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Influence of smartphone use on the median frequency of mastigatory and trapezius muscles in women - a Pilot study
Journal Pre-proof Influence of smartphone use on the median frequency of mastigatory and trapezius muscles in women - Pilot study Fabiana Foltran Mescollotto, Elisa Bizetti Pelai, Ester Moreira de Castro, Paulo Fernandes Pires, Taís Silva Ferreira, Delaine Rodrigues Bigaton PII:
S1360-8592(19)30227-X
DOI:
https://doi.org/10.1016/j.jbmt.2019.09.003
Reference:
YJBMT 1876
To appear in:
Journal of Bodywork & Movement Therapies
Received Date: 11 June 2019 Accepted Date: 2 September 2019
Please cite this article as: Mescollotto, F.F., Pelai, E.B., Moreira de Castro, E., Pires, P.F., Ferreira, T.S., Bigaton, D.R., Influence Of Smartphone Use On The Median Frequency Of Mastigatory And Trapezius Muscles In Women - Pilot Study, Journal of Bodywork & Movement Therapies, https://doi.org/10.1016/ j.jbmt.2019.09.003. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Ltd.
INFLUENCE OF SMARTPHONE USE ON THE MEDIAN FREQUENCY OF MASTIGATORY AND TRAPEZIUS MUSCLES IN WOMEN - PILOT STUDY
Smartphone use on masticatory and trapezius muscles PhD Fabiana Foltran Mescollotto1, Ms Elisa Bizetti Pelai1, Ms Ester Moreira de Castro1, PhD Paulo Fernandes Pires2, Taís Silva Ferreira2, PhD Delaine Rodrigues Bigaton1
1
Pos Graduate Program in Human Movement Sciences, Methodist University of Piracicaba UNIMEP - Piracicaba (SP), Brazil; 2Graduate in Physical Therapy in Methodist University of Piracicaba – UNIMEP – Piraciacaba (SP)
Corresponding author: Fabiana Foltran Mescollotto Graduate Program in Human Movement Sciences, Methodist University of Piracicaba, Rodovia do Açúcar, Km 156, Bloco 7, Sala 37, Taquaral, Piracicaba, SP, 13400-911, Brazil. E-mail address: [email protected]
ABSTRACT INTRODUCTION: The use of smartphones is growing every year and excessive use of this device can generate adverse physical and mental effects. AIM: This study aimed to evaluate the influence of smartphone use on the median frequency of the masticatory muscles and upper trapezius muscles in healthy women. METHOD: Six healthy young women were evaluated. All volunteers were submitted to a submaximal bite protocol to evaluate the masticatory muscles. In addition, the volunteers were submitted to a protocol of bilateral shoulder elevation, to a submaximal load, to evaluate the upper trapezius muscles. Both protocols were performed before and after a task using the smartphone for 30 minutes. Median frequency (MF) values were collected during the bite protocol and submaximal shoulder elevation. RESULTS: Data were analyzed by means of specific statistical tests. A statistically significant reduction in MF for all masticatory muscles was observed in the bilateral bite task when comparing pre and post smartphone use (p<0.005). A significant reduction in MF was also found for the right upper trapezius when comparing pre and post use of the smartphone in the shoulder elevation task (p=0.001). CONCLUSION: It appears that prolonged smartphone use may contribute to fatigue in the masticatory and upper trapezius muscles. Therefore, guidelines for smartphone users should include advice on the moderate use of this device. Keywords: Smartphone, Electromyography, Muscle fatigue
INTRODUCTION
Smartphones are considered one of the essential items of modern human life (Kim et al., 2016). Given their convenience and variety of functions, smartphones are widely popular, and the number of users is rapidly increasing, with more than 1.08 billion users across the globe (Mok et al., 2014). In Brazil, in 2016, data presented by the Brazilian Institute of Statistics and Geography (IBGE) (“IBGE :: Instituto Brasileiro de Geografia e Estatística,” n.d.) showed that 138 million people possessed a smartphone with the highest numbers in the population between 25 and 34 years of age, where 88.6% had a smartphone. The rapid growth in the frequency of smartphone use in the population has generated both mental adverse effects, such as depression, anxiety, and changes in sleep quality (Ho et al., 2014), as well as physical alterations such as changes in neck musculature (Berolo et al., 2011).Alterations in the cervical spine have been related to dysfunctions and symptoms in the orofacial region (Sforza et al., 2011). Several studies have related the positioning of the head during the activity of using the smartphone. Studies indicate that there is interdependence between the regions of the mandible and cervical spine, which has been extensively explored in the literature considering both postural, biomechanical, and neuroanatomic relationships (Armijo Olivo et al., 2006; Armijo-Olivo et al., 2011; La Touche et al., 2015). The static posture adopted during the use of the smartphone can generate overload of the neck muscles, increasing muscle fatigue (Kim and Koo, 2016). Muscle fatigue is a complex and multifaceted process involving decreased metabolic substrates, such as phosphocreatine and glycogen, changes in blood flow, and an increase in reactive oxygen species. It can be characterized as a reduction in the capacity of the muscle to produce strength or power during voluntary contractions, presenting peripheral or central alterations and adaptations, which can lead to muscular injuries (Allen et al., 2008; Toma et al.,
