Effects of hydrogymnastics with dynamic exercises in movement on the body balance of elderlyl

Corresponding address: Pedro Paulo Deprá – Av. Colombo, 5790, Zona 7, Maringá (PR) – Zip Code 87020-900 – Telephone: (41) 99723-4394 – E-mail: ppdepra@uem.br – Finance source: CNPq, Finep, SETI-PR – Conflict of interests: Nothing to declare – Presentation: Sept. 10, 2016 – Accepted for publication: June 15, 2017 – Approved by the Comitê de Ética em Pesquisa com Seres Humanos (COPEP) of the Universidade Estadual de Maringá (UEM), under the protocol n° 096. DOI: 10.1590/1809-2950/16906724032017

El equilibrio postural fue mensurado por el comportamiento Effects of hydrogymnastics with dynamic exercises in movement on the body balance of elderlyl

INTRODUCTION
The population of people aging 60 years or more has been increasing. According to the United Nations, between 2015 and 2030, it is estimated that the number of people around the world aging 60 or more will grow 56%, from 901 million to 1.4 billion. During the next 15 years, it predicted that the number of these people will grow quicker in Latin America and Caribbean, having a predicted increase of 71% in the population aging 60 years or more 1 . However, such longevity needs to be followed by habits that prevent elderlies from adverse situation that compromise their quality of life. As an example, the impact of balance loss in the elderly can compromise their functional independence, putting them under the risk of suffering falls 2 .
Along with the ageing process, the visual, vestibular, and somatosensorial systems can be affected and many phases of postural control can be suppressed, reducing the system's compensation ability, leading to an increase in postural instability 3,4 . In this sense, the practice of physical activity, which considers the recommendations regarding the kind, intensity, frequency and duration, can avoid physical incapacities and functional losses that happen to elderly 5 and can contribute to a better quality of life 6 .
According to Simoons and Hansen 7 , due to the prevalence of mortality associated with falls in the elderly population, older adults tend to restrict their mobility to avoid the occurrence of a fall. By restricting activity, elderlies can submit themselves to a vicious cycle of voluntarily restrictive activities, which, in its turn, leads to a reduction of functional mobility, which results on restricted activities 7 .
Hydrogymnastics has been playing an important role on the health care performed to elderly people, by promoting the improvement of their independence and functional abilities 2 . The therapeutic benefits of water have been commonly attributed to its physical properties such as buoyancy, pressure and heat exchange 7 . However, water exercises for the elderly population enable them to perform big movements without the risk of falling or getting injured and help to keep an independent posture 8 . According to Avelar et al. 8 , water has a viscosity that allows the movement to be done slowly and, thus, the individuals have more time to create and develop answer reaction mechanisms.
In literature, there are hydrogymnastics programs reported in which the classes are 50-60 minute-long, focusing primarily on stationary exercise. In the last decade, it was possible to observe new suggestions using dynamic exercises with movement in the liquid mean 11,12 , a fact that broadens the possibility of interactions with the medium for the participants. Water resistance, the dimension and speed of the body immersed in this fluid promote the drag force, which imposes more restrictions to the movement and requiring, thus, constant postural adjustment 13 .
The aim of this study was to assess the effects of a program comprised of classes with 70-80% of its exercises performed with movements on the elderly body balance.

