Pain mechanisms in computer and smartphone users

Depósito de investigación de la Universidad de Sevilla https://idus.us.es/ Esta es la versión aceptada del capítulo publicado en: This is an accepted manuscript of a chapter published in: Features and Assessments of Pain, Anesthesia, and Analgesia (2021) DOI: 0.1016/B978-0-12-818988-7.00021-2 Copyright: © 2022 Elsevier Inc. All rights reserved. El acceso a la versión publicada del capítulo puede requerir la suscripción. Access to the published version may require subscription. “This is an Accepted Manuscript of an chapter published by Elsevier in Features and Assessments of Pain, Anaesthesia, and Analgesia on 2021, available at: https://doi.org/0.1016/B978-0-12-818988-7.00021-2.” UNCORRECTED PROOF Chapter 27 Pain mechanisms in computer and smartphone users Alberto Marcos Heredia-Rizoa, Pascal Madeleineband Grace P.Y. Szetoc aDepartment of Physiotherapy, Faculty of Nursing, Physiotherapy and Podiatry, University of Seville, Seville, Spain,bSport Sciences—Performance and Technology, Department of Health Science and Technology, Aalborg University, Aalborg, Denmark,cSchool of Medical and Health Sciences, Tung Wah College, Hong Kong, China Abbreviations LBP low-back pain MSD musculoskeletal disorder NP neck pain NSP neck-shoulder pain VDU visual display unit Introduction Over the last centuries, the nature of work has influenced the health condition of individuals. Musculoskeletal disorders (MSDs) represent one of the most common occupational problems worldwide (Hoe, Urquhart, Kelsall, Zamri, & Sim, 2018). The number of office workers has increased in the last decades, with approx. 57% of occupations requiring the use of visual display units (VDUs) (Parent-Thirion et al., 2017). Additionally, the trend is for people to spend longer periods of time with computers and smartphones, both at work and during leisure activities. The commonly used electronic devices include laptops and tablet computers in addition to desktop computers. Compared with other jobs, white-collar workers report the highest incidence (35%–60%) and annual prevalence (40%–70%) of neck-shoulder pain (NSP) (Hoe et al., 2018). Low-back pain (LBP) is also a frequent and disabling condition within this population, with a 1-year prevalence of 35%–40%, and an incidence rate at 14%–23% (Janwantanakul, Sihawong, Sitthipornvorakul, & Paksaichol, 2018). Most evidence indicates a higher prevalence in women, compared with men. This poses a serious burden due to reduced productivity (presenteeism), absenteeism from work, and use of health care resources (Bevan, 2015) (Fig. 1). In 2015, the total costs of work-related MSDs represented up to 2% of the gross domestic product in the European Union (approx. €240 billion annually), and involved 40 million workers (Bevan, 2015). Concomitant NSP and LBP increase the risk for long-term sickness absence by 75% in white-collar workers (Andersen, Mortensen, Hansen, & Burr, 2011), and 10% of them report reduced productivity due to occupational MSDs (Hagberg, Vilhemsson, Tornqvist, & Toomingas, 2007). The financial burden of musculoskeletal pain among computer users is estimated on average $AUD 1520 (€895) annually per person (Pereira et al., 2017). Job demands, level of satisfaction, and psychological distress are the causes that mostly influence productivity loss (Hagberg et al., 2007). The Neuroscience of Pain. https://doi.org/10.1016/B978-0-12-818988-7.00021-2 Copyright © 2021. 1 UNCORRECTED PROOF 2The Neuroscience of Pain FIG. 1 Burden of occupational neck-shoulder and low-back pain. Origins and mechanisms of neck-shoulder pain As pointed earlier, NSP is common in computer and smartphones users. The cervical spine and the shoulder joint are complex structures having a postural role, i.e., stabilization of the head and the shoulder girdle, and a functional role in the control of head and arm movements (Madeleine, 2010), necessary when using VDUs. The origin of NSP in MSDs is located in the deep structures around cartilage, tendons, ligaments, and muscles. Musculoskeletal pain is mediated by nociceptive-free nerve endings (Mense, 1993). Muscle nociceptors are located in the connective tissue, linked to primary afferent neurons, and are mostly polymodal, meaning that can, for instance, respond to mechanical and chemical stimuli. Biochemical changes, including altered oxidative metabolism and intramuscular microcirculation (Larsson, Björk, Kadi, Lindman, & Gerdle, 2004), and a higher accumulation of nociceptive substances after sustained and increased muscle load or activity (Rosendal et al., 2004), are reported in the presence of work-related trapezius myalgia. Such changes appear sufficient to activate peripheral nociception. The processing of nociceptive