2018). In addition, localized muscle fatigue can lead to changes in joint stability, and a less stable joint may be both the cause and consequence of pain (Ariens et al., 2001). The muscle fatigue process can be analyzed based mainly on the interpretation of the muscle Surface Electromyographic (EMG) signal evaluated in the frequency domain, the median frequency signal parameter (MF EMG), or the average EMG frequency index obtained by means of the spectral density, which evaluates the frequency of the motor units (De Luca, 1997) and shows a change in the values of these parameters at low frequencies, representing a reduction in the speed of conduction of muscle fibers (Xu et al., 2017). Muscle fatigue during smartphone use has been studied considering several muscles of the neck region (Choi et al., 2016, 2015; Kim and Koo, 2016). However, little is known about this subject, due to the scarcity of studies published and the low methodological quality of studies available in the literature on the subject. In addition, no studies were found that analyzed the head and neck relationship and its implications on the development of muscular fatigue during smartphone use. Therefore, this study is justified by the growing use of smartphones as well as the scarcity of studies in this area. We hypothesized that prolonged use of the smartphone may lead to fatigue in the upper trapezius and masticatory muscles. Thus, the present study aimed to evaluate the influence of smartphone use on muscular fatigue of the masticatory and upper trapezius muscles in healthy women.
MATERIALS AND METHODS
Study design and ethical aspects This is a pilot study with a cross-sectional observational design. The study was approved by the Research Ethics Committee of a University in the interior of São Paulo State under protocol no 2.004.097. All the volunteers signed the Consent Form.
Subjects The present study evaluated 6 healthy women with a mean age of 23 years, weight of 53.4 kg, and height of 1.65 meters. All the volunteers were recruited from a Methodist University of Piracicaba, in the interior of São Paulo State. The inclusion criteria were: female, 18 to 40 years
of age, no neck pain in the previous 30 days, and a body mass index (BMI) less than 25 kg/ m2. Women with pain in the orofacial region, who were under orthodontic or physiotherapeutic treatment, and who did not use social networks were excluded. Volunteers were asked about hand dominance at the moment of collection, in order to compare the results found.
Procedures An EMG 830C 8-channel acquisition module (EMG System do Brasil, São José dos Campos, Brazil) was used to collect EMG signals at a sampling frequency of 2000 Hz per channel. Six circular differentials (self-adhesive composed of Ag/AgCl with a 1 cm diameter and 20 mm inter-electrode center-to-center spacing, associated with conductive gel) were used with 20 times preamplification, totaling an amplification of 1000 times, IRMC> 100 dB, input impedance> 10 MΩ, and signal to noise ratio ≤3 µV. The self-adhesive reference monopolar electrode (composed of Ag/AgCl, 1 cm in diameter and associated with conductive gel) was placed on the manubrium of the sternum bone. The bipolar electrodes were positioned on the ventricles of the masseter and anterior temporal muscles bilaterally, and to confirm the positioning of the electrodes, muscular function was requested. The electrodes of the upper trapezius muscle were positioned half way along a line drawn between the acromion and the C7 spinous process (Surface Electromyography for the Non-Invasive Assessment of Muscles - SENIAM) (“Welcome to SENIAM,” n.d.). Before fixation of the electrodes, the skin was cleaned with cotton soaked in 70% alcohol solution and trichotomized and sanded. For the electromyographic evaluation of the masticatory muscles, the volunteers remained seated in a chair with their backs supported, feet parallel resting on the floor on a rubber mat, and arms resting on the front of the thighs (Frankfurt plane parallel to the ground). In this position the volunteers were asked to tighten the maxillary molar bite dynamometer for 5 seconds, repeated twice (Figure 1). Next, they performed submaximal tightening at 50% of the maximum load of maximal tightening for 30 seconds with two replicates. Between each clenching there was a rest interval of 3 minutes in order not to cause fatigue through the examination. This protocol was performed before and after using the smartphone.
PLACE FIGURE 1 HERE
For the electromyographic evaluation of the upper trapezius muscle the volunteers remained standing, on a wooden platform, with the arms alongside the body. In this position the volunteers were required to perform a shoulder lift movement holding a tension and compression load cell (Figure 2) and were stimulated to perform maximum force of the side being evaluated for 5 seconds, with two repetitions. This procedure was performed for both sides. The volunteers then performed the shoulder lift with a submaximal load, 70% of the maximum load, for 30 seconds, also twice. Between each movement there was a rest interval of 3 minutes, to avoid fatigue of the muscles caused by the evaluation. This protocol was performed before and after using the smartphone.
PLACE FIGURE 2 HERE
For the task of using the smartphone, the volunteers remained seated in a chair, with a backrest to the low back and the feet parallel resting on the ground on a rubber mat. The volunteers performed this activity for 30 minutes. During this period the volunteers were instructed not to communicate verbally, only through social networks and messaging applications.
