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Impact of water therapy on pain management in patients with fibromyalgia: current perspectives

Authors Zamunér AR, Andrade CP, Arca EA, Avila MA

Received 15 August 2018

Accepted for publication 20 May 2019

Published 3 July 2019 Volume 2019:12 Pages 1971—2007

DOI https://doi.org/10.2147/JPR.S161494

Checked for plagiarism Yes

Review by Single anonymous peer review

Peer reviewer comments 5

Editor who approved publication: Dr Erica Wegrzyn

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Antonio Roberto Zamunér,1 Carolina Pieroni Andrade,2 Eduardo Aguilar Arca,3 Mariana Arias Avila4

1Departamento de Kinesiología, Universidad Católica del Maule, Talca, Maule, Chile; 2Secretaria de Saúde do Município de Guareí, Guareí, São Paulo, Brasil; 3Departamento de Fisioterapia, Universidade do Sagrado Coração, Bauru, São Paulo, Brasil; 4Departamento de Fisioterapia e Programa de Pós-Graduação em Fisioterapia, Universidade Federal de São Carlos, São Carlos, São Paulo, Brasil

Abstract: Exercise-related interventions have been recommended as one of the main components in the management of fibromyalgia syndrome (FMS). Water therapy, which combines water’s physical properties and exercise benefits, has proven effective in improving the clinical symptoms of FMS, especially pain, considered the hallmark of this syndrome. However, to our knowledge, the mechanisms underlying water therapy effects on pain are still scarcely explored in the literature. Therefore, this narrative review aimed to present the current perspectives on water therapy and the physiological basis for the mechanisms supporting its use for pain management in patients with FMS. Furthermore, the effects of water therapy on the musculoskeletal, neuromuscular, cardiovascular, respiratory, and neuroendocrine systems and inflammation are also addressed. Taking into account the aspects reviewed herein, water therapy is recommended as a nonpharmacologic therapeutic approach in the management of FMS patients, improving pain, fatigue, and quality of life. Future studies should focus on clarifying whether mechanisms and long-lasting effects are superior to other types of nonpharmacological interventions, as well as the economic and societal impacts that this intervention may present.

Keywords: hydrotherapy, exercise, pain management, chronic pain, physical therapy, aquatic therapy

Introduction

Fibromyalgia syndrome (FMS) is a chronic syndrome characterized by widespread musculoskeletal pain, chronic fatigue, and nonrestorative sleep, among other symptoms.1,2 It can be considered a clinical and pathological heterogeneous syndrome, thus requiring individualized and patient-tailored treatment.3 FMS is one of the most common conditions seen in the general population and outpatient rheumatology practice.1

The burden of FMS is substantial and comparable to some other chronic disease such as osteoarthritis, rheumatoid arthritis, diabetes, and hypertension.46 FMS patients incur direct costs approximately equal to rheumatoid arthritis patients, but visit more emergency physicians, physicians, and physical therapists than rheumatoid arthritis patients.7 Several studies have evaluated the economic burden of FMS, including direct and indirect costs of the disease.6,815 These costs include the large number of medical consultations and medication, and the health system and societal expenses of disability from work, accounting for more than three-quarters of total FMS-related costs.16 Hence, a cost-effective treatment, or at least one that helps decrease the economic and societal burden, is more than welcome.17

Recent recommendations for the management of FMS have suggested the use of pharmacological and nonpharmacological interventions,18 with exercise being recognized as one of the most important components of FMS treatment.1922 Moreover, aerobic and strengthening exercises were the only therapeutic approach with a “strong for” recommendation by the European League Against Rheumatism,18 due to its positive effects on pain, physical function, and well-being, along with its availability, relatively low cost, and low risk.2326

Among different types and modalities of exercises for FMS, water therapy can be considered one of the most known and doctor-recommended interventions, as it combines water physical properties and exercise benefits.22,27 Indeed, several studies have investigated the effects of water therapy as a strategy in the management of FMS, reporting improvements in well-being, fitness, and symptoms, especially pain.2832 However, to our knowledge, mechanisms underlying the water therapy effects on pain are still scarce. Therefore, the aim of this narrative review is to present the current perspectives of water therapy and the physiological basis for the mechanisms supporting its use for pain management in patients with FMS.

