted: December 3, 2020.

Correspondence: Rogério Santos de Aguiar, Universidade do Estado do Rio de Janeiro, Instituto de Educação Física e Esportes, Rua São Francisco Xavier, 524, 9 andar, bloco F, sala 9122 20550-900 Rio de Janeiro, RJ

 

Rogério Santos de Aguiar: rogghi@gmail.com

Juliana Brandão Pinto de Castro: julianabrandaoflp@hotmail.com 

Andressa Oliveira Barros dos Santos: professoraoliveiras.and@gmail.com 

Giullio César Pereira Salustiano Mallen da Silva: giulliocesar.gc@hotmail.com

Rodolfo de Alkmim Moreira Nunes: rodolfoalkmim@gmail.com

Fabiana Rodrigues Scartoni: Fabiana.scartoni@ucp.br

Rodrigo Gomes de Souza Vale: rodrigovale@globo.com

 

Abstract

Aim: The aim of this study was to describe the effects of the back-squat exercise on the lower limb myoelectric activity in trained men. Methods: We conducted a systematic review following the recommendations of PRISMA. Medline (PubMed), Scielo, Scopus, SPORTDiscus, and Lilacs databases were searched. The search terms included electromyography, exercise, resistance training, and squat. We included experimental studies that described the back-squat exercise using surface electromyography (EMG) in men experienced in resistance training and back squat exercise at angles from 60º to 90º. Results: Eight studies met the inclusion criteria. The interventions of the included studies ranged from 2 to 7 days. The protocols demonstrated to improve the neuromuscular system and to provide greater acquisition of strength in the muscles involved in performing the back-squat exercise (p < 0.05). Thirty-seven muscles were analyzed, with a predominance of the vastus lateralis, vastus medialis, gluteus maximus, and rectus femoris muscles. Conclusion: The studies investigated in this review showed that the back-squat exercise at angles from 60º to 90º increased the lower limb myoelectric activity recorded in loads of 30% and 100% of 1RM in men experienced in resistance training. However, more studies with higher methodological quality are needed in the analysis of the squat exercise to reduce the risk of bias.

Keywords: electromyography; squat exercise; resistance training; muscle strength.

 

Resumo

Objetivo: O objetivo deste estudo foi descrever os efeitos do exercício agachamento por trás sobre a atividade mioelétrica de membros inferiores em homens treinados. Métodos: Foi realizada uma revisão sistemática seguindo as recomendações do PRISMA. Foram pesquisadas as bases de dados Medline (Pubmed), Scielo, Scopus, SPORTDiscus e Lilacs. Os termos de pesquisa incluíram eletromiografia, exercício, treinamento de resistência e agachamento. Foram incluídos estudos experimentais que descreveram o exercício agachamento por trás por meio da eletromiografia de superfície (EMG) em homens com experiência em treinamento resistido (TR) e exercício agachamento por trás em ângulos de 60º a 90º. Resultados: Oito estudos preencheram os critérios de inclusão. As intervenções dos estudos incluídos variaram de 2 a 7 dias. Os protocolos demonstraram melhorar o sistema neuromuscular e proporcionar maior aquisição de força nos músculos envolvidos na realização do exercício agachamento por trás (p < 0,05). Foram analisados 37 músculos, com predomínio dos músculos vasto lateral, vasto medial, glúteo máximo e reto femoral. Conclusão: Os estudos investigados nesta revisão mostraram que o exercício agachamento por trás em ângulos de 60º a 90º aumentou a atividade mioelétrica de membros inferiores registrada em cargas de 30% e 100% de 1RM em homens experientes em TR. Porém, mais estudos com maior qualidade metodológica são necessários na análise do exercício agachamento para reduzir o risco de viés.

Palavras-chave: eletromiografia; exercício de agachamento; treinamento de resistência; força muscular.

 

Introduction

 

The squat exercise is one of the most used exercises in the prescription of resistance training (RT) and physical fitness. This exercise is also applied to prescriptions intended for clinical treatments. This applicability is due to the capacity of the squat exercise for strengthening the muscles of the lower limbs in the treatment of ligament injuries, patellofemoral dysfunction, and ankle instability [1,2,3].