inputs via to the dorsal horn is only partially known. Wide dynamic range neurones located in the spinal cord respond to a large range of noxious and nonnoxious stimuli (Wagman & Price, 1969). A general central inhibition of the γ-motor neurones on agonist and antagonist muscles have been demonstrated in occupational pain syndromes (Johansson & Sojka, 1991). Peripheral and centrally mediated mechanisms play important roles in muscle pain development (Graven-Nielsen, 2006). Recurrent acute pain episodes may induce sensitization and lead to chronic work-related pain. However, chronic NSP among computer and smartphones users is still a matter of debate due to a lack of clear etiology of MSDs in general (Madeleine, 2008). Further, the relationship between occupational exposure and neck-shoulder disorders remains uncertain (Madeleine, Vangsgaard, Hviid Andersen, Ge, & Arendt-Nielsen, 2013). Overall, the excitability of the pain system is reported to be normal in computer users with low pain intensity. Only those with higher pain intensity and lower pressure pain thresholds have shown decreased efficiency in descending pain modulation (Ge, Vangsgaard, Omland, Madeleine, & Arendt-Nielsen, 2014;Heredia-Rizo, Petersen, Madeleine, & Arendt-Nielsen, 2019). These findings support the idea that chronic NSP can only be partly explained by an increased excitability of the pain system. Low-back pain mechanisms in computer and smartphone users Similar to NSP, our understanding of the pain mechanisms related to LBP is limited. Episodes of LBP result from a mix of personal and work-related physical or psychosocial exposure. Apparently, several behavioral patterns may predispose office workers to a higher prevalence of LBP. There is evidence of signs of central sensitization in nonspecific LBP (Den Bandt, Paulis, Beckwée, Ickmans, & Nijs, 2019). Further, altered pronociceptive and antinociceptive mechanisms, i.e., temporal summation of pain and conditioned pain modulation, are present in LBP patients and related to pain severity UNCORRECTED PROOF Chapter | 27 3 (McPhee, Vaegter, & Graven-Nielsen, 2020), although scarce research has focused on office workers. All in all, LBP results in adaptative changes impacting the working life of computer and smartphone users. Office, customer service and call center employees spend an average of 75% of their time seated (Thorp et al., 2012). This has been traditionally linked with increased low-back discomfort, reduced mobility, and with LBP onset. Yet, current evidence on the latter issue is controversial (Bontrup et al., 2019). Although too much sitting is a health concern, the transition to sit/stand workstation resulting in prolonged occupational standing has also been associated with the occurrence of LBP (Coenen et al., 2018). Computer users with nonspecific LBP demonstrate lower flexor and extensor trunk muscles endurance (del Pozo-Cruz et al., 2013), a more asymmetrical seated position, and less frequent postural shifts, compared with healthy workers (Akkarakittichoke & Janwantanakul, 2017). During sustained sitting, people with LBP show reduced temporal variability in the activation of the low-back muscles (Ringheim, Indahl, & Roeleveld, 2019), which could be a risk factor for intervertebral disk changes. Several mechanisms may contribute to the altered sensitivity, modified neuromuscular behavior, and LBP development associated with prolonged sitting. For example, previous LBP episodes, the frequency of breaks at work, an increased low-back muscle activity, and the soft tissue deformation induced by keeping a flexed spine position during long periods of time (Greene et al., 2019). However, no definite conclusions can be drawn due to the high variability of LBP presentations and modifying factors. Future research should investigate pain mechanisms and adaptations in subgroups of workers with LBP of similar clinical features. Individual risks factors Among the individual risk factors that affect the development of MSDs in computer and smartphone users, the most commonly examined may be sex/gender and age. A study on over 300 female computer users concluded that the individual factors linked with poorer neck disability were older age and higher body mass index (Johnston, Souvlis, Jimmieson, & Jull, 2008). Later, in a cohort study on office workers in Sudan, age and sex were considered confounding aspects for physical, i.e., workstation setting, and posture; as well as psychological risk factors, i.e., job strain and time pressure (Eltayeb, Staal, Khamis, & De Bie, 2011). In short, age, sex, and history of trauma are significantly associated with NSP onset in users of VDUs (Keown & Tuchin, 2018). A history of LBP is a strong predictor of the onset and chronification