Clinical implication of water physics

Aquatic exercise describes an environment for structured activity rather than a type of exercise, as water's physical properties and the physiological effects of immersion turn this environment into a unique one.33 According to the Chartered Society of Physiotherapists, water therapy or aquatic exercise refers to the use of water properties to design a therapy program aimed at improving function.27,34 Indeed, there is evidence27 that aquatic exercise is able to reduce the burden of musculoskeletal illnesses, which rely, basically, on the therapeutic effects achieved by the summation of physiological effects of immersion and principles of hydrodynamic exercises.35 The four most important water physics principles are buoyancy, resistance (drag forces), hydrostatic pressure, and thermal conduction. Definitions of the water physics principles, their properties, and implications for clinical use are summarized in Table 1.27,27,31,3547

Table 1 Summary of water physics principles

Water therapy physiological effects and its relationship with pain

Several studies have reported beneficial effects of aquatic therapy on several conditions,33,39,4850 among which stands FMS.27,28,32,51,52 Indeed, guidelines for the management of FMS18 have recommended water therapy mainly due to its analgesic effects and improvement in quality of life.27,28,32,51,52

Although this narrative review does not intend to perform a systematic review on the theme, Table 2 summarizes the clinical trials assessing the effects of hydrotherapy on FMS symptoms, especially pain. We carried out a search of the following databases: MEDLINE/PubMed, Scopus, Web of Science, SciELO, CINAHL, LILACS, ScienceDirect, and Springer. The following keywords were used: “aquatic exercise”, “aquatic training”, “balneotherapy”, “fibromyalgia”, “fibromyalgia syndrome”, “fibromyalgic patients”, “hydrotherapy”, and “pool-based exercises”. Two authors independently extracted data from all of the trials and all discrepancies or disagreements were resolved by consensus.

Table 2 Summary of studies using water therapy for FMS treatment

Randomized clinical trials, nonrandomized clinical trials, and crossover design studies assessing the effects of any aquatic intervention on pain in FMS patients were considered eligible for inclusion. The methodological quality of the studies was analyzed using the PEDro scale.

Thirty-five studies were included. Methodological quality varied between 1 and 9 according to the PEDro scale. Water temperature ranged between 28 and 37/38 ºC, and 7 studies did not report. Regarding the effectiveness of water therapy, only 2 studies reported no significant improvement compared to the baseline condition. However, one of these studies was composed of only 10 participants (5 in the Ai Chi group and 5 in a control group; PEDro score=1)83 and the other comprised 18 participants (9 in the sauna group and 9 in the hydrotherapy group; PEDro score=4).84 Thus, 94% of the included studies showed improvement in pain besides ameliorating other symptoms. In the following sections, we will discuss the possible mechanisms underlying the aquatic exercise effects.11,28,30,31,8382

Musculoskeletal and neuromuscular systems and the association with pain

The main symptom reported by FMS patients is pain.1,2,85,86 Pain is a dynamic and complex phenomenon that is the final result of several factors. The association between nociceptive activity and pain perception depends on several intrinsic and extrinsic influences. For the same nociceptive stimulus, pain perception and related brain activity will greatly differ between subjects. In the case of chronic rheumatic diseases that do not regress spontaneously, such as FMS, functional and structural central nervous system changes cause a generalized reduction in the pain threshold that is not limited to the anatomical structures involved, thus leading to the hyperalgesia and allodynia in many, if not all, body regions.21 FMS is associated with changes in the central nervous system that affect sensory information processing, amplifying peripheral input and/or generating pain perception in the absence of a noxious stimulus.21 People with FMS are reported to present hyperactivity of the hypothalamic–pituitary–adrenal axis,86,87 and this may be linked to the initiation or worsening of FMS symptoms. Moreover, dopamine dysfunctions have been linked to the pathophysiology of FMS, which are associated with hyperalgesia and deficient pain inhibition.59