The squat exercise has also been part of the sports training programs as it presents biomechanical and neuromuscular similarities to a wide range of athletic movements [4]. In this way, it has been included as the central exercise of many sports routines. Once established the biomechanical model, added to an anatomical analysis for its execution, the squat exercise is used to improve physical fitness, with associated benefits that are not limited to the athletic population [5].

Additionally, many activities of daily living (ADL) require the coordinated and simultaneous interaction of various muscle groups. Thus, the squat exercise can be used to improve muscle strength of the lower limbs, favoring the performance of the ADL. This stems from the ability to recruit multiple muscle groups in a single movement [6].

From this perspective, the study of muscles may be important in providing information on the control of voluntary movements, in the analysis of reflexes and measurement of muscle groups involved in the squat exercise [7]. This exercise activates about 200 muscles [6] and can be performed with a variety of depths, usually measured by the degree of the knee flexion, such as partial (knee at 40º angle), half (60, 70 to 90º), and full squat exercise (greater than 90º) [8].

The myoelectric activity of human muscles can be measured by surface electromyography (EMG). The EMG allows measuring the change in membrane potential, that is, how the action potentials are transmitted along with the muscle fiber according to the exercise stimulus performed [9]. Therefore, this systematic review aimed to describe the effects of the back-squat exercise on the myoelectric activity of the lower limbs in trained men.

 

Methods

 

This systematic review followed the recommendations of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [10] and was registered on the International Prospective Register of Systematic Reviews (PROSPERO), as number CRD42018082308.

 

Study eligibility and inclusion criteria

 

We included experimental studies using RT with acute intervention that evaluated the back-squat exercise using EMG in men with experience in RT and squat exercise at 60º to 90º angles. Review studies, studies with individuals who presented some muscle injury or physical limitations, or written in another language other than English, Portuguese, or Spanish were excluded from this study review.

 

Search strategy

 

A search was performed without filters in the Medline (via PubMed), SciELO, Scopus, SPORTDiscus, and Lilacs (via BVS) databases, in May 2020, using the terms “electromyography”, “exercise”, “resistance training” and their respective synonyms, and “squat”. These descriptors and their synonyms were appropriately combined using the logical operators [AND] between descriptors and [OR] between synonyms (Appendix 1). Although the term “squat” was not identified on the Health Sciences Descriptors (DeCS) and Medical Subject Headings (MeSH), it was inserted in the main descriptors as a search strategy because it appeared in some previous studies on the theme. The reference lists and other sources were researched to find further studies.

After the references were extracted using the search terms, they were exported to a shared Mendeley library. Two authors completed the research, the removal of duplicates, the analysis of titles and abstracts, and the screening of complete articles. Any divergences in the analysis were sent to a third author. Then, we read the full version of the articles that met the eligibility criteria of the present study.

 

Bias analysis

 

The ROBINS-I (Risk Of Bias In Non-randomised Studies - of Interventions) tool was used to assess the risk of bias in the studies included in this systematic review [11]. The studies were classified as “selection bias”, “performance bias”, “detection bias”, “monitoring bias”, “report bias”, “lack of data bias”, and “bias” in result selection reported, with the answers “yes”, “probably yes”, “probably not”, and “no”. Two independent and experienced evaluators analyzed the risk of bias in the included studies. Disagreements were assessed by a third researcher.

 

Data collection process

 

The following data were extracted from the selected studies: country, number of participants in each group, age, body mass, height (Table I), intervention protocol, muscles tested, methodologies, tests used for data analysis, and main results (Table II).

 

Results

 

In total, 350 studies were found following the proposed research methodology. After using the selection criteria, eight articles were included in this review (Figure 1).

 

 

Figure 1 - Flow chart of the selected articles

 

Table I presents the descriptive characteristics of the studies included in this review. When analyzing the eight studies [12,13,14,15,16,17,18,19] in Table I, it was observed a population of 107 trained men (mean age: 25.13 ± 1.93 years; body mass: 82.62 ± 2.05 kg; height: 1.74 ± 0.03 m).

