Introduction
Stroke, a lack of blood supply to the brain, is the third leading cause of chronic disability in adults worldwide [
1,
2]. It was reported that there are 16.9 million patients with initial stroke, 33 million stroke survivors, 5.9 million stroke-related deaths, and 102 million Disability-Adjusted Life Years (DALYs) lost, with most of the burden in low-income and middle-income countries according to Global Burden of Disease (GBD) Study 2010 [
1]. Stroke survivors suffer varying functional disorder including balance dysfunction, walking disorder, cognitive impairment [
3]. Of all the functional disorders caused by stroke, balance impairment is the most common and considered to be primary impairment after stroke [
4‐
8]. Ambulatory impairment is another devastating sequelae as more than 30% of survivors remain unable to walk independently 6 months after a stroke [
3,
9‐
11]. Balance dysfunction and walking impairment make it difficult to complete activities of daily life (ADLs) safely, move at home or in the community, and live independently [
6,
7]. Meanwhile, balance impairment and walking dysfunction can result in lower confidence for movement and in completing ADLs, which may in turn further reduce activity [
12]. If not detected or left untreated, balance and walking impairment can lead to a cascade of serious, undesirable, and expensive events [
13,
14]. Balance and walking ability were also significant predictors of functional improvement after stroke [
15]. Thus, therapeutic intervention strategies need to pay close attention to improving balance and walking ability [
16].
Various rehabilitation programs have been developed to solve such problems as balance dysfunction, walking impairment, and limited ADLs related to stroke [
3]. These programs include Brunnstrom approaches, neurodevelopmental treatment (NDT), proprioceptive neuromuscular facilitation, and motor relearning programs [
17,
18]. Although these rehabilitation programs have been shown to be beneficial for stroke survivors, no superior specific approach or program has been discovered [
3], as other effective rehabilitation programs are being developed [
19]. However, only approximately 5 to 20% of post-stroke survivors achieve complete functional recovery after intensive rehabilitation efforts [
20,
21]. Therefore, there is an urgent need for new appropriate and promising rehabilitative program for inpatients and outpatients with stroke.
Hydrokinesitherapy, a promising intervention, combines the revitalizing and strengthening effects of the physical exercise with the muscle-relaxation and physical properties of water submersion [
22]. This technique was developed some decades ago when it was used as a rehabilitative approach for poliomyelitis [
23]. It was demonstrated that this treatment could be used as a rehabilitation program for patients with “weak muscles”. Later studies have shown that hydrokinesitherapy was beneficial for fitness and strength maintenance in various chronic conditions, including multiple sclerosis [
24,
25], Parkinson’s disease (PD) [
26], spinal cord injury [
23], cerebral palsy [
27], and arthritis [
28]. Hydrokinesitherapy has also been demonstrated to be suitable and safe for patients with stroke [
29]. Remarkably, recent studies suggested that hydrokinesitherapy has positive effects on posture balance control [
30], muscle strength [
31], fitness [
32], anxiety and depression scores [
33] and ADLs [
34] in patients with stroke.
Hydrokinesitherapy has positive benefits for stroke patients thanks to the essential physical properties of water such as its favorable specific gravity, buoyancy, density, hydrostatic pressure, cohesion and viscosity [
22,
35]. As the body is gradually immersed in water, buoyancy is created, progressively offloading immersed joints. It was reported that when the water depth is equal to the symphysis pubis, 40% of body weight is effectively offloaded, and if the depth is equal to the umbilicus or xiphoid, offloading increase to approximately 50% or 60% respectively [
35]. Thus, compared with land-based exercise, hydrokinesitherapy enables stroke survivors to support their body weigh more easily. It also allows patients to increase the active range of motion activities without causing pain, as well as strength and even gait training which present further difficulties on land [
35]. Furthermore, hydrokinesitherapy allows patients to enhance control of strengthening activities comfortably due to the viscosity of water [
36].
Another positive effect of water is the relaxation effect and the pain perception effect [
35]. Hydrokinesitherapy can inhibit the sensitivity of muscle spindles and skin. This results in a reduction of gamma fiber activity with a consequent reduction of muscle spasm and contractures, leading to remission of pain and muscle relaxant effects [
37]. All of these effects make water-based exercises a promising therapeutic intervention when targeting balance and walking ability improvement for patients after stroke.
A previous Cochrane review demonstrated that there is no firm evidence to support or refute the effectvieness of hydrokinesitherapy on ADLs for stroke patients [
29]. Multiple clinical studies have been reported since that systematic review was published. Emerging data has demonstrated that hydrokinesitherapy rehabilitation programs may have a positive influence on improvement of balance ability [
30,
38‐
40], muscle strength [
31,
38,
41], functional walking ability [
42], cardiovascular fitness [
32,
34], ADL and impaired mental health [
33] of stroke survivors. There is also study focused on this topic in progress [
43]. As a consequence of such, further evidence, the safety and clinical effectiveness of hydrokinesitherapy for patients with stroke should be reevaluated to provide further clinical evidence both for clinicians and patients. Based on all of above, the aim of this review is to elucidate whether hydrokinesitherapy rehabilitation programs are safe and beneficial to improve balance and walking ability for stroke survivors.
