Cardiovascular disease (also referred to as CVD) is a major global health concern, that is becoming more common worldwide. Maintaining a healthy lifestyle and performing physical activity on a regular basis are some of the well-known preventative measures against cardiovascular disease. [10, 18]. However, some of the traditional land-based exercise programs may be challenging for individuals suffering from a cardiovascular disease, due to underlying health conditions .
As CVD prevalence is growing worldwide, the need for safe, enjoyable, and effective exercise options to help improve the health and wellbeing of adults is also on the rise. Aqua fitness offers a promising alternative, offering a low-impact exercise option that could be a safe and effective alternative for CVD patients. In the following article, the benefits of aqua fitness as a form of exercise for CVD patients will be evaluated based on studies conducted on the subject within the past years.
Recent studies have shown that aqua fitness can improve cardiovascular health as well as physical fitness in CVD patients [10,23]. For example, a study researched the effects of aqua fitness on inflammatory markers related to CVD in obese women. The semi-experimental study included a 10-week aqua fitness program with a pre and post-test design which found a positive impact on not only cardiovascular inflammatory markers but also other CVD risk factors such as blood pressure, obesity, and lipid-profiles . Similarly, a meta-analysis of randomized controlled trials also reported that aquatic endurance exercise was found to improve lipid-profiles and particularly benefited women, middle-aged participants, and patients with high cholesterol .
As we know, being active plays an important role in maintaining healthy cholesterol levels. The results from the aforementioned studies indicate that aqua fitness could be considered part of a healthy exercise habit for CVD patients.
2. Closely associated diseases
Diabetes and hypertension are two worldwide health issues that are both major risk factors for CVD. Hypertension alone can be considered one of the strongest if not the strongest risk factor for almost all types of CVD. [9,12] Type 2 diabetes and hypertension often coexist increasing the risk of CVD. Adults with diabetes are at significant risk of both hypertension and CVD. Some sources claim a 2-4 times higher risk of developing CVD in adults with diabetes than those without. [19,6] The impact of aqua fitness on managing these risk factors will be reviewed in more detail within the following paragraphs.
Diabetes is a common disease worldwide that is closely associated with cardiovascular complications. Therefore, cardiovascular risk factors are often common in individuals with diabetes due to several reasons, such as the metabolic nature of the illness putting them at greater risk of developing CVD. [16,14] A systematic literature review found that approximately 32.2% of all people with type 2 diabetes are affected by CVD resulting in CVD accounting for almost half the deaths during the study period. 
Research conducted has shown positive outcomes of aquatic training in patients with diabetes and cardiovascular diseases. For instance, a study was conducted on aquatic exercise with patients that suffer from heart failure and type 2 diabetes. In the study, aquatic exercise was found to be a safe and effective way to enhance physical and metabolic functions in participants. These results were found by performing several assessments such as questionnaires, walk tests and venous blood samples measuring blood sugar levels, insulin levels and cholesterol levels. However, the results were not compared with land-based exercise options meaning aquatic exercise cannot be argued to be superior to land-based exercise, but instead a justified alternative. 
Another study was conducted on the efficiency of aquatic exercise training in comparison to land-based programs for individuals with heart failure. The study found positive outcomes in both forms of exercise, as exercise capacity, muscle strength, and quality of life improved in the individuals. The results suggested aquatic training can be an alternative form of exercise for individuals that are unable to participate in land-based exercise due to other reasons. 
Despite the positive results found regarding aquatic-exercise in patients with heart failure, some parties may disagree. A research article and the 2020 European Society of Cardiology guidelines in sports cardiology and exercise in patients with cardiovascular disease both evaluated several different forms of exercise in patients with heart failure and stated that aquatic exercise is not necessarily a first-hand option due to the increase in the central blood volume and cardiac preload caused by hydrostatic pressure that some patients may not be able to tolerate. However, this could highly depend on the degree of heart failure that the patient suffers from, since both sources also state that positive results have been found in recent studies. [13, 3] For patients with heart failure, and indeed any form of CVD, a valuation of a qualified healthcare professional should be sought.