Data processing EMG data were processed offline using Matlab® software 8.5.0.1976.13 (R2015a, MathWorks Inc., Natick, Massachusetts, USA). For the processing of the EMG signal, a 4th order Butterworth type digital filter with zero phase delay, high pass of 10 Hz and low pass of 400 Hz was applied. The first and last second of each EMG signal was always eliminated in order to avoid any interference that occurred at the beginning and end of each collection. The EMG signal was processed in the time domain to determine the median frequency (MF) values for evaluation of the magnitude of the electrical activity of the masticatory muscles during rest. For data analysis, the electromyographic signal obtained during the 30 seconds of submaximal contraction was divided into 5 windows. For each window the value of MF was obtained.
Statistical analysis
To test the normality of the data the Shapiro-Wilk test was performed. Subsequently, for the comparison before and after the use of the smartphone, the T-test for paired samples was used. In this analysis, the MF value of the first window of the submaximal contraction and the last window of the submaximal contraction after the use of the smartphone were used. SPSS 17.0 software (Chicago, IL) was utilized for the analyses, stipulating the value of 5% (p <0.05) for significance. The test power was calculated for the right upper trapezius in the right shoulder (pre: 88.8±16.0; post: 73.0±11.0) and a value of 0.802 was found. G Power software (Faul et al., 2007) was used to calculate the test power.
RESULTS The results of pre and post smartphone use through MF comparisons are presented in Tables 1 and 2. Table 1 shows that in the bilateral bite task there was a statistically significant difference in MF between the pre and post smartphone use for the masticatory muscles. For all the masticatory muscles, there was a reduction in MF when comparing the pre and post conditions. There was no statistically significant difference in MF of the upper trapezius muscle bilaterally.
PLACE TABLE 1 HERE
Table 2 shows that for the right shoulder elevation activity there was a statistically significant difference in MF of the right upper trapezius muscle between the pre and post smartphone use conditions. For this activity, there was a decrease in the MF from the pre to the post condition for the right upper trapezius muscle. There was no statistically significant difference for the activity of left shoulder elevation in any of the evaluated muscles.
PLACE TABLE 2 HERE
DISCUSSION The present study evaluated the influence of smartphone use on muscle fatigue of the masticatory (temporal and masseter bilateral) and upper trapezius muscles (bilateral) using the MF values, in healthy women. The results showed that there was a significant difference in MF of the masticatory muscles during a bilateral bite activity before and after the use of the
smartphone, indicating an increase in muscle fatigue levels after this activity. There was also a significant difference in MF of the right upper trapezius muscle during the right shoulder elevation activity before and after the use of the smartphone, indicating an increase in muscle fatigue levels after this activity. The results of the present study indicate that there was fatigue in the masticatory muscles after smartphone use. A possible hypothesis for these findings may be related to parafunctional activities. Parafunction refers to behaviors that are different from those required or associated with physiological functions such as chewing, communication, swallowing, or breathing (Khawaja et al., 2015). Studies have pointed to an association between these parafunctional behaviors and biopsychosocial characteristics, such as psychological (Khawaja et al., 2015) and physical symptoms (increased muscular tension). Therefore, during the use of the smartphone, which involves concentration and access to various types of information that can generate different psychological symptoms, the volunteers may have unconsciously performed parafunctional behaviors, which could have generated fatigue in the masticatory muscles, since parafunctional behaviors can lead to increased muscle tension and, thus, fatigue (Glaros et al., 2005). Another hypothesis is related to static posture, which is one of the important risk factors for smartphone users. The static posture adopted during the use of the smartphone leads to abnormal alignments of the neck and shoulder region (Kim and Koo, 2016). These abnormal alignments generate overload of the neck muscles, increasing muscle fatigue and decreasing functional capacity (Kim and Koo, 2016). Alterations in the cervical spine have been related to dysfunctions and symptoms in the orofacial region (Sforza et al., 2011). Several authors have studied the posture of the head as a possible factor related to temporomandibular disorders (TMD) (Armijo-Olivo et al., 2011; Nicolakis et al., 2000; Solow and Sandham, 2002). As a result, it is believed that there is interdependence between the orofacial structures and the neck, since lesions or diseases in one area can induce dysfunction and pain in the other (Browne et al., 1998), and neck pain is associated with the development of fatigue and muscle tension (Choi et al., 2016, 2015; Kim and Koo, 2016) in the muscles of this region. It is known that the cervical spine exerts great influence on the orofacial muscles (Sforza et al., 2011) and that, therefore, alterations in the cervical spine can lead to dysfunctions of the orofacial muscles (Browne et al., 1998). In addition, the angle of cervical flexion may influence
the muscle fatigue of the neck muscles, especially the trapezius (Lee et al., 2017). Thus, the neck flexion posture adopted during smartphone use may have generated muscular changes in the muscles of the face, justifying the appearance of fatigue found in the masticatory muscles. The results also demonstrated that there was a statistically significant difference in the activity of elevation of the right shoulder in the MF of the upper right trapezius muscle, after the use of the smartphone, indicative of muscular fatigue. The difference found only for the activity of right shoulder elevation could be related to the dominance of the volunteers, as 83.3% (5) were righthanded. Thus, during the use of the smartphone the volunteers, due to dominance, used the right upper limb more, a fact that may have generated fatigue in this muscle. Other studies have found a reduction in MF of the right trapezius muscle after 30-minutes use of the smartphone (Kim and Koo, 2016). Park et al. (Bae and Park, 2013) found a reduction in MF in the trapezius muscle bilaterally after a 20 minute smartphone activity. In the same study, the authors reported a higher load on the right shoulder when compared to the left shoulder, since the right shoulder region is used more frequently. The reduction in MF in the upper trapezius muscle, found in the present study and, also in other studies, is indicative of muscle fatigue in this muscle after the use of the smartphone. This may occur due to the cervical posture adopted during the use of the smartphone that involves the neck flexion in a static posture. It is known that the angle of cervical flexion is associated with muscular fatigue of the trapezius region (Lee et al., 2017). In addition, maintaining a static posture leads to misalignment of the neck and shoulder regions, which may lead to a greater burden on the neck muscles, generating fatigue and other alterations in the musculoskeletal system (Mekhora et al., 2000).