of LBP in this population, with inconclusive evidence for the role of age (Ye, Jing, Wei, & Lu, 2017). Individual physical capacity, expressed by muscle strength, endurance, and flexibility, has also been correlated with the occurrence of neck and low-back symptoms in office workers (Cabral, de Moreira, de Barros, & de Sato, 2019). Sex differences in MSDs have been demonstrated in white-collar employees. For example, Cho, Hwang, and Cherng (2012) observed a higher prevalence of neck symptoms in males, compared with females, whereas females showed higher rate of shoulder compared to neck pain (NP), although these findings are not consistent among studies. Similarly, women report higher NSP intensity, longer pain duration, and more pain locations, compared with men (Madeleine et al., 2013). Laboratory studies suggest that women tend to use higher forces relative to their maximum capacity to type on keyboards, which is related to their anthropometrics (Won, Johnson, Punnett, & Dennerlein, 2009). In the general population, systematic reviews have concurred that female sex, and older age (for men) are important risk factors for new onset of NP (Mc Lean et al., 2010), with no gender differences for LBP prevalence (Hoy, Brooks, Blyth, & Buchbinder, 2010). Interestingly, women report lower work-ability than men (Madeleine et al., 2013), underlining the complexity of integrating only age or sex/gender as individual factors when studying the impact of NSP and LBP in computer and smartphone users. Physical risks factors for the development of pain Workplace physical risk factors concerning computer workstation have been broadly investigated, including computer, keyboard and mouse use duration, and the workstation design, e.g., monitor, keyboard, and mouse location, chair height, sit/stand workstation, and arm support. Prolonged sedentary hours and worker posture are also considered important risk factors. Jun, Zoe, Johnston, and O’Leary (2017) presented the physical risk factors for computer-related NSP among office workers and concluded that keyboard position and low work task variation were predictors of NSP onset. The risk estimates for MSDs appear to be stronger for mouse use compared to keyboard and total computer use. In fact, increased risk of NSP has been associated with over 3–4 h of self-reported mouse use per day (Ijmker et al., 2011), with inconclusive evidence on this issue (Jun et al., 2017). The role of the speed and force of repetitive movements in performing keyboard typing and mouse work were investigated in a series of laboratory studies by Szeto, Straker, and O’Sullivan (2005a, 2005b, 2005c). These studies found that computer and smartphone users with NSP have increased neck muscle Pain in users of visual display units Chapter | 27 UNCORRECTED PROOF 4The Neuroscience of Pain activity during functional tasks (Szeto et al., 2005a;Xie, Szeto, Dai, & Madeleine, 2016) (Fig. 2). There is general agreement that providing arm support during keyboard work is important (Rempel et al., 2006). It is also recommended keeping the keyboard in front and maintaining the forearms and wrist joints in neutral positions to reduce the risk for neck-shoulder-arm symptoms (Jun et al., 2017). In terms of the display screen position, computer location (monitor not in front) is associated with NSP and LBP in office workers (Ye et al., 2017). Research has generally found that increased neck flexion angles due to a low screen position produces higher muscle activity to maintain the posture (Xie, Madeleine, Tsang, & Szeto, 2017) (Fig. 3). This is suggested to be a risk factor for NP development. For female office workers, the combination of poor working postures and job strain could predispose to LBP (Janwantanakul, Sitthipornvorakul, & Paksaichol, 2012). Prolonged standing computer work due to the use of sit/stand workstation can also result in LBP (Coenen et al., 2018). In conclusion, a relatively static flexion posture, sustained muscle activity, repetitive arm movements, and insufficient rest are the most known physical risk factors for occupational MSDs. However, majority of the research on this topic has FIG. 2 Muscle activity of neck-shoulder muscles comparing computer keyboard typing and smartphone texting in neck-shoulder pain patients and controls. APDF, amplitude probability distribution function; B-Text, bilateral smartphone texting; U-Text, unilateral texting; TYPE, computer keyboard typing. *Significant between-groups differences, *P< .05, **P< .01. FIG. 3 Median angles of spine flexion/extension comparing computer keyboard typing and smartphone texting in neck-shoulder pain patients and controls. B-Text, bilateral smartphone texting; TYPE, computer keyboard typing. *Significant between-groups