The purpose of this study was to report on the health benefits and curative effects of aquatic exercise.
We adopted the results of high-grade study designs (ie, randomized controlled trials and nonrandomized controlled trials), for which there were many studies on aquatic exercise. Aquatic exercise, in this study, means walking in all directions, stretching, and various exercises and conditioning performed with the feet grounded on the floor of a swimming pool. We excluded swimming. We decided to treat aquatic exercise, underwater exercise, hydrotherapy, and pool exercise as all having the same meaning.
Aquatic exercise had significant effects on pain relief and related outcome measurements for locomotor diseases.
Patients may become more active, and improve their quality of life, as a result of aquatic exercise.
In recent years, Japan has become a fast-aging population, with the greatest longevity in the world. According to statistics released by the Japanese Health, Labor, and Welfare Ministry, the proportion of Japanese aged 65 years and older reached 20.8% in 2006, and is estimated to reach 39.6% by 2050. Total national medical costs were about US$262 billion, while the national income of Japan was about US$3.05 trillion.1 The national medical cost in 2002 was 8.58% of national income and has been increasing each year. When the national medical cost is divided among those aged 65 years or older, and those younger than 65 years, the costs of the former amount to $US128 billion ($5428 per person per year), while the cost for the latter is US$133 billion ($1285 per person per year). This indicates that overall medical costs for the elderly are extremely high in Japan. According to records for April, 2004, the number of beneficiaries of public care insurance was about 3,140,000, at a cost of about $US46 billion. Since the current insurance care system may go bankrupt without revision, the establishment of a “prevention-oriented (care prevention) system” was suggested in the revised care insurance system that was implemented in April, 2006.
The prevalence of obesity and metabolic syndrome (MS) is increasing in many industrialized countries. This situation also exists in Japan. The prevalence of MS, diagnosed according to Japanese criteria, was 18.4% and 5.8% for men and women, respectively.2 Among the indicators of MS, high blood pressure was most frequently observed, followed by dyslipidemia. High fasting plasma glucose occurred least frequently in both sexes.
The health benefits of physical activity are well documented for middle-aged and elderly people. Increasing physical activity has been shown to be effective for the prevention of coronary heart disease, stroke, diabetes, obesity, and hypertension, and for the improvement of quality of life (QOL) and mental health.3–8
There are many studies on exercise, but there are few reports that summarize the results of evidence grading of water exercise. Therefore, this study reports on the health benefits and curative effects of aquatic exercise.
Aquatic exercise, in this study, means walking in all directions, stretching, and various exercises and conditioning, with the feet grounded on the floor of a swimming pool. Regardless of sex and age, swimming is not an exercise that many people can perform. We decided to treat aquatic exercise, underwater exercise, hydrotherapy, and pool exercise as having the same meaning. In all geographic areas, except the tropics, a warm-water swimming pool was used (approximately 30°C).
Concept of evidence grading for evaluating curative and health-enhancement effects9
The concept of evidence grading is used in evidence-based medicine and in evidence-based health policy. The concept is supported worldwide, in both epidemiological and clinical studies (Table 1). Grades considered most likely to provide convincing evidence are Grade I: “evidence (systematic review [SR]) obtained from meta-analyses of randomized controlled trials (RCTs);” and Grade II, defined as “evidence obtained from at least one RCT.” The lowest grade, indicating the least convincing evidence, is Grade VI: “evidence (without data) obtained from expert committee reports or opinions and/or clinical experience of respected authorities.” If a study receives two different grades, the upper rank is adopted. RCTs, in particular, have recently been gaining attention in epidemiological and clinical studies, because they are the most effective study design for controlling for differences among humans, and can successfully show the effects of certain interventions (eg, tai chi exercise). We adopted the results of high-grade study designs, of which there were many for studies on aquatic exercise.