Limitations of the study Some limitations need to be considered. The first is related to the small sample size. However, the test power value was 0.802 which indicates that even though the sample size is small, it enables detection of statistical differences. The other limitation is that only female participants were recruited. This is because the prevalence of symptoms in the temporomandibular region (i.e., pain, limited range of motion, crepitus) is larger in women than men (2:1) (Lora et al., 2016). For future studies it is very important to evaluate both sexes. Another limitation is that the investigator was not blinded to the study purpose. The study did not actually measure muscle
activity and posture during smartphone use, because it is a pilot study, our research group is working in another study in order to do this evaluation.
Research applications It is suggested that future studies of high methodological quality be performed to evaluate the use of smartphones and muscular fatigue of the masticatory and trapezius muscles in individuals with different sides of dominance, in a larger population and possibly to determine the minimal duration of use before onset of muscle fatigue. This is important to define preventive measures.
CONCLUSION It appears that prolonged use of the smartphone may contribute to muscular fatigue in the masticatory (masseter and temporal) and right upper trapezius muscles in a sample of predominantly right-hand dominant participants. Therefore, guidelines for smartphone users should include its use in moderation and adoption of an appropriate posture while using the device. Clinical relevance •
Prolonged use of smartphone can contribute to muscular fatigue in masticatory muscles;
•
Prolonged use of smartphone can contribute to muscular fatigue in upper trapezius muscles (in dominant side);
•
Clinical professionals should observe and advise, the posture adopted during use of the smartphone and also on its overuse, to prevent possible damage caused by muscle fatigue.
ACKNOWLEDGE The authors would like to thank all the subjects who participated in this study. This work was funded by grants from Comissão de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Brasília, DF, Brazil.
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Table 1. The MF values (mean ± standard deviation) and level of significance (p) for the different muscles in the bilateral bite task pre and post a task using a smartphone. BILATERAL BITE Muscle
Pre
Post
p
Left Temporalis
138.1±12.7
128.4±11.6
0.001*
Left Masseter
140.9±9.0
127.4±17.3
0.025*
Right Temporalis
138.6±14.7
125.0±10.5
0.000*
Right Masseter
144.0±12.4
133.1±18.8
0.019*
Left Upper Trapezius
94.8±21.1
91.3±37.0
0.688
Right Upper Trapezius
75.8±25.5
89.3±45.0
0.266
* Significant difference between pre and post conditions (p <0.005).
Table 2. The MF values (mean ± standard deviation) and level of significance (p) for the different muscles in the task of elevating the right shoulder and elevating the left shoulder, before and after a task using a smartphone. RIGHT SHOULDER Muscle
LEFT SHOULDER
Pre
Post
p
Left Temporalis
103.0±25.8
107.5±25.0
0.58
118.0±36.9 116.6±40.4
0.64
Left Masseter
117.5±35.1
103.0±19.7
0.24
112.4±41.2 107.9±28.7
0.62
Right Temporalis
120.9±37.0
112.6±27.0
0.49
125.1±39.4 115.2±31.1
0.45
Right Masseter
113.1±±45.9
94.7±27.1
0.21
117.1±36.0 103.6±37.8
0.37
85.1±9.7
83.3±12.4
0.55
88.3±12.8
87.2±9.24
0.60
88.8±16.0
73.0±11.0
0.001*
82.5±11.5
85.2±16.2
0.23
Left Upper
Pre
Post
p
Trapezius Right Upper Trapezius * Significant difference between pre and post conditions (p <0.005).
Figure 1 - Positioning of volunteers during maximal tightening in the bilateral bite dynamometer. a) Anterior view; b) Side View.