Conclusions
This systematic review and meta-analysis collated evidence from RCTs assessing the clinical effectiveness of hydrokinesitherapy on equilibrium function, walking ability and ADL for stroke survivors. Thirteen RCTs were included in this review involving 381 patients. All of the included articles used short-term (≤ 3 months) intervention. Based on our meta-analysis, hydrokinesitherapy showed the potential to provide positive benefits in improving the equilibrium function and walking ability of stroke survivors compared with non-water exercise or no treatment. However, no significant improvement was found in terms of ADL. There were no adverse events reported in all of the included trials.
Due to inherent imprecision (limited sample size of the participants) and publication bias (the number of studies included was less than ten for each outcome), the level of evidence was downgraded. And there was no reason to upgrade the strength of evidence. Finally, the quality of the evidence was downgraded to ‘low-quality’ for the primary outcomes of balance ability and walking ability. Based on sensitivity analysis results, the trial reported by Kim et al. [
39] had a significant impact on the results of the major pooled analysis. The reason we considered may be that the intervention in this studies was aquatic dual-task training in experimental group rather than only water-based exercise or water-based exercise plus land-based exercise without dual-task training [
39].
Strengths and limitations
The advantage of this review include its methodologically strong study design. First, a detailed search strategy was developed to obtain data by systematic searching different online electronic databases. Additionally, we developed and employed a structured study protocol to guide our search strategy, study selection, extraction of data and statistical analysis. Two reviewer authors independently screened, extracted, and evaluated the quality of data. Any disagreement was resolved by discussion and a final decision was determined by consultation with a third author. These methods reduced bias and transcription errors. Third, only RCTs were included in this review to ensure the design quality of the studies included. Finally, we clearly defined hydrokinesitherapy as a physical activity that is structured, designed, reproducible and implemented by a well-trained health care professional, rather than using a spa pool or bathtub to reduce the clinical heterogeneity.
However, there are also some limitations of this review. The first one we should note is that included trials demonstrated clinical heterogeneity in intervention test, intervention type, frequency and duration, which may result the evident heterogeneity. The type of hydrokinesitherapy used included aquatic physical therapy and aquatic treadmill exercise in the included trials. Both single hydrokinesitherapy, combinations of hydrokinesitherapy and land-based exercise were used in included trials. The intervention frequency ranged from 30 to 60 min per session and 2–6 times weekly. The intervention duration of the included studies ranged from 2 weeks to 12 weeks. Because of the variability in types of hydrokinesitherapy and measurement instruments of balance and walking ability, it was difficult to confirm a distinct relationship between specific types of hydrokinesitherapy and positive effect in balance function and walking ability.
Likewise, the instruments used to measure balance and walking ability in the included studies were heterogeneous. For the equilibrium function parameter, although 7 of the 13 included studies evaluated the effect of hydrokinesitherapy on balance ability and showed a significant difference between experimental group and control group. The variety of noncompatible measurement tools used (such as BBS, TUGT, FRT) results the difficulty to accurately calculate the effect sizes overall. For the walking function parameter, the same condition also existed. Few studies measured walk ability using the same measurement tools. Meanwhile, even though most of the measurement instruments, such as BBS, TUGT and FRT, had high validity and reliability, they were subjective which may result in the bias.
Additionally, it was impossible to blind participants and personnel in the hydrokinesitherapy program trial, thus performance bias is unavoidable. Another limitation was that the hydrokinesitherapy program used was of uniformly short duration without follow-up. Furthermore, methodological shortcomings, small sample size, a lack of reporting intention-to-treat analysis and limited of number of the included studies affected the credibility of our results. There were no adverse events reported in the included studies. However, we were greatly limited to determine the safety of practicing hydrokinesitherapy because of the poor and inconsistent reporting of adverse events. Therefore, caution is needed when interpreting the strength of the evidence.
Clinical relevance and future directions
Compared to land-based exercise or no treatment, hydrokinesitherapy is more effective in improving the balance function and walking ability of stroke survivors. This meta-analysis suggested that hydrokinesitherapy could be a feasible intervention for stroke survivors. This review provides evidence for both clinicians and stroke survivors to recommend application of hydrokinesitherapy. Although we were not able to identify some of the ‘grey’ literature, it was unlikely that there would be a significant impact on our results. We provided a template for future studies that could be used to guide further research.
There are still some issues that deserve attention to in future research. Appropriate intervention intensity and frequency should be used in future studies on this topic such as the recommendations by the WHO [
51] or the exercise training principles suggested by Campbell [
52]. Intervention should be no less than 6 months with adequate follow-up periods if possible. Measurement instruments which are more sensitive and objective should be used in future studies (e.g. three-dimensional gait analysis and Pro-Kin system). In addition, other rehabilitation outcomes concerning hydrokinesitherapy for stroke survivors, including fall rates, quality of life and remission of pain, also deserve attention. Participant experience in water before stroke, such as fear of water, ability to swim, limited experience of water buoyancy, should be a focus on in future trials. Finally, and most importantly, when reporting trials, the CONSORT guidelines should be used to allow better evaluation of the methodological quality. There is a clear need for well-designed, multi-center, large-scale trials to evaluate safety and clinical effectiveness of hydrokinesitherapy for people with stroke.
In conclusion, hydrokinesitherapy may improve balance ability and walking ability in stroke survivors. However, due to the differences in the styles, durations and frequencies of hydrokinesitherapy training, and the small number of included studies with small sample size, caution is needed when interpreting these results. Well-designed, large-scale, multi-center RCTs with adequate follow-up periods and standardized training protocols are needed to provide more reliable evidence in terms of the effects of hydrokinesitherapy on balance and walking ability in post-stroke patients.
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