 

Table I - Descriptive characteristics of the studies included in the review

 

USA = United States of America; BM = Body mass

 

Table II presents the methodological characteristics and the results regarding the resting conditions in the imposition of the maximum load in all studies, including the muscle strength test used, the muscle group evaluated and the EMG results before and after the intervention. Thirty-seven muscles were analyzed, with a predominance in the analysis of the rectus femoris (RF), vastus lateralis (VL), vastus medialis (VM), gluteus maximus (GM), and rectus femoris muscle.

 

Table II - Methods and outcomes of the studies included in this review (see PDF annexed)

 

Table III shows the studies’ risk of bias through the ROBINS-I tool. Regarding the studies analyzed using the ROBINS-I tool, 70% [13,15,16,17,19] were considered with critical risk of bias, while only 30% [12,14,18] were considered with moderate risk of bias.

 

Table III - Analysis of risk of bias using the ROBINS-I tool

 

P = Probably; 1 = Selection bias; 2 = Performance bias; 3 = Detection bias; 4 = Monitoring bias; 5 = Reporting bias; 6 = Lack of data bias; 7 = Bias in the selection of the reported result

 

Discussion

 

The purpose of this systematic review was to describe the effects of the back-squat exercise on the lower limb myoelectric activity in trained men. The analysis of the eight cross-sectional studies [12,13,14,15,16,17,19] showed greater muscle myoelectric activity during different squat protocols, but these do not represent a greater strength gain promoted by the type of exercise (p < 0.05).

The mean EMG of the RMS signals (20 Hz to 392 Hz) varied for the muscles analyzed (VM, VL, and GM) during the rising phase of the lift with each load during the repetition maximum (RM) tests of the back squat exercise. However, the findings of these experimental studies should be interpreted with caution, as they were classified as uncertain risk of bias (Table III).

As for the interventions, five studies used the RT through free weights with bars and washers [12,13,14,15,19], two [16,17] used barbell and the Smith Machine, and one study [18] did not describe the device used. Furthermore, two of these studies [12,14] performed the RM tests in the back-squat exercise, adding the knee pad. One of these studies [18] performed the 1RM test with loads of 80%, 90%, and 100%, using the EMG in the back-squat exercise. However, general muscle myoelectric activities amplified with increasing loads, but significant increases in EMG signals were observed only in the vastus medialis (VM) and gluteus maximus (GM) muscles with 90% and 100% of 1RM loads. Likewise, Silva et al. [18] when submitted the sample to the squat exercise, observed an increase in the EMG activity of the GM and VM with increasing loads of 60% to 90% of 1RM.

McBride et al. [20] reported the use of heavy loads of 70% to 90% of 1RM to analyze the effect of instability and stability of the back-squat exercise. The results showed a significant increase in the level of the EMG signal in the muscular activity of the vastus lateralis (VL), biceps femoris (BF), and erector of the spine, with the load of 90% of 1RM in the stable back squat exercise. On the other hand, Contreras et al. [21] and Aagaard et al. [22] compared the mean and peak of the EMG amplitude in the back squat exercises in an estimate of 10RM and found no significant differences in the EMG signal in the GM, BF, and VL muscles between the squats. The discrepancy between the findings of these studies may be due to the samples having experience in RT (<3 years). This may suggest a better strategy of muscle recruitment in the frequency of myoelectric activity during the execution of the back-squat exercise used in different percentages of loads and RM [23].

This way, RT with different percentages of repetition maximum (% of 1RM) is used to improve different muscle properties, such as increased maximum strength, explosive strength, and hypertrophy [24]. Additionally, heavy loads (> 80% of 1RM) were used to recruit high threshold fast contraction motor units, according to the size of the muscle fiber, while smaller loads (60% of 1RM) are used to maintain the specificity of the training speed and improve the mechanical power [25]. Loads with different % of 1RM result in different neuromuscular and kinematic adaptations in the eccentric phase of the squat exercise [26].