Figure 2 - Positioning for the data collection with the tension and compression load cell for maximal and submaximal voluntary contraction of the upper trapezius muscles. a) Evaluation of the left upper trapezius; b) Evaluation of the right upper trapezius.
S1360-8592(19)30227-X
DOI:
https://doi.org/10.1016/j.jbmt.2019.09.003
Reference:
YJBMT 1876
To appear in:
Journal of Bodywork & Movement Therapies
Received Date: 11 June 2019 Accepted Date: 2 September 2019
Please cite this article as: Mescollotto, F.F., Pelai, E.B., Moreira de Castro, E., Pires, P.F., Ferreira, T.S., Bigaton, D.R., Influence Of Smartphone Use On The Median Frequency Of Mastigatory And Trapezius Muscles In Women - Pilot Study, Journal of Bodywork & Movement Therapies, https://doi.org/10.1016/ j.jbmt.2019.09.003. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Ltd.
INFLUENCE OF SMARTPHONE USE ON THE MEDIAN FREQUENCY OF MASTIGATORY AND TRAPEZIUS MUSCLES IN WOMEN - PILOT STUDY
Smartphone use on masticatory and trapezius muscles PhD Fabiana Foltran Mescollotto1, Ms Elisa Bizetti Pelai1, Ms Ester Moreira de Castro1, PhD Paulo Fernandes Pires2, Taís Silva Ferreira2, PhD Delaine Rodrigues Bigaton1
1
Pos Graduate Program in Human Movement Sciences, Methodist University of Piracicaba UNIMEP - Piracicaba (SP), Brazil; 2Graduate in Physical Therapy in Methodist University of Piracicaba – UNIMEP – Piraciacaba (SP)
Corresponding author: Fabiana Foltran Mescollotto Graduate Program in Human Movement Sciences, Methodist University of Piracicaba, Rodovia do Açúcar, Km 156, Bloco 7, Sala 37, Taquaral, Piracicaba, SP, 13400-911, Brazil. E-mail address: [email protected]
ABSTRACT INTRODUCTION: The use of smartphones is growing every year and excessive use of this device can generate adverse physical and mental effects. AIM: This study aimed to evaluate the influence of smartphone use on the median frequency of the masticatory muscles and upper trapezius muscles in healthy women. METHOD: Six healthy young women were evaluated. All volunteers were submitted to a submaximal bite protocol to evaluate the masticatory muscles. In addition, the volunteers were submitted to a protocol of bilateral shoulder elevation, to a submaximal load, to evaluate the upper trapezius muscles. Both protocols were performed before and after a task using the smartphone for 30 minutes. Median frequency (MF) values were collected during the bite protocol and submaximal shoulder elevation. RESULTS: Data were analyzed by means of specific statistical tests. A statistically significant reduction in MF for all masticatory muscles was observed in the bilateral bite task when comparing pre and post smartphone use (p<0.005). A significant reduction in MF was also found for the right upper trapezius when comparing pre and post use of the smartphone in the shoulder elevation task (p=0.001). CONCLUSION: It appears that prolonged smartphone use may contribute to fatigue in the masticatory and upper trapezius muscles. Therefore, guidelines for smartphone users should include advice on the moderate use of this device. Keywords: Smartphone, Electromyography, Muscle fatigue
INTRODUCTION
Smartphones are considered one of the essential items of modern human life (Kim et al., 2016). Given their convenience and variety of functions, smartphones are widely popular, and the number of users is rapidly increasing, with more than 1.08 billion users across the globe (Mok et al., 2014). In Brazil, in 2016, data presented by the Brazilian Institute of Statistics and Geography (IBGE) (“IBGE :: Instituto Brasileiro de Geografia e Estatística,” n.d.) showed that 138 million people possessed a smartphone with the highest numbers in the population between 25 and 34 years of age, where 88.6% had a smartphone. The rapid growth in the frequency of smartphone use in the population has generated both mental adverse effects, such as depression, anxiety, and changes in sleep quality (Ho et al., 2014), as well as physical alterations such as changes in neck musculature (Berolo et al., 2011).Alterations in the cervical spine have been related to dysfunctions and symptoms in the orofacial region (Sforza et al., 2011). Several studies have related the positioning of the head during the activity of using the smartphone. Studies indicate that there is interdependence between the regions of the mandible and cervical spine, which has been extensively explored in the literature considering both postural, biomechanical, and neuroanatomic relationships (Armijo Olivo et al., 2006; Armijo-Olivo et al., 2011; La Touche et al., 2015). The static posture adopted during the use of the smartphone can generate overload of the neck muscles, increasing muscle fatigue (Kim and Koo, 2016). Muscle fatigue is a complex and multifaceted process involving decreased metabolic substrates, such as phosphocreatine and glycogen, changes in blood flow, and an increase in reactive oxygen species. It can be characterized as a reduction in the capacity of the muscle to produce strength or power during voluntary contractions, presenting peripheral or central alterations and adaptations, which can lead to muscular injuries (Allen et al., 2008; Toma et al.,
2018). In addition, localized muscle fatigue can lead to changes in joint stability, and a less stable joint may be both the cause and consequence of pain (Ariens et al., 2001). The muscle fatigue process can be analyzed based mainly on the interpretation of the muscle Surface Electromyographic (EMG) signal evaluated in the frequency domain, the median frequency signal parameter (MF EMG), or the average EMG frequency index obtained by means of the spectral density, which evaluates the frequency of the motor units (De Luca, 1997) and shows a change in the values of these parameters at low frequencies, representing a reduction in the speed of conduction of muscle fibers (Xu et al., 2017). Muscle fatigue during smartphone use has been studied considering several muscles of the neck region (Choi et al., 2016, 2015; Kim and Koo, 2016). However, little is known about this subject, due to the scarcity of studies published and the low methodological quality of studies available in the literature on the subject. In addition, no studies were found that analyzed the head and neck relationship and its implications on the development of muscular fatigue during smartphone use. Therefore, this study is justified by the growing use of smartphones as well as the scarcity of studies in this area. We hypothesized that prolonged use of the smartphone may lead to fatigue in the upper trapezius and masticatory muscles. Thus, the present study aimed to evaluate the influence of smartphone use on muscular fatigue of the masticatory and upper trapezius muscles in healthy women.