METHODOLOGY
This quasi-experimental outlining study was comprised of 37 elderly people, being 05 men and 32 women, aging from 60 to 80 years. Two sample groups were composed, being one of them the experimental (EG), n=27, with an average age of 67.33±5.53 years, average height of 1.56±0.07 meters and average body mass of 65.43±12.09 kg, and the other, the control group (CG), n=10, with an average age of 67.74±7.24 years, average height of 1.59±0.07 meters and average body mass of 73.62±12.17 kg, comprised by elderly who did not practice hydrogymnastics. The EG had never practiced hydrogymnastics and the CG did not practice physical activities. The study was initially comprised by 51 elderlies, and had sample loss of 6 elderly from the EG and 8 from the CG.
The convenience sample of EG was composed by elderly people enrolled in a hydrogymnastics program, belonging to an extension project of the Universidade Estadual de Maringá, PR. Inclusion criteria were elderly aging from 60 to 80 years who voluntarily accepted to join the study after the promotion for external community to take part in hydrogymnastics classes of an university extension project. The participation of the EG happened after a medical approval. The elderly from both groups did not perform any other physical activity during the study period.
CG was selected intentionally and non-probabilistically by the easiness of contact to the people aging from 60 to 80 years and who did not practice hydrogymnastics.
The project was approved by a Committee of Ethics on Research with Human Beings of the Universidade Estadual de Maringá, CAEE (no. 0047.0.093.000-10). The participants signed the Informed Consent Form in order to join the study.
Before and after the experimental protocol, EG and CG elderly were evaluated regarding the center of pressure (COP) variables, which are the medial-lateral width, anterior-posterior width, total movement and COP area 14 .
Body balance in elderly was evaluated by the analysis of the COP behavior using a force platform (EMG System do Brasil®). Sample rate was 100 Hz and the acquisition period was 30 seconds 15 . Through the Biomec 400 Software, the values for COP variables were extracted.
During the measurement of body balance markers, each subject was standing on both feet on the platform, in the orthostatic position, placing the feet at the same distance from each other than the shoulders, with relaxed and placed along the body arms, fixed gaze on a point at the wall in the same height than the eyes, two meter-distant from the force platform, data gathering pre and post-intervention was done twice by each volunteer, with the eyes open and closed. From these data, the average for each verification was estimated.
To verify the effect of vision on balance, the Romberg quotient was used. This quotient is a ratio of the values for the variables obtained in the condition 'eyes closed' and 'eyes open'. Romberg Quotient is measured by the expression RQ=EC/EO. This quotient's null hypothesis is a value equal to 1, which corresponds to no contribution of the vision to posture stabilization 16 .
The classes were given by the hydrogymnastics trainee of the extension project Avaliação, Prescrição e Orientação de Exercícios Físicos para Populações Especiais e Atletas Universitários (Assessment, Prescription and Guidance of Exercises for Special Populations and University Athletes), which helped elderlies when going in and out the pool, following the class development close to the elderly for more safety.
The EG was submitted, throughout 16 weeks, to a hydrogymnastics program, having 50 minute-long sessions twice a week, performed in alternate days, in a heated swimming pool at the temperature between 29 and 30 ºC and 1.25 m deep. During the class, the activities were performed with all elderly people (n=37), with no subgroup division.
Each class was divided into three parts, 10 minutes of warm-up, 30 minutes for the main part and 10 minutes of relaxation and/or stretching (Chart 1). During the warm-up, the time spend in each exercise varied around two minutes, according to the exercise's intensity. Relaxation was used only in high intensity classes.
For the statistical analysis, the exploratory analysis was performed to assess the normality of data distribution using the Shapiro-Wilk test. In descriptive statistics, the average and standard deviation for the results that showed normal distribution were calculated. For the results that showed lack of normality, the median and interquartile range were estimated.
In the comparison intragroup (pre x post) involving the normal distribution, the dependent Student t-test (paired) was used, while the Wilcoxon test was used for the variables that do not involve normal distribution. In the comparison between groups (pre x pre and post x post), the Levene's test for equality of variances, and the independent Student t-test (normal distribution) and Mann-Whitney U test (non-normal distribution) were used.
The significance level adopted for all statistical tests was of p<0.05. To portray the amplitude of the effect in intragroup and intergroups comparisons, we used the Cohen value (d) for parametric distribution and the value (r) obtained by the division of z value of the test by the square root of the total value number. Strong effect in the intragroup and intergroups comparison is attributed to values above 0.4 17 .

RESULTS
The results of COP variance in pre and post tests are shown in the Tables 1 to 4. The exclusion criterion was the elderly's absence in three classes, without justification.

COP width in the medial-lateral direction
The COP medial-lateral width in the open eyes condition was higher for the post-intervention moment than in the pre-intervention one. Romberg Quotient for the EG at the pre-intervention moment was 1.06 (±0.33) and at the post-intervention it was 1.01 (±0.29). It was observed no difference between the pre and postintervention moments for the EG Romberg Quotient in the medial-lateral width.

COP width in the antero-posterior direction
When the antero-posterior width was compared in both groups (intragroup), we observed no statistically

Total COP movement
Total COP movement in the eyes open and closed conditions showed reduction at the post-intervention moment for CG as well as for EG. At the postintervention moment in both conditions, EG showed total movement smaller than CG.

COP Area
The COP area in the eyes open condition of CG was higher at the post-intervention moment than at the pre-intervention one. No differences were observed between the groups for the variable COP area. No differences were found for the COP area of the EG.

DISCUSSION
COP results obtained in this study showed that hydrogymnastics enabled the improvement of the elderly's body posture after the intervention period. Such improvement was seen in a reduction of the total movement and the maintenance of antero-posterior width and COP area in the eyes closed condition. The results shown by the elderly participants in the hydrogymnastics training were highlighted when compared to the elderly people in the CG. After the intervention period, the CG showed an increase in the COP area, that is, a broader dispersion of COP data 15 .