Hence, the squat exercise is one of the most used exercises in many training protocols due to its applicability and functionality in sports and daily activities. Squat variations (example: back, front, Bulgarian, Sumo, and sink) are applied to physical conditioning, strength training, and physiotherapeutic rehabilitation [27]. Due to biomechanics and neuromuscular similarities to a range of athletic movements, squat is an essential exercise in many sports routines [28].

Thus, the squat aims to train the thigh muscles, the knee extensors (example: rectus femoris, vastus lateralis and vastus medialis), and strengthen the hip extensors (example: gluteus maximus, biceps femoris, and semitendinosus). Moreover, this exercise can develop muscle strength in the lower back, to perform basic skills required in sports and daily activities [29].

It is worth noting that, as the locomotor system adapts to an RT program, the individual must continue to undergo new percentages of load to continue to increase strength and muscle mass by gradually increasing the load and the number of sets or training frequency [30]. These variables are used to maintain the specificity of the speed execution of the squat exercise and improve mechanical power, strength and muscle hypertrophy [31].

All interventions with RT from the experimental studies analyzed in this systematic review are in accordance with the American College of Sports Medicine (ACSM) guidelines [32] for individuals experienced in RT, which includes changes in training loads (<80% of 1RM) to induce acute metabolic, hormonal, neural changes and cardiovascular responses to RT. Also, the 1RM test has been used as a gold standard in determining maximum dynamic strength and uses percentage values of maximum strength to determine training zones [33].

This systematic review has some limitations that should be highlighted. First, the samples were composed only of trained men and did not include women experienced in RT. Therefore, the results cannot be generalized to other populations. However, we opted for the exclusivity of men in the sample, as they tend to have greater body mass and muscle strength than women, due to the higher levels of anabolic hormones. In addition, there is a risk of interference of the muscles close to those analyzed using EMG, which would generate inaccurate edits. Hence, none of the studies was an analysis of the different moments of the myoelectric signal presented in the concentric and eccentric phases of the back-squat exercise with different loads.

 

Conclusion

 

The studies analyzed in the present systematic review showed that the back-squat exercise at angles from 60º to 90º increased the lower limb myoelectric activity recorded in loads of 30% and 100% of 1RM in men experienced in RT. Nonetheless, it is suggested more studies with higher methodological quality in the analysis of the squat exercise to reduce the risk of bias.

 

Potential conflict of interest

No conflicts of interest with potential for this article have been reported.

 

Financing source

There were no external sources of funding for this study.

 

Academic link

This study is linked to the thesis of doctoral student Aguiar RS, from the Postgraduate Program in Exercise and Sports Sciences at the Rio de Janeiro State University.

 

Authors’ contributions

Conception and design of the research: Aguiar RS, Castro JBP, Nunes RAM, Vale RGS, Scartoni FR; Analysis and interpretation of data: Aguiar RS, Castro JBP, Santos AOB, Silva GCPSM; Statistical analysis: Not applicable; Obtaining financing: Not applicable; Writing of the manuscript: Aguiar RS, Castro JBP; Critical review of the manuscript for important intellectual content: Aguiar RS, Castro JBP, Vale RGS.

 

References

 