Accordingly, exercise has been one of the most recommended nonpharmacological interventions for FMS.19,20 It has been shown that exercise is able to influence gene expression and structural complexity in the limbic structures that regulate the hypothalamic–pituitary–adrenal axis21 and can improve conditioned pain modulation due to increased endogenous opioids, stimulation of brain structures involved in the inhibitory descending pathways that regulate painful response.88 Geytenbeek89 has examined over 500 articles that were available on the theme and has concluded, after examining randomized controlled trials, case–control studies, and cohort studies, that high to moderate quality evidence supports the use of hydrotherapy for pain, function, joint mobility strength, and balance. Moreover, exercise seems to be the most effective component of a hydrotherapy program for FMS.89,90

Hence, exercising in an aquatic environment is advantageous. The pain-relieving effect of water-based exercises is suggested to be due to the joint effect of exercise, warm water, and buoyancy on thermal receptors and mechanoreceptors.33 Sensory-motor hyperstimulation exerted by the hydrostatic pressure, viscosity, and water temperature increases the triggers of thermal receptors and mechanoreceptors while blocking nociceptors.48,91 The viscosity of the water provides an environment with three-dimensional resistance, which facilitates proprioceptive feedback through functional patterns of movement and increases the synchronization of the motor units due to slowed movement.92 Also, immersion in warm water helps to increase blood flow and oxygen supply, improving nutrition and removal of catabolites, and thereby reducing signal molecules, such as IL-8 and noradrenaline,58 responsible for activation of nociceptors.93 In addition, regular exercise has been shown to improve overall health, as shown in other chronic conditions.27 This prominent effect on pain could be previously observed in several studies.27,28,31,32,53

It is noteworthy to mention that patients with FMS present abnormalities regarding pain modulation, including central sensitization and other pathophysiological mechanisms, such as the accumulation of cytotoxic substances in the extracellular space (glutamate, lactate, bradykinin, prostaglandins, etc.) generated by muscle activity, which exert algogenic effects by sensitizing and exciting nociceptors.94,95 Glutamate is a major cortical excitatory neurotransmitter that acts in pain neurotransmission. Increased levels of insular glutamate have been reported to be present in FMS. In addition, the concentration of this molecule is correlated with pain report. Enhanced glutamatergic neurotransmission resulting from higher concentrations of glutamate within the posterior insula may play a role in the pathophysiology of FMS and other central pain augmentation syndromes.96 Moreover, the sympathetic nervous system, which is already in a condition of hyperactivity (see section “Cardiovascular and respiratory systems and the association with pain”), under the action of bradykinin stimulates the release of noradrenaline and prostaglandins that further potentiate sympathetic hyperactivity and sensitize the nociceptors.

Therefore, another mechanism explaining the pain improvement may rely on the combination of hydrostatic pressure and temperature on nerve endings, which would lead to competing stimuli that would diminish the peripheral nociceptive input.97 Aquatic therapy also leads to muscle relaxation,98 which would in turn lead to less pain. Buoyancy decreases compressive weight-bearing stresses on joints and allows functional exercise with lessened gravitational load, making the movements easier, and even facilitating the improvement of both strength and range of motion.39,99 Furthermore, drag forces can be used as a resource to assist movements or to impose resistance favoring muscle strengthening.33 Nonetheless, quantifying the resistance training intensity and planning a progressive overload program in aquatic environments is challenging due to several factors (eg, speed of movements, range of motion, shape and size of floats, etc.). Therefore, it is still not clear whether aquatic exercises can really induce strength gains, since controversial results have been reported.33

Regarding chronic fatigue, another core feature of FMS, its perception may be reduced after water therapy due to the buoyancy effects.40 Buoyancy helps reduce the musculoskeletal system’s gravitational forces due to gravitational muscle relaxation and energy conservation, which seems to reduce perceived fatigue. Water immersion may also reduce neuromuscular responses or trigger inhibitory mechanisms, with an overall reduction in neural transmissions, which would impact not only on the perceived fatigue but also on the nociceptive input, reducing pain perception.

