Immediate effects of using insoles with various wedges on activation and co-contraction indices of selected trunk muscles during load lifting
Introduction
Trunk muscles play an important role during all daily activities (e.g., walking and running), sports performances (e.g., squatting) and work-related tasks (e.g., load lifting). These muscles control trunk stability via appropriate contraction (Watanabe et al., 2013) and are often classified into two major groups: the global or superficial muscles (e.g., erector spine) which are better adapted to the overall spinal movement because of their large size, and the local or profound muscles (e.g., internal oblique and multifidus) which are better suited as spine stabilizer because of placing closer to the center of rotation of spinal movements at appropriate angles (Ershad et al., 2009). To protect the spine structure from injury, activation of trunk muscles must be optimally timed with sufficient magnitude (Bonato et al., 2003) and highly coordinated with together (Anders et al., 2005). Besides, trunk muscle co-contraction, showing concurrent contraction of agonist-antagonist muscles, produces higher stability for trunk area with minor or no joint movements (Karimi et al., 2017).
Today low back pain (LBP) is one of the most common and costly musculoskeletal disorders (Watanabe et al., 2014), having a prevalence of 25 times higher in the industrial countries (Shabat et al., 2005). Among many work-related tasks, load lifting has been introduced as the most common cause of work-related LBP (Chow et al., 2005), probably because of putting high mechanical loads on musculoskeletal structures in the lower back area (Looze et al., 2000). Some studies showed that the activity pattern of trunk muscles during load lifting is associated with a high risk of LBP (Suehiro et al., 2018), and LBP patients demonstrate differences in the activity pattern of trunk muscles compared to healthy groups (Silfies et al., 2005). For example, previous studies reported that LBP patients have delay in the onset time of some local muscles (e.g., transversus abdominis) (Watanabe et al., 2013; Suehiro et al., 2018), attenuation in the activity of global back muscles (Watanabe et al., 2013; Suehiro et al., 2018), alteration in abdominal recruitment pattern causing less spine stability (Ershad et al., 2009), incorrect co-ordination of local muscles (Anders et al., 2005), higher activation of antagonistic muscles causing higher spine loading (Marras et al., 2004), alterations in recruitment pattern of trunk muscles (Suehiro et al., 2018), higher activation of global and lower activation of local abdominal muscles (Ershad et al., 2009) and higher peak activation causing overload and injury of spinal tissues (Heiss et al., 2002).
Given the above, the assessment of trunk muscle activity is crucial in injury prevention or rehabilitation programs, especially in industrial or work environments. Although numerous studies have investigated risk factor or differences in LBP patients (Watanabe et al., 2013; Ershad et al., 2009; Chow et al., 2005; Suehiro et al., 2018; Silfies et al., 2005; Marras et al., 2004; Heiss et al., 2002; Schinkel-Ivy et al., 2013; Yoon et al., 2012), the effect of using some interventions (e.g., orthotic devices) have not been widely studied. Insoles, a custom and widely-used orthotic device, prevent or correct deformities and improve performance (Murley et al., 2009, 2010) or even help to treat LBP problem (Shabat et al., 2005). Insoles with various wedges can alter the position of the ankle and foot joints (Yung-Hui and Wei-Hsien, 2005). Murley et al. (2009) stated that any change in the foot position may influence on the activity of trunk muscles (Murley et al., 2009). Ghasemi et al. (2018) also showed that placing wooden wedges in the anterior and medial regions of the feet decreases the activity of quadriceps muscles during load lifting (Ghasemi et al., 2018). In return, Bird et al. (2003) showed that foot wedging doesn't change the activity of erector spine and gluteus medius muscles during walking (Bird et al., 2003). Mills et al. (2010) stated that various shapes of foot orthoses need to be more assessed (Mills et al., 2010). Also, Ntousis et al. (2013) showed that bilateral or unilateral foot protonation or supination doesn't affect the activity of trunk muscles during quiet standing (Ntousis et al., 2013). However, the methodology of previous studies has some deficits because they change the ankle and foot positions using wooden wedges which may have no practicality in real environments in spite of real insoles (Ghasemi et al., 2018; Edwards et al., 2008; Kongsgaard et al., 2006). The other limitations of previous studies examining the effect of foot position alterations are less attention to the activation and coordination of trunk muscles. As discussed earlier, the role of trunk muscles is essential during load lifting, and some of the EMG indices can identify the risk of LBP occurrence. Therefore, the aim of present study was to investigate immediate effects of using insoles with various wedges on activation and co-contraction indices of selected trunk muscles during load lifting.
Section snippets
Participants
Although power analysis software (G*power) calculated the sample size of at least 28 subjects (statistical power = 0.95, effect size = 0.25 and alpha level = 0.01), thirty (n = 30) able-bodied males (age: 22.9 ± 3.2 years, weight: 68.6 ± 6.3 kg, height: 178.1 ± 5.3 cm) participated in this study voluntarily. The subjects had no musculoskeletal disorders in the lower extremities or abnormal feet structure, ensured with the index of Williams and McClay (2000) (Williams and McClay, 2000), and they
The effect of various insole wedges on the normalized mean amplitude and normalized peak amplitude during load lifting
The effect of various insole wedges on the normalized mean amplitude and normalized peak amplitude indices of selected trunk muscles during load lifting: The result of ANOVA with repeated measure test showed significant differences for the normalized mean amplitude of the RA muscle between posterior and anterior-medial wedges (P = 0.001) (the assumption of sphericity violated: χ (Ershad et al., 2009) (35) = 107.925 with P = 0.001; Greenhouse-Geisser correction: F (4.269) = 2.871 with
Discussion
The aim of present study was to investigate the immediate effects of using insoles with various wedges on the activation and co-contraction indices of selected trunk muscles during load lifting. The result of present study showed that the normalized mean amplitude values significantly decreased for the RA muscle in the posterior compared to the anterior-medial wedge, and for the QL muscle in the posterior compared to the lateral wedge (P = 0.001). These findings are in accordance with the study
Conclusions
While using insole with various wedges during load lifting, these changes in the EMG indices of selected trunk muscles were observed: lower mean amplitude in the posterior wedge than anterior-medial wedge for the RA muscle and lateral wedge for the QL muscle, lower peak amplitude of the RA muscle in the posterior than anterior-medial wedge, lower median frequency of the LES muscle in anterior-medial than anterior-lateral wedges, lower RA/TES, RA/LES and RA/MU co-contraction indices in the
Limitations
The limitations of present study including no assessment of stability indices or using clinical treatment groups (e.g., LBP patients) are suggested to future studies to assess more precisely other outcomes or clinical relevance in different populations following the use of various insole wedges.
Funding
This work was supported by the Iran National Science Foundation (INSF) [96014308].
Declaration of competing interest
The authors declare that there is no conflict of interest.
Acknowledgements
The authors would like to thank all the participants who took part in this study.
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