differences, **P< .01. UNCORRECTED PROOF Chapter | 27 5 only produced limited evidence for the associated risk of physical factors involved with NSP and LBP (Jun et al., 2017; Ye et al., 2017). Psychosocial risks factors Stress, depressed mood, cognitive functioning, and pain behavior are well-known risk factors in NP and LBP in the general population (Linton, 2000). Work-related psychosocial risk aspects refer to the employee perception about how the work is planned, supervised, and conducted. Various studies have examined the role of these elements, i.e., mental stress, work pace, job autonomy and satisfaction, and support from others. A systematic review on the psychosocial factors on NSP concluded that job demands, job control and strain, and social support have a strong “incremental”effect on adding to the influence of physical risk factors to the development of NSP among office workers (Kraatz, Lang, Kraus, Münster, & Ochsmann, 2013). Most studies examined physical and psychosocial aspects (Janwantanakul et al., 2012); hence, it is difficult to differentiate the separate causal effects of these two domains. The time course of the interaction between psychological health and job-related behavior also needs to be investigated. There is conflicting level of evidence for self-perceived medium/high muscular tension as a risk factor for NSP in computer users (Wahlström, Lindegård, Ahlborg Jr., Ekman, & Hagberg, 2003). The phenomenon of perceived muscular tension may reflect an interactive process of physical and psychosocial stress underlining once again the complexity of NSP, although this is still to be explored. The role of other psychosocial aspects, such as job demands, low influence at work, and low satisfaction with the workplace, also remains controversial (Jun et al., 2017;Paksaichol, Janwantanakul, Purepong, Pensri, & Van Der Beek, 2012). This may be due to the large heterogeneity of studies in this field. Overall, the complex interrelations among internal and external risk factors emphasize the multimodality of work-re- lated MSDs (Fig. 4). The large number of risk factors and their potential relationships explains why when dealing with work-related disorders, one is confronted to heterogeneous patient groups with both diffuse (constant fatigue, stiffness, referred pain) and specific symptoms (increased muscle tone, painful locations, and trigger points). Physical activity to prevent and manage musculoskeletal pain in computer and smartphone users Treatment for occupational MSDs may focus on the workers’health status or on the job tasks and environment (Fig. 5). This section summarizes the current evidence on the efficacy of exercise interventions in computer and smartphone users. The idea is to restore balance between the workers ability and the work demand so the relative load is tipping on the safe side (Fig. 6). FIG. 4 Main exposures for neck-shoulder and low-back pain among computer and smartphone users. Pain in users of visual display units Chapter | 27 UNCORRECTED PROOF 6The Neuroscience of Pain FIG. 5 Examples of ergonomic and exercise interventions aiming at reducing the occurrence of musculoskeletal pain in white-collar employees. FIG. 6 Effects of exercise therapy for work-related musculoskeletal pain. Neck-shoulder strength exercise programs and general fitness training are effective to manage work-related NSP and disability among white-collar workers, with high-quality evidence for endurance and stretching exercises to help workers “at risk”(Chen et al., 2018). Most protocols include two to three sessions of 20 min. Weekly up to 52 weeks and show a strong association between treatment adherence and NSP relief (Chen et al., 2018). Five weeks of strength training induce neuromuscular changes facilitating the H-reflex excitability and increase strength and rate of force development of the trapezius muscle (Vangsgaard, Taylor, Hansen, & Madeleine, 2014). Central adaptations of pain responses, as a result of exercise-induced hypoalgesia, are also observed following eccentric training in computer users with NSP (Heredia-Rizo et al., 2019;Heredia-Rizo, Petersen, Arendt-Nielsen, & Madeleine, 2020). However, there are contradictory findings as to which exercises are the most effective and about the importance of supervision when training at the workplace. Variability is important to prevent MSDs (Madeleine, 2010). Taking active breaks from computer work has been studied to check if active pauses, compared to passive pauses, can change the activation pattern of the shoulder girdle muscles (St-Onge, Samani, & Madeleine, 2017). Active pauses induce a dynamic reorganization of muscle activity that could be beneficial since it changes muscle activation pattern (Samani, Holtermann, Søgaard, & Madeleine, 2009). That approach can be integrated using online biofeedback during computer work as a mean to increase variability in muscle activation (Samani, Holtermann, Søgaard, & Madeleine, 2010). For LBP, there is high-quality evidence to support exercise therapy (Maher, Underwood, & Buchbinder, 2017), both at home and at the workplace (del Pozo-Cruz et al., 2012). In users of VDUs, a spinal stabilization protocol (Kim, Kim, & Cho, 2015) or the combination of strengthening, mobility, and stretching exercises (del Pozo-Cruz et al., 2012) helps to decrease pain and disability, and improve proprioception, range of movement, and quality of life, with conflicting findings (Suni, Rinne, Tokola, Mänttäri, & Vasankari, 2017). Additionally, exercise training can reduce LBP recurrence (del Pozo-Cruz et al., 2012) and prevent pain in workers with reduced trunk muscle endurance and ex UNCORRECTED PROOF Chapter | 27 7 tension flexibility (Sihawong, Janwantanakul, & Jiamjarasrangsi, 2014). In general, 5–10 min of daily training could be enough to improve LBP-related measures (del Pozo-Cruz et al., 2012), with shorter sessions recommended for those who work long shifts (Bell & Burnett, 2009). Adherence is one of the main barriers in the real-life scenario. Several strategies are suggested to enhance compliance, such as flexible enrollment and engagement options, constant therapist-worker communication, and a tailored individual approach (Mullane et al., 2019). Ergonomics to prevent occupational musculoskeletal pain in computer and smartphone users Ergonomic interventions to adapt the job environment and the working process have been investigated. The issue of prolonged sitting has attracted special attention, and standing at work is promoted as a potential positive approach to improve musculoskeletal health. Along with this, computer and smartphone users should be well educated about proper ergonomics and sit-stand workstations (Agarwal, Steinmaus, & Harris-Adamson, 2018). With no consensus on an “optimal”sitting position, transitioning from a seated to a standing posture appears to be beneficial to prevent and treat MSDs and shows no negative impact on productivity (Waongenngarm, Areerak, & Janwantanakul, 2018). Interestingly, sustained standing may be detrimental for LBP, as previously explained, thus workers need to be individually trained to progressively include workstation adjustments. A systematic review concluded that there is very low- to moderate-quality evidence for the role of physical, i.e., arm support or mouse based on neutral posture, and organizational ergonomic interventions, i.e., change of work-rest cycle, to manage occupational NSP (Hoe et al., 2018). Still, adapting the working environment is especially effective in symptomatic workers (Chen et al., 2018). All in all, more up-to-date studies are needed, as workstations have evolved from a stationary to a mobile design, including the use of tablets and smartphones for office work, and work in various environment (office and home workplaces). Low levels of compliance with these interventions represent an important concern and may explain the contradictory results among studies. Therefore, strategies to improve compliance are needed. Applications to other areas We have reviewed how occupational MSDs impact the health condition of computer and smartphone users. A complex interaction of individual, and personal or job-related physical or psychosocial risk factors explain the high heterogeneity of cases. A society that is becoming more sedentary and a stressful working environment represent a dangerous cocktail in a highly competitive context. This reality is not exclusive of white-collar workers, but also applies to students and blue-collar employees. Among the modifiable risk factors, poor working postures, job strain, and the individual physical capacity need to be targeted when dealing with occupational musculoskeletal pain. The goal of health promotion at work is to decrease health risks and actively prevent disease incidence. Lack of physical activity represents a serious health burden beyond the working setting. It is associated with increased morbidity and mortality, and a risk factor for many severe conditions, i.e., cardiovascular diseases, diabetes, and dementia, among others. Regular physical activity helps to modulate the immune and pain inhibitory systems and promotes psychological well-being. Interventions that promote physical activity are safe and cost effective to reduce pain and disability, improve the quality of life, and enhance social participation. Not to forget, exercise training needs to be individually tailored to increase compliance. Despite all this, exercise programs are rarely a first-line