Cardiovascular and respiratory systems and the association with pain

FMS patients present cardiorespiratory dysfunction characterized by reduced respiratory muscle endurance, inspiratory muscle strength, and thoracic mobility.100 Moreover, cardiovascular autonomic control and baroreflex sensitivity have been also shown to be altered in this population.32,101,102 In addition, although it is not possible to identify a causal relationship, several studies have shown that these cardiorespiratory abnormalities are related to the pain in these subjects. Forti et al100 showed that inspiratory muscle strength is associated with the number of active tender points. In addition, Zamunér et al103 found that FMS show reduced respiratory sinus arrhythmia magnitude as compared to healthy women. Also, the indices obtained during the deep breathing test, a vagal maneuver, had an important association with pain in FMS. In another study, Zamunér et al104 also showed that sympathetic activity, as assessed by muscle sympathetic nerve activity, was related to pain in this population.

Several studies have described the interaction between autonomic and nociceptive pathways occurring at multiple levels,105107 with the nucleus tractus solitarius playing an important role. The nucleus tractus solitarius, located in the brainstem, receives visceral information through the primary afferents of the vagus nerve and receives the spinal pathways involved in pain processing, functioning as an interface between the autonomic and sensory systems.107,108 Therefore, improving cardiovascular and respiratory outcomes in FMS patients should be considered one of the aims in the management of FMS.

It is well established that aerobic exercise improves cardiorespiratory function in patients with FMS.19,109 In addition, an aquatic environment can allow higher-intensity exercises to be undertaken, with lower cardiovascular stress than is possible on land.19,110 In this sense, some studies have assessed the effects of water therapy on the cardiorespiratory system. Zamunér et al32 found that a 16-week aquatic therapy program proved to be effective in ameliorating symptoms, aerobic functional capacity, and cardiac autonomic control in FMS patients. Surprisingly, improvements in cardiac autonomic control were related to the improvements in pain and the impact of FMS on quality of life, thus suggesting an important role of autonomic control mediating symptoms. Regarding the improvement of functional aerobic capacity, aquatic therapy has also been proven to be effective.32,51,80 However, studies have shown no association between cardiorespiratory fitness improvements and FMS symptom improvements.32,51,111113

In summary, cardiorespiratory function and cardiac autonomic control should be routinely monitored in the management of FMS patients since they seem to be related to the symptoms; and water therapy might be seen as a strategic method to improve these outcomes in this population. However, improving cardiorespiratory fitness should not be the main goal in the therapy, but instead a tailored approach directed to the key FMS symptoms (pain, sleep disorders, fatigue, depression, disability) with exercise assignment that does not exacerbate post-exercise pain should take place.114,115

Neuroendocrine system and inflammation

Growing interest has been shown in the study of the benefits of aquatic therapy on the neuroendocrine system116118 and inflammation. However, little is known about these in FMS patients. This is of interest since neurohormonal abnormalities have been reported in this population, such as low levels of serotonin,119 hypothalamic–pituitary–adrenal axis dysfunction,120122 and low levels of growth hormone, which is associated with poor sleep quality.123,124 Moreover, although there are no specific biomarkers for FMS, some studies have suggested the involvement of inflammatory disorders on its etiology.125,126 Those disorders involve cytokines, proteins responsible for mediating the inflammatory reaction in the immune system.127 Studies have shown that FMS patients have increased levels of serum IL-8,128 IL-6, IL-10, and IL-1β.129 Ortega et al130 found that FMS patients present a higher circulation concentration of C-reactive protein and that their monocytes release more IL-1β, tumor necrosis factor alpha, IL-6, and IL-10 than those from an age-matched healthy control group. Additionally, FMS patients present a greater concentration of IL-8 in cerebrovascular fluid.131,132 IL-8 release is stimulated by substance P secretion and promotes sympathetic pain,133 and thus is considered an inflammatory marker of FMS,62 which is indicative of underlying low-grade systemic inflammation. There is evidence showing the participation of chemokines (signaling molecules present in inflammatory and immune responses) in FMS, with higher concentrations of inflammatory chemokines (TARC/CCL17, MIG/CXCL9, MDC/CCL22, I-TAC/CXCL11, and eotaxin/CCL11).134