The effects of hydrogymnastics on the total COP movement
The results seen for the variable total COP movement showed that the EG had a significant difference in relation to the CG in the eyes open and closed conditions. EG showed post-training movement values about 30% lower than CG in the eyes open condition and 40% lower in the eyes closed condition.
Generally, when the visual information is removed, the proprioceptive information is not enough to allow the postural control to have the same behavior 18 . However, in our study, the EG, even with reduced visual information, showed better postural control that the CG. The same happened in the study by Oliveira 19 in which the aim was to assess the biomechanical characteristics of elderly balance, highlighting a better balance in the female group and among the ones who practiced physical activities. In that study, the situations where there was less stability was with the eyes closed.

The effect of hydrogymnastics on the COP width
The results for the antero-posterior width showed that the EG had a significant difference, 23.5% smaller in relation to the CG at the post-intervention moment in the eyes closed condition. Positive contributions of the water exercise for the reduction of postural instability were also shown in the work by Suomi and Koceja 20 , in which for the medial-lateral as well as for the antero-posterior, the group who performed water exercises showed reduction of post-intervention postural oscillation. In literature, it is possible to see results of interventions that led to an increase in the averages of the COP variables. When studying the effect of Tai Chi Chuan on the balance and mobility of individuals with multiple sclerosis, Averill 21 observed an increase in the speed and COP excursion after the intervention, when the subjects performed a meditation standing posture with arm movement. According to Averill 21 , instead of the prediction of increase of postural oscillation because of a lesser CNS control due to the ageing process, the increase in postural oscillation can really be a beneficial adaptation to increase the amount of sensorial information available for the CNS.
Besides, according to Averill 21 , the increase in speed and COP excursion may have happened because the participants felt more self-assured moving within their balance limits.
Similar results to the ones found in our study were described by Maejima et al. 22 . As an effect of intervention, COP postural oscillation increased significantly. According to the authors, this increase is a function acquired to control static balancing. To verify the effect of vision on balance, Maejima et al. suggested the use of the Romberg quotient. In this study, we had values close to 1 for the variable medial-lateral width, in pre (1.06) and post (1.01) moments, showing that in the comparison between intervention moments, the vision had less influence on the results for the medial-lateral width, thus, demonstrating that possible alterations come from the proprioceptive and vestibular system. Therefore, despite the low difference found in the eyes open condition for the variable COP medial-lateral width, we highlight that this information is important, since it agrees with Averill 21 , whose strategy is that elderly people, for trusting more, begin to explore the limits of their base of support.

The effect of hydrogymnastics on the COP area
Regarding the COP area, it was observed a difference between the pre and post-intervention moments only for the CG. This result shows that this variable increased 76.2% in the elderly who did not practice hydrogymnastics. Such result is similar to the study by Freitas Junior 23 that analyzed the postural oscillations of young, adult and elderly people, and observed significant differences among the visual conditions, with a bigger COP are in the eyes closed condition.
Paulus apud Aoki 24 affirms that the visual system has a very important role on the maintenance of a stable posture, and it has been posited that reduced visual function firmly affects postural control. With the reduction of visual information, CG showed more difficulty in keeping postural control at the postintervention moment for the COP area variable.
Thus, the increase in COP area in the CG eyes closed condition can be an indicative of the importance of promoting actions to encourage regular and continuous hydrogymnastics practice for the elderly population as a way of maintaining balance and, consequently, other benefit associated to the practice of physical exercises, as the maintenance of movement width, musculature strengthening, and cardiorespiratory conditioning, performed safely 25 . This may provide the elderly more autonomy for the realization of activities of daily living (ADL), for their leisure activities and independence, thus impacting general well-being and quality of life 26 .

Study limitations and suggestions for further investigations
One of the study's limitations was not monitoring physical activities of daily living (ADL) of the CG and EG, and the reduced number of male elderly people. This procedure would add more information to the interpretation of the phenomenon of elderly adaptability to the training based on water exercises.
We suggest further investigation verify the elderly's health state, the fall frequency and that a questionnaire on quality of life be applied. Concerning the intervention, we suggest that the effects of weekly frequency and duration of the hydrogymnastics class on body balance is verified.

CONCLUSION
Based on the results, it is possible to conclude that water activity improved the body balance of the EG, the total COP movement and antero-posterior width with closed eyes, of elderly people who practiced hydrogymnastics after 16 weeks of intervention focused on dynamic movement exercises.
Thus, we conclude that hydrogymnastics practice focusing on exercises with different movement possibilities can change significantly the postural balance rates.