Low back pain (LBP) is a common and multifactorial disorder with a high prevalence of up to 84%.1 Low back pain has become a serious social and economic problem due to the high costs of healthcare spending.2 As a type of musculoskeletal disorder, LBP is the leading specific contributor to years lived with disability.3 Low back pain is defined as back pain between the lower ribs and above the gluteal folds, with or without leg pain.4 Among the LBP patients who did seek medical care, approximately one third of patients presented with persistent back pain of at least moderate intensity 1 yr after an acute LBP, and a fifth of them reported substantial limitations in activity.5 In addition to medical treatment, as one of musculoskeletal physiotherapies, exercise therapy has been a common method of conservative intervention for LBP.6,7 Exercise has been shown to reduce pain and disability in patients with LBP.8 However, the therapeutic effect of exercise therapy lacks sufficient evidence to be confirmed.
Aquatic exercises are exercises that are performed in the water. The Chartered Society of Physiotherapists defined aquatic exercises as a therapy program taking advantage of the properties of water, designed by a suitably qualified physiotherapist, to improve function, ideally in a suitable pool.9 Evidence for the effectiveness of aquatic exercise has been reported in patients with rheumatic disease, fibromyalgia, stroke, Parkinson disease, and so on.10–13 Furthermore, there have been reports that use of aquatic therapy can improve dynamic balance and gait speed in adults with neurological conditions.14 Aquatic exercise is beneficial for improving neuromuscular function of the patients with neurologic disorders due to the advantages of the physical characteristics of water, including natural buoyancy, hydrostatic pressure, thermodynamics, hydrodynamic forces, and viscosity.11 However, there was no sufficient evidence to recommend that aquatic exercise is potentially beneficial to patients with LBP, so a systematic review of the literature and a meta-analysis are essential to clarify the role of therapeutic aquatic exercise in the management of LBP.
The aim of this study was to systematically analyze all evidence available in the literature about effectiveness of the aquatic exercise. For this purpose, we performed a systematic literature review and meta-analysis of randomized controlled trials (RCTs).
This study conformed to all Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines and reported the required information accordingly (see Checklist, Supplemental Digital Content, http://links.lww.com/PHM/A456).
PubMed, the Cochrane Library, Embase, and Cumulative Index to Nursing and Allied Health were searched in November 2016 for studies using the following combination of terms: “low back pain,” “lumbago,” “lower back pain,”, “low back ache,” “low backache,” “recurrent low back pain,” “postural low back pain,” “mechanical low back pain,” “low back pain,” “posterior compartment,” in combination with “aquatic exercise,” “aquatic therapy,” and “hydrotherapy,” and only RCTs were included. Bibliographies of potentially eligible studies were also reviewed to identify the additional studies. Only complete original journal articles were included, whereas abstracts or presentations were excluded.
The reviewers (ZJS and HXZ) independently searched and assessed potentially relevant studies for final inclusion. Disagreements were resolved by discussing with the corresponding author (SQF). Studies were considered for inclusion if they met the following criteria: (1) the type of study design was a RCT; (2) participants were adults with back pain between the lower ribs and above the gluteal folds, with or without leg pain, and the participants were accepting therapeutic aquatic exercise; (3) the intervention was the aquatic exercise compared with the general exercise or no exercise; (4) studies were required to report at least one of the following outcome measures: visual analog scale (VAS), Short-Form 12 Health Survey (SF-12) or Short-Form 36 Health Survey (SF-36); (5) sufficient data for evaluating the efficacy of aquatic exercise must be provided, and there were at least two measurements, before and after the exercise; (6) the article was published in English. Aquatic therapy means any exercises in water, including stretching, strengthening, range of motion, and aerobic exercise. Studies were considered for exclusion if they met the following criteria: (1) participants took pain medication while aquatic exercise; (2) LBP caused by pregnancy; and (3) non-RCTs or studies published as the following article type: abstracts, review articles, and letters.
Study quality and extracted data were assessed from the selected full-text articles by two investigators. The information of included articles (name of first author, publication year), the number and characteristics of participants (age, sex, disease duration), and intervention (duration, frequency, types of exercises) were extracted from each included article. Furthermore, all values (mean and SD) of the outcomes for low back pain of the aquatic exercises group, general exercise or control group, before and after the exercise period, were extracted. The primary outcomes analyzed were pain and quality of life. Pain was assessed by using VAS. Quality of life was assessed by SF-12 or SF-36 that allowed the calculation of physical component score and mental component scores.