MATERIALS AND METHODS
Study design and ethical aspects This is a pilot study with a cross-sectional observational design. The study was approved by the Research Ethics Committee of a University in the interior of São Paulo State under protocol no 2.004.097. All the volunteers signed the Consent Form.
Subjects The present study evaluated 6 healthy women with a mean age of 23 years, weight of 53.4 kg, and height of 1.65 meters. All the volunteers were recruited from a Methodist University of Piracicaba, in the interior of São Paulo State. The inclusion criteria were: female, 18 to 40 years
of age, no neck pain in the previous 30 days, and a body mass index (BMI) less than 25 kg/ m2. Women with pain in the orofacial region, who were under orthodontic or physiotherapeutic treatment, and who did not use social networks were excluded. Volunteers were asked about hand dominance at the moment of collection, in order to compare the results found.
Procedures An EMG 830C 8-channel acquisition module (EMG System do Brasil, São José dos Campos, Brazil) was used to collect EMG signals at a sampling frequency of 2000 Hz per channel. Six circular differentials (self-adhesive composed of Ag/AgCl with a 1 cm diameter and 20 mm inter-electrode center-to-center spacing, associated with conductive gel) were used with 20 times preamplification, totaling an amplification of 1000 times, IRMC> 100 dB, input impedance> 10 MΩ, and signal to noise ratio ≤3 µV. The self-adhesive reference monopolar electrode (composed of Ag/AgCl, 1 cm in diameter and associated with conductive gel) was placed on the manubrium of the sternum bone. The bipolar electrodes were positioned on the ventricles of the masseter and anterior temporal muscles bilaterally, and to confirm the positioning of the electrodes, muscular function was requested. The electrodes of the upper trapezius muscle were positioned half way along a line drawn between the acromion and the C7 spinous process (Surface Electromyography for the Non-Invasive Assessment of Muscles - SENIAM) (“Welcome to SENIAM,” n.d.). Before fixation of the electrodes, the skin was cleaned with cotton soaked in 70% alcohol solution and trichotomized and sanded. For the electromyographic evaluation of the masticatory muscles, the volunteers remained seated in a chair with their backs supported, feet parallel resting on the floor on a rubber mat, and arms resting on the front of the thighs (Frankfurt plane parallel to the ground). In this position the volunteers were asked to tighten the maxillary molar bite dynamometer for 5 seconds, repeated twice (Figure 1). Next, they performed submaximal tightening at 50% of the maximum load of maximal tightening for 30 seconds with two replicates. Between each clenching there was a rest interval of 3 minutes in order not to cause fatigue through the examination. This protocol was performed before and after using the smartphone.
PLACE FIGURE 1 HERE
For the electromyographic evaluation of the upper trapezius muscle the volunteers remained standing, on a wooden platform, with the arms alongside the body. In this position the volunteers were required to perform a shoulder lift movement holding a tension and compression load cell (Figure 2) and were stimulated to perform maximum force of the side being evaluated for 5 seconds, with two repetitions. This procedure was performed for both sides. The volunteers then performed the shoulder lift with a submaximal load, 70% of the maximum load, for 30 seconds, also twice. Between each movement there was a rest interval of 3 minutes, to avoid fatigue of the muscles caused by the evaluation. This protocol was performed before and after using the smartphone.
PLACE FIGURE 2 HERE
For the task of using the smartphone, the volunteers remained seated in a chair, with a backrest to the low back and the feet parallel resting on the ground on a rubber mat. The volunteers performed this activity for 30 minutes. During this period the volunteers were instructed not to communicate verbally, only through social networks and messaging applications.