treatment option. This applies to many other chronic pain conditions. A major issue is to close the gap between scientific evidence and clinical practice. Health professionals are to lead a transition from a traditional passive model to a more active and individual-based approach, where patients represent the cornerstone of the intervention. Other agents of interest We have described in detail the origin, mechanisms, and adaptations associated with NSP and LBP, as well as the strategies used to prevent and manage MSDs in users of VDUs. Other possible, but less frequent, repetitive strain injuries may include the elbow, wrist, forearm, and hand. Additionally, computer-related visual symptoms are becoming more common in white-collar workers. Smartphones and tablets represent a major communication tool nowadays, both in adults and among children and adolescents. Despite the clear advantages of the modern technology in many different fields, i.e., health, education, and work, Pain in users of visual display units Chapter | 27 UNCORRECTED PROOF 8The Neuroscience of Pain there is increasing interest about the health and safety issues associated with the inappropriate use of these devices. In fact, excessive computer and smartphone use has been linked with increased prevalence of tension type headache and migraine, and is reported to have a negative impact on the psychological, cognitive, and social domains. For instance, problems such as a disorganized life, poor concentration and performance at school or work, reduced sleep quality, and difficulties in written and verbal communication have been observed in those who overuse smartphones. Even the possible harm of the electromagnetic radiations of these devices has been the focus of previous research. Education for the responsible use of smartphones, tablets, and computers is mandatory and should be stressed in today’s society. Keeping an active physical and social life directly benefit mental health and well-being and should be balanced with a rational use of VDUs. Mini-dictionary of terms Ergonomics: Applied science promoting safe and efficient interactions between the employee and the physical, organizational and cognitive aspects of the working environment. Exercise intervention:Planned intervention including structured and repetitive movements to maintain or improve physical fitness. Occupational risk factor: A physical, psychosocial, or any other agent that may cause harm to an exposed worker in the job setting. Visual display unit: An electronic device displaying text and images in a screen. Work-related musculoskeletal disorder: Any condition provoked or worsen by performing a certain job or linked to the working context itself. Key facts Key facts of risk factors •Physical and psychosocial risk factors are of equal importance and need to be considered together. Key facts of interventions in computer users •High-quality evidence supports the use of exercise programs in while-collar workers. •Work variability is important to prevent occupational MSDs. •Lack of compliance is a critical challenge. •Ergonomic interventions can be effective. Summary points •Occupational NSP and LBP is a health issue in computer and smartphone users. •Peripheral and centrally mediated mechanisms are involved in work-related musculoskeletal pain. •Age and sex/gender may play a role in NSP and LBP in office workers. •Current research has produced limited evidence for the association of workplace physical risk factors with NSP and LBP. •Psychosocial risk aspects have a strong additive effect combined with physical risk factors. •Exercise therapy is effective to manage work-related MSDs in computer and smartphone users. •Ergonomic interventions may help to improve pain, although further evidence is warranted. References Agarwal, S., Steinmaus, C., & Harris-Adamson, C. (2018). Sit-stand workstations and impact on low back discomfort: A systematic review and meta-analysis. Ergonomics, 61, 538–552. Akkarakittichoke, N., & Janwantanakul, P. (2017). Seat pressure distribution characteristics during 1 hour sitting in office workers with and without chronic low back pain. Safety and Health at Work, 8, 212–219. Andersen, L.L., Mortensen, O.S., Hansen, J.V., & Burr, H. (2011). A prospective cohort study on severe pain as a risk factor for long-term sickness absence in blue- and white-collar workers. Occupational and Environmental Medicine, 68, 590–592. Bell, J.A., & Burnett, A. (2009). Exercise for the primary, secondary and tertiary prevention of low back pain in the workplace: A systematic review. Journal of Occupational Rehabilitation, 19, 8–24. Bevan, S. (2015). Economic impact of musculoskeletal disorders (MSDs) on work in Europe. Best Practice and Research: Clinical