Aquatic therapy has been shown to reduce plasma levels of norepinephrine,135137 epinephrine,135,138 β-endorphin, and cortisol139 in healthy men. In this context, we may suggest that aquatic therapy may contribute to a reduction of stress, improvement of sleep quality, and reduction of pain sensitivity.26,137 Regarding FMS patients, to our knowledge, no studies have assessed the effects of aquatic therapy on the neuroendocrine system. However, Bote et al140 found that a single session of moderate cycling improved the inflammatory and stress status of FMS patients. Moreover, their results also suggest that the neuroendocrine mechanism seems to be an exercise-induced decrease in the stress response of these patients, since they observed a reduction in the systemic concentration of cortisol, noradrenaline, and extracellular heatshock protein 72. In agreement with these findings, Ortega et al130 studied the effects of an aquatic fitness program performed for 8 months twice a week. After the program, monocytes from FMS patients presented similar spontaneous release of IL-1β and IL-6 to that of healthy controls and a reduction in C-reactive protein, showing that aquatic exercise might exert anti-inflammatory effects.

Current perspectives

A considerable amount of evidence27 has shown that water therapy improves pain, fatigue, and quality of life. However, current recommendations for the management of fibromyalgia elaborated by the European League Against Rheumatism18 suggest a “weak for” recommendation, implying that most therapists would, although a substantial minority would not, recommend water therapy for FMS patients. This recommendation underlies the small amount of evidence suggesting superiority of water therapy over land-based therapies.141

Therefore, future studies should focus on the possible mechanisms explaining the beneficial effects of water therapy in order to elucidate whether they are similar or not to the mechanisms leading to the improvement of symptoms and quality of life promoted by land-based exercises. Moreover, studies should also compare the detraining effects or long-lasting effects promoted by water therapy and land-based exercises since these have been addressed only by a few studies and the results are controversial. A recent study54 showed that 16 weeks of aquatic exercise therapy was effective in improving aerobic capacity and symptomatology such as pain, quality of life, and fatigue in FMS patients. However, after 16 weeks of detraining, all variables returned to near baseline. Thus, elucidating whether this is comparable to land-based exercises would assist FMS patients and therapists on the proper therapeutic approach recommendation and selection.

Another noteworthy point to be mentioned regards the FMS patient’s adherence to treatment and engagement with aftercare tasks in the long term.86 Coupled with the fact that pharmacological interventions seem to be ineffective, as they seldom induce minimally important clinical differences in pain after 3 months of therapy,142,143 this makes the development of treatments that benefit patients over their lifetime extremely challenging. Hence, a multidisciplinary approach and educational strategies may be helpful additions to physical treatment, in this case, water therapy; these strategies show the importance of continuing with treatment, that the disease may vary in intensity over the time, and, more importantly, that they have to take responsibility for their healthcare and habits that influence on FMS symptoms, giving them tools to help with daily FMS management. Water therapy, in this context, comes as an alternative that makes movement easier and may increase compliance with the treatment.

Another topic to be discussed is the cost-effectiveness of water therapy for FMS. One previous study11 has shown that adding water therapy to the usual care for FMS patients is cost-effective for both healthcare and societal costs. The authors also concluded that the characteristics of facilities (distance from patients’ homes and the number of patients who can participate per session) are major determinants that have to be considered before a health manager decides to invest in such a program. Therefore, this point should be addressed in future studies that aim to elucidate whether the cost-effectiveness differs among other kinds of interventions. Studies involving cost-effectiveness may also be helpful in guiding the development of public policies for the healthcare of FMS patients, and, as such, are much needed.

The present study has some limitations, as it is not a systematic review. As such, performance of a metaanalysis was not possible. As a narrative review, the scope of the present study was to highlight and discuss the possible mechanisms involved in the improvement of pain for FMS patients who undergo water therapy. Nonetheless, this discussion is still difficult as the protocols described vary in duration, session length, and techniques used into the swimming pool, as well as the outcomes chosen; also, several outcomes are not sufficiently described.

Conclusion

Water therapy may be recommended as a nonpharmacologic therapeutic approach for the management of FMS patients, improving pain, fatigue, and quality of life; these therapeutic effects are achieved by the physiological changes caused by in-water exercising. However, future studies should be conducted in order to clarify the action mechanisms and whether long-lasting effects are superior to other types of intervention, especially land-based exercises.

Disclosure

The authors declare no conflicts of interest in this work.

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