Data processing EMG data were processed offline using Matlab® software 8.5.0.1976.13 (R2015a, MathWorks Inc., Natick, Massachusetts, USA). For the processing of the EMG signal, a 4th order Butterworth type digital filter with zero phase delay, high pass of 10 Hz and low pass of 400 Hz was applied. The first and last second of each EMG signal was always eliminated in order to avoid any interference that occurred at the beginning and end of each collection. The EMG signal was processed in the time domain to determine the median frequency (MF) values for evaluation of the magnitude of the electrical activity of the masticatory muscles during rest. For data analysis, the electromyographic signal obtained during the 30 seconds of submaximal contraction was divided into 5 windows. For each window the value of MF was obtained.
Statistical analysis
To test the normality of the data the Shapiro-Wilk test was performed. Subsequently, for the comparison before and after the use of the smartphone, the T-test for paired samples was used. In this analysis, the MF value of the first window of the submaximal contraction and the last window of the submaximal contraction after the use of the smartphone were used. SPSS 17.0 software (Chicago, IL) was utilized for the analyses, stipulating the value of 5% (p <0.05) for significance. The test power was calculated for the right upper trapezius in the right shoulder (pre: 88.8±16.0; post: 73.0±11.0) and a value of 0.802 was found. G Power software (Faul et al., 2007) was used to calculate the test power.
RESULTS The results of pre and post smartphone use through MF comparisons are presented in Tables 1 and 2. Table 1 shows that in the bilateral bite task there was a statistically significant difference in MF between the pre and post smartphone use for the masticatory muscles. For all the masticatory muscles, there was a reduction in MF when comparing the pre and post conditions. There was no statistically significant difference in MF of the upper trapezius muscle bilaterally.
PLACE TABLE 1 HERE
Table 2 shows that for the right shoulder elevation activity there was a statistically significant difference in MF of the right upper trapezius muscle between the pre and post smartphone use conditions. For this activity, there was a decrease in the MF from the pre to the post condition for the right upper trapezius muscle. There was no statistically significant difference for the activity of left shoulder elevation in any of the evaluated muscles.
PLACE TABLE 2 HERE
DISCUSSION The present study evaluated the influence of smartphone use on muscle fatigue of the masticatory (temporal and masseter bilateral) and upper trapezius muscles (bilateral) using the MF values, in healthy women. The results showed that there was a significant difference in MF of the masticatory muscles during a bilateral bite activity before and after the use of the
smartphone, indicating an increase in muscle fatigue levels after this activity. There was also a significant difference in MF of the right upper trapezius muscle during the right shoulder elevation activity before and after the use of the smartphone, indicating an increase in muscle fatigue levels after this activity. The results of the present study indicate that there was fatigue in the masticatory muscles after smartphone use. A possible hypothesis for these findings may be related to parafunctional activities. Parafunction refers to behaviors that are different from those required or associated with physiological functions such as chewing, communication, swallowing, or breathing (Khawaja et al., 2015). Studies have pointed to an association between these parafunctional behaviors and biopsychosocial characteristics, such as psychological (Khawaja et al., 2015) and physical symptoms (increased muscular tension). Therefore, during the use of the smartphone, which involves concentration and access to various types of information that can generate different psychological symptoms, the volunteers may have unconsciously performed parafunctional behaviors, which could have generated fatigue in the masticatory muscles, since parafunctional behaviors can lead to increased muscle tension and, thus, fatigue (Glaros et al., 2005). Another hypothesis is related to static posture, which is one of the important risk factors for smartphone users. The static posture adopted during the use of the smartphone leads to abnormal alignments of the neck and shoulder region (Kim and Koo, 2016). These abnormal alignments generate overload of the neck muscles, increasing muscle fatigue and decreasing functional capacity (Kim and Koo, 2016). Alterations in the cervical spine have been related to dysfunctions and symptoms in the orofacial region (Sforza et al., 2011). Several authors have studied the posture of the head as a possible factor related to temporomandibular disorders (TMD) (Armijo-Olivo et al., 2011; Nicolakis et al., 2000; Solow and Sandham, 2002). As a result, it is believed that there is interdependence between the orofacial structures and the neck, since lesions or diseases in one area can induce dysfunction and pain in the other (Browne et al., 1998), and neck pain is associated with the development of fatigue and muscle tension (Choi et al., 2016, 2015; Kim and Koo, 2016) in the muscles of this region. It is known that the cervical spine exerts great influence on the orofacial muscles (Sforza et al., 2011) and that, therefore, alterations in the cervical spine can lead to dysfunctions of the orofacial muscles (Browne et al., 1998). In addition, the angle of cervical flexion may influence
the muscle fatigue of the neck muscles, especially the trapezius (Lee et al., 2017). Thus, the neck flexion posture adopted during smartphone use may have generated muscular changes in the muscles of the face, justifying the appearance of fatigue found in the masticatory muscles. The results also demonstrated that there was a statistically significant difference in the activity of elevation of the right shoulder in the MF of the upper right trapezius muscle, after the use of the smartphone, indicative of muscular fatigue. The difference found only for the activity of right shoulder elevation could be related to the dominance of the volunteers, as 83.3% (5) were righthanded. Thus, during the use of the smartphone the volunteers, due to dominance, used the right upper limb more, a fact that may have generated fatigue in this muscle. Other studies have found a reduction in MF of the right trapezius muscle after 30-minutes use of the smartphone (Kim and Koo, 2016). Park et al. (Bae and Park, 2013) found a reduction in MF in the trapezius muscle bilaterally after a 20 minute smartphone activity. In the same study, the authors reported a higher load on the right shoulder when compared to the left shoulder, since the right shoulder region is used more frequently. The reduction in MF in the upper trapezius muscle, found in the present study and, also in other studies, is indicative of muscle fatigue in this muscle after the use of the smartphone. This may occur due to the cervical posture adopted during the use of the smartphone that involves the neck flexion in a static posture. It is known that the angle of cervical flexion is associated with muscular fatigue of the trapezius region (Lee et al., 2017). In addition, maintaining a static posture leads to misalignment of the neck and shoulder regions, which may lead to a greater burden on the neck muscles, generating fatigue and other alterations in the musculoskeletal system (Mekhora et al., 2000).