Data were analyzed using Review Manager Software (RevMan Version 5.2; The Nordic Cochrane Center, The Cochrane Collaboration, Copenhagen, Denmark). The meta-analysis was performed using the random effects model. The results were expressed in terms of odds ratio and a 95% confidence interval (CI) for dichotomous outcomes and in terms of standardized mean difference (SMD) and 95% CI for continuous outcomes. We used Cochran's Q statistic, I2 statistic (I2 > 50% was used as a threshold indicating significant heterogeneity) to assess the heterogeneity.15 If the I2 value of more than 50%, and sensitivity analysis was performed to evaluate the influence of single study on the overall estimate and explore the heterogeneity.16 The risk of bias of included studies was assessed using the Cochrane risk of bias tool.
Our initial database search yielded 47 potential articles. After removal of duplicates and non-English articles, we screened the titles and abstracts, and 14 of them were retrieved for detailed analysis. After complete reading, eight articles met the inclusion criteria and were finally identified to evaluate the effect of aquatic exercise on LBP. Figure 1 shows the process of study selection.
A total of 331 patients were randomly assigned in the eight trials included in this meta-analysis. Regarding sex, 38.1% (n = 126) of patients were men and 61.9% (n = 205) were women. The overall mean (SD) age was 44.34 (13.88) yrs. The more detailed characteristics of the included studies are listed in Table 1.
In the eight trials, the experimental group received aquatic exercise, multimodal physical therapy program, or standard general practice, whereas the comparison group received land-based therapy, standard general practice, or no exercise. Aquatic exercise program consisted of warming up, jumping, jogging, fast running, active range of motion of the joints, stretching, strengthening, and relaxation in the water.17–24 Land-based exercise program consisted of warming up, basic flexion, extension, mobilization, stretching, strengthening major muscle groups, relaxation, and aerobic exercise.18,21,23,24 Standard general practice consisted of a physician's consultation and educational booklet only.20 The duration of aquatic exercises programs ranged from 4 to 15 wks.17–24 The duration of sessions varied from 30 to 80 mins.17–24 The frequency of sessions ranged from two to five times per week.17–24Table 2 lists the details of intervention.
Quality of Trials
The quality assessment of the included trials has been performed by two researchers independently according to the Cochrane risk of bias tool, and the results of the assessment can be observed in Figure 2 (the red with a minus means high risk of bias; the yellow with a question mark means unclear; the green with a plus means low risk of bias). Seven RCTs have low risk of random sequence generation, and one has high risk.17 The trial at high risk of random sequence generation did not randomize the patients for practical and ethical reasons. All the RCTs are at low risk for allocation concealment. One trial is at high risk of blinding of outcome assessment,20 whereas other trials are at low risk or unclear. The trial at high risk of blinding of outcome assessment was a single-blind RCT, and the physiotherapist were aware of the patient assignment. Other bias (such as recruitment bias and contamination of the interventions) occurs for issues not elsewhere covered. The rate of patients lost to follow-up was lower than 20%.
Reduction in pain is the primary indicator for evaluating the treatment result in patients with low back pain. All the trials assessed the pain intensity by using VAS. Because of the different range and scoring methods of VAS in these trials, SMD was used. According to the results of meta-analysis, patients who were treated with aquatic therapy showed a statistically significant reduction in pain intensity compared with patients in the control group (SMD = −0.65, 95% CI = −1.16 to −0.14; I2 of heterogeneity 78%; random effects model) (Fig. 3). Because of I2 value of 78%, we further performed a sensitivity analysis by omission of each study to evaluate stability of the results. The result showed that one trial significantly affected the heterogeneity, and the heterogeneity could lower from 78% to 43% when removing the trial of Baena-Beato et al.17 in 2014 (SMD = −0.40, 95% CI = −0.73 to −0.07; I2 of heterogeneity 43%; random effects model) (Table 3). The sensitivity analysis suggested that the combined SMDs were stable after any of the studies was excluded from the current meta-analysis. Therefore, a positive correlation between aquatic therapy and relief of pain existed after any study was excluded from the current meta-analysis.
Quality of Life
In the eight trials, two of these studies used the SF-36 to assess the quality of life,17,21 and two used the SF-12.20,22 All of the four studies assessed the physical component and mental component to measure treatment result in patients with LBP. The meta-analyses result of physical component showed a statistically significant improvement in the experimental group compared with the control group (SMD = 0.63, 95% CI = 0.17 to 1.09; I2 of heterogeneity 61%; random effects model) (Fig. 4). Because of I2 value of 61%, we further performed a sensitivity analysis by omission of each study to evaluate stability of the results. The result showed that one trial significantly affected the heterogeneity, and the heterogeneity could lower from 61% to 0% when removing the trial of Cuesta-Vargas et al.20 in 2012 (SMD = 0.43, 95% CI = 0.11 to 0.75; I2 of heterogeneity 0%; random effects model) (Table 4). The sensitivity analysis indicated that the combined SMDs were stable after any of the studies was excluded from the current meta-analysis. Therefore, a positive correlation between aquatic therapy and improvement of physical condition existed after any study was excluded from the current meta-analysis. Furthermore, a nonsignificant difference in mental component was found in the experimental group compared with the control group (SMD = 0.46, 95% CI = −0.22 to 1.15; I2 of heterogeneity 82%; random effects model) (Fig. 5).