SR of SRs of RCTs for aquatic exercise
A systematic review of SRs of RCTs reported that aquatic exercise had small but statistically significant effects on pain relief and related outcome measures for locomotor diseases (eg, arthritis, rheumatoid diseases, and lower back pain). However, the long-term effectiveness was unclear.10 Our study was based on a review of articles in databases from 1990 to August 17, 2008. We described the structured abstract of three SRs (Table 2). The SRs of aquatic exercise showed a curative effect in all studies. Aquatic exercise had a small but statistically significant effect on pain, function, QOL, and mental health, and included more voluntary movement during water immersion. However, it should be noted that this was only the immediate effect of intervention, and not the long-term result. The intervention periods ranged from 3 weeks to 12 months in aquatic exercise studies. This might reflect the difficulty of maintaining long-term participation in an RCT. Whatever the case, the long-term effects are not clear.
Overall, aquatic exercise had a small (but statistically significant) effect on pain relief and related outcome measurements for locomotor diseases.
SR of nonrandomized controlled trials (nRCTs)
A current SR of nRCTs reported that 21 trials met inclusion criteria.11 The study was based on a review of articles in databases from 2000 to July 20, 2009. Target diseases were knee and/or hip osteoarthritis,12–14 poliomyelitis,15 chronic kidney disease,16 discomforts of pregnancy,17 cardiovascular diseases,18 and rotator cuff tears.19 Many studies on nonspecific disease (healthy participants) were included.20–32 All studies reported significant effectiveness for one or more outcomes. In particular, many studies reported that aquatic exercise had a significant effect on pain relief and other outcome measurements for locomotor diseases.12–15,19 Intervention periods ranged from 2 weeks to 12 months.
Table 3 shows the future research agenda for aquatic exercise.11 In advanced nations, it appears that there is interest in studies about mental health, as well as MS. Researchers should use the respective checklists for research design and intervention methods, which should lead to improvement in the quality of the study and contribute to the accumulation of evidence. Suitable comparisons are necessary to explain why aquatic exercise is better than other types of dynamic exercise. Aquatic exercise needs a valuable resource (hot water pool), which cannot be overlooked with respect to study feasibility.
Mechanism of pain relief for locomotor diseases
The warmth and buoyancy of water may block nociception by acting on thermal receptors and mechanoreceptors, thus influencing spinal segmental mechanisms.33,34 In addition, warm water may enhance blood flow, which is thought to help in dissipating algogenic chemicals and facilitating muscle relaxation. The hydrostatic effect of water may relieve pain by reducing peripheral edema35 and by dampening sympathetic nervous system activity.36 We should regard a mechanism to relieve the pain of locomotor diseases as a complex of factors, not as one factor.
Effects and expectations that accompany pain relief
People with obesity and MS become inactive and tend to be reluctant to perform physical activity. Therefore, due to weight gain and/or inactivity, they develop locomotor diseases, which include knee and back pain. It is also known that weight increases exacerbate obesity and MS.
Figure 1 shows the effects and expectations from aquatic exercise. Pain, in particular, limits the activity of people. There are various exercises that do not cause worsening of symptoms (pain). For aquatic exercise, the complex effect is great. It is certain that aquatic exercise has the effect of pain relief in locomotor diseases, and, as a result, patients may become more active and improve their QOL. Recent reports have demonstrated that comprehensive health education, which includes a combination of lifestyle education and aquatic exercise, has positive effects for middle aged and elderly people.37,38
There were some limitations to this study, as described above. Some selection criteria were common to the source studies. However, bias remained, due to differences in eligibility for participation in each study. Publication bias was also a limitation.
Aquatic exercise has significant effects on pain relief and related outcome measurements for locomotor diseases. Patients may become more active and improve their QOL as a result of aquatic exercise.
This study was supported by a Grant In Aid for Scientific Research (Representative Researcher, Prof H Kamioka) from the Ministry of Education, Culture, Sports, Science and Technology, Japan, 2011. We would like to express our appreciation to Ms R Higashino and Ms M Makishi for their assistance in this study.