  1. Deniz E, Yavuz H. Evaluation of muscle activities during different squat variations using electromyography signals. Springer Nature Switzerland 2020;1095:1-7. doi: 10.1007/978-3-030-35249-3_114 [Crossref]
  2. Monajati A, Larumbe-Zabala E, Goss-Sampson M, Naclerio F. Surface electromyography analysis of three squat exercises. J Hum Kinet 2018;67:73-83. doi: 10.2478/hukin-2018-0073 [Crossref]
  3. Rasch PJ, Burke RK. Kinesiology and applied anatomy (5th ed.). Philadelphia/PA: Lea and Febiger; 1974. 604p. doi: 10.1093/ptj/55.6.712 [Crossref]
  4. Escamilla RF, Fleisig GS, Zheng N, Lander JE, Barrentine SW, Andrews JR et al. Effects of technique variations on knee biomechanics during the squat and leg press. Med Sci Sports Exerc 2001;33(9):1552-66. doi: 10.1097/00005768-200109000-00020 [Crossref]
  5. Soleyn N. Analyzing the squat. The Aasgaard Company 2013. p.2-8.
  6. Tillaar RVD, Andersen V, Saeterbakken AH. Comparison of muscle activation and kinematics during free-weight back squats with different loads. PLoS ONE 2019;14(5):1-13. doi: 10.1371/journal.pone.0217044 [Crossref]
  7. Serrão JC, Mezêncio B, Claudino JG, Rafael SR, Miyashiro PL et al. Effect of 3 different applications of Kinesio Taping Denko® on electromyographic activity: inhibition or facilitation of the quadriceps of males during squat exercise. J Sports Sci Med 2016;15(3):403-9.
  8. Yavuz HU, Erdag D. Kinematic and electromyographic activity changes during back squat with submaximal and maximal loading. Appl Bionics Biomech 2017:9084725. doi: 10.1155/2017/9084725 [Crossref]
  9. Safee MKM, Wan AWAB, Ibrahim F, Abu ONA, Abdul MNA. Electromyography activity of the rectus femoris and biceps femoris muscles during prostration and squat exercise. Int J Bioeng Life Sci 2014;8(12):860-3. doi: 10.5281/zenodo.1099010 [Crossref]
  10. Liberati A, Altman DG, Tetzlaff J, Mulrow C, Gøtzsche PC, Ioannidis JPA et al. The PRISMA statement for reporting systematic reviews and meta-analyses of studies that evaluate healthcare interventions: explanation and elaboration. BMJ 2009;339-b2700. doi: 10.1136/bmj.b2700 [Crossref]
  11. Sterne JAC, Hernán MA, Reeves BC, Savović J, Berkman ND et al. ROBINS-I: a tool for assessing risk of bias in non-randomised studies of interventions. BMJ 2016;355-i4919. doi: 10.1136/bmj.i4919 [Crossref]
  12. Clark D, Lambert MI, Hunter AM. Reliability of trunk muscle electromyography in the loaded back squat exercise. Int J Sports Med 2016;37(6):448-56. doi: 10.1055/s-0035-1569366 [Crossref]
  13. Fletcher IM, Bagley A. Changing the stability conditions in a back squat: the effect on maximum load lifted and erector spinae muscle activity. Sports Biomech 2014;13(4):380-90. doi: 10.1080/14763141.2014.982697 [Crossref]
  14. Gomes WA, Brown LE, Soares EG, Silva JJ, et al. Kinematic and sEMG analysis of the back squat at different intensities with and without knee wraps. J Strength Cond Res 2015;9(9):2482-7. doi: 10.1519/JSC.0000000000000922 [Crossref]
  15. Mina MA, Blazevich AJ, Giakas G, Kay AD. Influence of variable resistance loading on subsequent free weight maximal back squat performance. J Strength Cond Res 2014;28(10):2988-95. doi: 10.1519/jsc.0000000000000471 [Crossref]
  16. Mina MA, Blazevich AJ, Giakas G, Seitz LB, Kay AD. Chain-loaded variable resistance warm-up improves free-weight maximal back squat performance. Eur J Sport Sci 2016;16(8):932-9. doi: 10.1080/17461391.2016.1199740 [Crossref]
  17. Silva JJ, Schoenfeld BJ, Marchetti PN, Pecoraro SL et al. Muscle activation differs between partial and full back squat exercise with external load equated. J Strength Cond Res 2017;31(6):1688-93. doi: 10.1519/JSC.0000000000001713 [Crossref]