In this meta-analysis, which included 331 patients with LBP from eight RCTs, we summarized the eight studies in efficacy of aquatic exercise, and the analysis revealed that aquatic exercise could statistically significantly reduce pain and increase physical function in patients with LBP. There was no significant effectiveness with regard to general mental health in aquatic group.
The overall SMD in pain intensity was −0.65. However, the statistically significant reduction of VAS score is not uniform along clinically significant changes in pain.25 In a previous study, using a 100-mm VAS, the mean VAS change in all patients reporting a “little less” or a “little more” pain was 13 mm.26 The minimal clinically important difference (MCID) of the VAS for LBP has been reported in range from 20 to 35 mm.27 Furthermore, there was another study suggesting that pain reductions of at least 33% are considered clinically relevant.28 However, another study showed inconsistent suggestion that a 20% reduction in the pain score is considered to be clinically relevant.19,29 Therefore, the MCID for pain is usually different in different patient population, and the criterion standard for clinically significant changes in pain remains controversial. In current study, a statistically significant reduction in pain intensity (SMD = −0.65, 95% CI = −1.16 to −0.14) does not necessarily mean a clinically significant change in pain, so these results should be interpreted with caution. Therefore, we recommend that further studies should closely combine the VAS score with description of the clinical condition of the patients, and the clinically significant relief of pain is considered as the main goal of treatment.
The SF-36 and SF-12 are simple and inexpensive measures of health outcomes, and they are continuous scales to detect the changes in health.30 The exact value of the MCID is not a fixed value, and the published MCID values of physical function for LBP range from 7 to 16 points (SF-36).31,32 However, the MCID value of SF-12 physical function for LBP is unclear. According to the results of our analysis, we observed a statistically significant increase in physical function in the experimental group, and these results should be interpreted with caution because they do not necessarily mean a clinically significant change in physical function. Furthermore, we did not observe an improvement in the general mental health, and this may be related to the lack of effect of intervention on psychosocial aspects in the four included trials.
Aquatic exercises are frequently used as a treatment for the rehabilitation of patients with musculoskeletal disorders.33 Previous researches have demonstrated that the hydrostatic effect of aquatic exercise can facilitate the relief of pain via reducing peripheral edema and inhibition of sympathetic nervous system activity.34 In a previous systematic review, therapeutic aquatic exercise has shown to be safe and effective in the patients experiencing chronic low back pain.35 Furthermore, the result of a meta-analysis of spa therapy and balneotherapy showed that spa therapy and balneotherapy may be effective for treating patients with LBP; however, spa therapy and balneotherapy were nonactive.36 In the current study, the trials that concerned the active aquatic exercise for LBP were included, and the results provided reliable evidence that aquatic exercise was beneficial for reducing pain and disability and had the potential to be a part of exercise program for patients with LBP.
Low back pain has a significant impact on functional capacity because the pain can restrict occupational activities.37 Our meta-analysis showed that aquatic exercise statistically significantly decreased the VAS scores and increased physical function, and these result suggested that aquatic exercise played a positive role in improving in pain and physical health-related quality of life. Consequently, the results of this meta-analysis can provide reliable evidence for evaluating the interventional effectiveness of aquatic exercise. In respect to the limitations of this study, the total number of patients involved in the meta-analysis was so small that we could not identify relatively small disparities between experimental group and control group. Moreover, in this meta-analysis, the results showed significant heterogeneity when we used the random-effect models, and we performed sensitivity analysis to explore the heterogeneity and found the trials significantly affecting the heterogeneity. The heterogeneity was likely due to the different kinds of exercise programs, including the type of exercise, the frequency of sessions, the number of sessions, and the duration of sessions. Moreover, the different durations of LBP may have affected the heterogeneity. It is possible that we missed some published or unpublished articles that concerned the therapeutic aquatic exercise. Furthermore, the results of the meta-analysis should be interpreted with caution because of the variability in study quality and potential conflicts of interest of the trials.
The analysis result revealed that aquatic exercise could statistically significantly reduce pain and increase physical function in patients with LBP. Aquatic exercises can be encouraged as part of exercise program for patients with LBP. However, given the limitations in our study, further investigation on a larger scale should be conducted to verify our findings.
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