Limitations of the study Some limitations need to be considered. The first is related to the small sample size. However, the test power value was 0.802 which indicates that even though the sample size is small, it enables detection of statistical differences. The other limitation is that only female participants were recruited. This is because the prevalence of symptoms in the temporomandibular region (i.e., pain, limited range of motion, crepitus) is larger in women than men (2:1) (Lora et al., 2016). For future studies it is very important to evaluate both sexes. Another limitation is that the investigator was not blinded to the study purpose. The study did not actually measure muscle
activity and posture during smartphone use, because it is a pilot study, our research group is working in another study in order to do this evaluation.
Research applications It is suggested that future studies of high methodological quality be performed to evaluate the use of smartphones and muscular fatigue of the masticatory and trapezius muscles in individuals with different sides of dominance, in a larger population and possibly to determine the minimal duration of use before onset of muscle fatigue. This is important to define preventive measures.
CONCLUSION It appears that prolonged use of the smartphone may contribute to muscular fatigue in the masticatory (masseter and temporal) and right upper trapezius muscles in a sample of predominantly right-hand dominant participants. Therefore, guidelines for smartphone users should include its use in moderation and adoption of an appropriate posture while using the device. Clinical relevance •
Prolonged use of smartphone can contribute to muscular fatigue in masticatory muscles;
•
Prolonged use of smartphone can contribute to muscular fatigue in upper trapezius muscles (in dominant side);
•
Clinical professionals should observe and advise, the posture adopted during use of the smartphone and also on its overuse, to prevent possible damage caused by muscle fatigue.
ACKNOWLEDGE The authors would like to thank all the subjects who participated in this study. This work was funded by grants from Comissão de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Brasília, DF, Brazil.
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Table 1. The MF values (mean ± standard deviation) and level of significance (p) for the different muscles in the bilateral bite task pre and post a task using a smartphone. BILATERAL BITE Muscle
Pre
Post
p
Left Temporalis
138.1±12.7
128.4±11.6
0.001*
Left Masseter
140.9±9.0
127.4±17.3
0.025*
Right Temporalis
138.6±14.7
125.0±10.5
0.000*
Right Masseter
144.0±12.4
133.1±18.8
0.019*
Left Upper Trapezius
94.8±21.1
91.3±37.0
0.688
Right Upper Trapezius
75.8±25.5
89.3±45.0
0.266
* Significant difference between pre and post conditions (p <0.005).
Table 2. The MF values (mean ± standard deviation) and level of significance (p) for the different muscles in the task of elevating the right shoulder and elevating the left shoulder, before and after a task using a smartphone. RIGHT SHOULDER Muscle
LEFT SHOULDER
Pre
Post
p
Left Temporalis
103.0±25.8
107.5±25.0
0.58
118.0±36.9 116.6±40.4
0.64
Left Masseter
117.5±35.1
103.0±19.7
0.24
112.4±41.2 107.9±28.7
0.62
Right Temporalis
120.9±37.0
112.6±27.0
0.49
125.1±39.4 115.2±31.1
0.45
Right Masseter
113.1±±45.9
94.7±27.1
0.21
117.1±36.0 103.6±37.8
0.37
85.1±9.7
83.3±12.4
0.55
88.3±12.8
87.2±9.24
0.60
88.8±16.0
73.0±11.0
0.001*
82.5±11.5
85.2±16.2
0.23
Left Upper
Pre
Post
p
Trapezius Right Upper Trapezius * Significant difference between pre and post conditions (p <0.005).
Figure 1 - Positioning of volunteers during maximal tightening in the bilateral bite dynamometer. a) Anterior view; b) Side View.
Figure 2 - Positioning for the data collection with the tension and compression load cell for maximal and submaximal voluntary contraction of the upper trapezius muscles. a) Evaluation of the left upper trapezius; b) Evaluation of the right upper trapezius.