  18. Silva JB, Lima VP, Castro JBP, Paz GA, Novaes JS, Nunes RAM, Vale RGS. Analysis of myoelectric activity, blood lactate concentration and time under tension in repetitions maximum in the squat exercise. J Phys Educ Sport 2018;18(4):2478-85. doi: 10.7752/jpes.2018.04371 [Crossref]
  19. Yavuz HU, Erdağ D, Amca AM, Aritan S. Kinematic and EMG activities during front and back squat variations in maximum loads. J Sports Sci 2015;33(10):1058-66. doi: 10.1080/02640414.2014.984240 [Crossref]
  20. McBride JM, Larkin TR, Dayne AM, Haines TL, Kirby TJ. Effect of absolute and relative loading on muscle activity during stable and unstable squatting. Int J Sports Physiol Perf 2010;5(2):177-83. doi: 10.1123/ijspp.5.2.177 [Crossref]
  21. Contreras AD, Vigotsky BJ, Schoenfeld C, Beardsley JC. A comparison of gluteus maximus, biceps femoris, and vastus lateralis electromyography amplitude in the parallel, full, and front squat variations in resistance trained females. J Appl Biomech 2016;32(1):16-22. doi: 10.1123/jab.2015-0113 [Crossref]
  22. Aagaard P, Simonsen EB, Andersen JL, Magnusson P, Dyhre-Poulsen P. Increased rate of force development and neural drive of human skeletal muscle following resistance training. J Appl Physiol 2002;93(4):1318–26. doi: 10.1152/japplphysiol.00283.2002 [Crossref]
  23. Campos GE, Luecke TJ, Wendeln H K, Toma K et al. Muscular adaptations in response to three different resistance-training regimens: specificity of repetition maximum training zones. Eur J Appl Physiol 2002;8(1):50-60. doi: 10.1007/s00421-002-0681-6 [Crossref]
  24. Kaneko M, Fuchimoto T, Toji H, Suei K. Training effect of different loads on the force-velocity relationship and mechanical power output in human muscle. Scand J Sports Sci 1983;5(2):50-5.
  25. Cormie P, Deane R, McBride JM. Methodological concerns for determining power output in the jump squat. J Strength Cond Res 2007;21(2):424-30. doi: 10.1519/R-19605.1 [Crossref]
  26. Senter C, Hame S. L. Biomechanical analysis of tibial torque and knee flexion angle: implications for understanding knee injury. Sports Med 2006;36(8):635-41. doi: 10.2165/00007256-200636080-00001 [Crossref]
  27. Gullett JC. Tillman MD, Gutierrez GM, Chow JW. A biomechanical comparison of back and front squats in healthy trained individuals. J Strength Cond Res 2009;23(1):284-92. doi: 10.1519/JSC.0b013e31818546bb [Crossref]
  28. Rice ADA, McNair PJ. Quadriceps arthrogenic muscle inhibition: neural mechanisms and treatment perspectives. Semin Arthritis Rheum 2010;40(3):250-66. doi: 10.1016/j.semarthrit.2009.10.001 [Crossref]
  29. Langford GA, McCurdy KW, Ernest JM, Doscher M, Walters SD. Specificity of machine, barbell, and water-filled log bench press resistance training on measures of strength. J Strength Cond Res 2007;21(4):1061-66. doi: 10.1519/R-21446.1 [Crossref]
  30. Seitz LB, Trajano GS, Dal Maso F, Haff GG, Blazevich AJ. Postactivation potentiation during voluntary contractions after continued knee extensor task-specific practice. Appl Physiol Nutr Metab 2015;40(3):230-7. doi: 10.1139/apnm-2014-0377 [Crossref]
  31. Mangine GT, Hoffman JR, Gonzalez AM, Townsend JR et al. Exercise-induced hormone elevations are related to muscle growth. J Strength Cond Res 2017;31(1):45-53. doi: 10.1519/JSC.0000000000001491 [Crossref]
  32. American College of Sports Medicine position stand. Progression models in resistance training for healthy adults. Med Sci Sports Exerc 2009;41(3):687-8. doi: 10.1249/MSS.0b013e3181915670 [Crossref]
  33. Oliveira LA, Rivera MF, Marzo ESG. Contribuições da velocidade de movimento para o treinamento resistido: uma revisão narrativa. Rev Bras Fisiol Exerc 2020;19(4):322-31. doi: 10.33233/rbfex.v19i4.3892 [Crossref]

 

Appendix 1 - Searches adopted in the present study