Hypertension is regarded as the leading preventable risk factor for cardiovascular disease and premature mortality . The World Health Organisation states that an estimated 1.28 billion adults aged 30-79 years old are affected by hypertension and are often unaware of it . A meta-analysis of randomized controlled trials studied the effects of regular aquatic-exercise on blood pressure and found that aquatic exercise can have a positive effect on lowering blood pressure, specifically amongst participants that suffered from high blood pressure initially. Significant changes were found in both systolic and diastolic blood pressure. 
Another study examines the effects of land-based exercise versus aquatic exercise on blood pressure levels at rest and assessed post-exercise hypotension following both forms of exercise. The participants in the aquatic exercise group had a lower baseline blood pressure during the day and their post-exercise hypotension decreased quicker as well as lasted longer. .
To support the previous findings, the effects of aquatic exercise on post-exercise hypotension were investigated in a systematic review and meta-analysis. The review found that aquatic exercise showed a higher post-exercise hypotension effect compared to land-based exercise and resting conditions . Post-exercise hypotension can be an important factor to value when trying to manage high blood pressure since it is an immediate short-term benefit that can be attained by just a single session of exercise with benefits that can last up to 24 hours .
3. Mechanisms of an aquatic environment
Although aqua fitness has shown promising results in improving cardiovascular health with patients that suffer from CVD as well as healthy adults, the exact mechanisms responsible for these benefits still need further research. Some studies have suggested that factors such as water pressure, temperature, and buoyancy may play an important role in improving cardiovascular health. [21,2]
A meta-analysis of randomised controlled trials suggests that the beneficial effects of aquatic-based exercise for men with coronary artery disease can be partially explained by the water pressure on the peripheral veins which helps improve blood flow back to the heart and leading to an overall improvement in the functioning of the heart. The same research discovers the benefits of aquatic exercise in reducing body fat and improving muscle strength due to the natural resistance that water provides during movement. 
Other research has shown that water-based exercise can be seen to have a beneficial effect on the reduction of blood pressure through several different complex physiological mechanisms, such as the decrease in the peripheral vascular resistance, suppression of the renin-angiotensin system as well as the cardiopulmonary and baroreflex activation system. The renin-angiotensin system is a hormonal system critical for regulating blood pressure by controlling the amount of fluid and salt in our body. The cardiopulmonary system is made up of our heart and lungs and the baroreflex system helps regulate our blood pressure through baroreceptors located in blood vessels near our heart. [20,11,4, 8]
Based on the research analysed, we could argue aqua fitness to be a safe and effective form of exercise for most individuals for managing and preventing cardiovascular disease. In addition to minimizing several risk factors of CVD, incorporating aqua fitness into an exercise routine seems to improve not only cardiovascular fitness but overall quality of life as well. The exact mechanisms that lead to these positive effects still need further research. Nevertheless, the benefits of aquatic exercise cannot be ignored and we at Hydrohex are happy to be a part of providing a new and fun aquatic exercise solution for everyone to enjoy to help lead healthier lives.
Disclaimer: This article is written by an employee at Hydrohex. The article has been written from an objective viewpoint, but naturally, the author cannot guarantee their absolute objectivity due to being aligned with an aqua fitness startup. At Hydrohex we care for your safety and wellbeing which is why we recommend consulting with your doctor before engaging in our exercise classes as a precautionary measure.
About the author: Ella Cummings is interning at Hydrohex as a Business Development intern as part of her Bachelor of Business studies. With a previous career in nursing, she has built up strong expertise working with cvd patients. Ella brings numerous transferrable skills to the team, such as her expertise in health through her work, academic knowledge through education past and present, and understanding of wellbeing through her background as a fitness instructor.
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