Hydrotherapy is widely used for the treatment and rehabilitation of patients, but it can also be applied to prevent diseases in healthy people. This blog investigates the health effects of water immersion, a form of hydrotherapy, and the mechanisms by which the properties of water elicit such an effect.

For this blog I summarise an excellent Korean review written by Jiyeon An, Insook Lee and Yunjeong Yi in February 2019, referencing 46 different studies and published on 10 April 2019. Emphasis is mine.

Hydrotherapy is a field that pursues disease treatment or health effects using various properties of water for therapeutic purposes and is used synonymously with water therapy, aquatic therapy, pool therapy, and balneotherapy (hot spring and spa).

Hydrotherapy is a therapeutic modality that maximizes the characteristics and advantages of water and is considered in clinical and alternative medicine to have an excellent therapeutic effect, with few adverse effects.

Water offers various advantages, including being abundant; not physiologically irritating; and having an excellent solvency, excellent viscosity, high heat capacity, and high heat conductivity. In addition, the density of pure water is similar to the average density of the water present in the human body.

Accordingly, the present study aimed to conduct an integrative literature review to investigate the effective mechanism of water immersion to determine the effect of hydrotherapy using only the properties of water.

The most apparent conclusions regarding the physiological effects of warm water immersion were that it elicited the same effect as exercise to improve cardiopulmonary function. These hemodynamic effects of warm water immersion were explained in each study as follows.

Bailey et al. compared the exercise group with a control group to estimate cardio-respiratory function (maximal oxygen consumption) during water immersion. Surprisingly, cardio-respiratory fitness in the warm water immersion group was like that of the exercise group on land.

Hu et al. also explained that improvements in arterial stiffness due to an elevated core body temperature could also improve cardiovascular function by decreasing vascular resistance and increasing blood flow.

Bunt et al. explained that warm water immersion may reduce the progress of vascular pathologic changes, such as atherosclerosis. Furthermore, warm water immersion increased oxy-haemoglobin levels to improve tissue oxygenation and contributed to an improved short-term brain function by increasing the levels of substances involved in brain-cell genesis.

Wijayanto et al. explained that the improvement of blood flow rate by warm water immersion therapy can, in turn, improve the function of important organs such as the brain by facilitating the transport of substances in the blood.

In other articles, partial immersion applied to elderly subjects was found to be effective in partially improving the quantity and quality of sleep.

The health effects of hydrotherapy generally appear as thermal, mechanical, and chemical effects, either alone or as mixed effects. Thermal effects are elicited via heat (35–40 °C), body temperature (32–34 °C), or cold (8–10 °C) therapy.

Heat therapy is typically explained by vasodilation and blood flow facilitation effects, while cold therapy is typically explained by vasoconstriction and pain reduction effects. Mechanical effects can be explained by the properties of water, such as buoyancy, hydrostatic pressure, and resistance, where the effect primarily appears when hydrotherapy is provided via immersion therapy.

Buoyancy represents the force that opposes gravity, and when the body is partially or fully immersed, pain reduction and improvement in exercise ability occur due to the reduction of stress or application of weight to specific body parts.

Hydrostatic pressure promotes blood flow by varying the pressure exerted on the body according to the immersion depth, which results in increased blood flow to major organs (the heart, brain, and lungs) or the promotion of diuretic action.

Resistance is the force that opposes bodily movement and is associated with the viscosity of the water and results in muscle strengthening.

Moreover, environmental effects can further enhance the psychological effects. Combining complimentary alternative therapies, such as massage, relaxation, music, or aromatherapies, can also induce health effects by increasing the body’s natural healing ability.

Exercise therapies or physical activities in water, including swimming, walking, and aerobics, are also combined for the purpose of physical therapy.

Hydrotherapy has been applied in combination with various therapies, such as physical therapy, rehabilitation therapy, disease treatment, and health promotion programs. Systematic reviews, review studies, and meta-analyses have been conducted on studies related to the application of hydrotherapy for symptom alleviation in patients with musculoskeletal diseases (such as arthritis and fibromyalgia), functional improvement in patients with neurological disorders (such as stroke and muscle paralysis), and rehabilitation of patients with acute injury in sports medicine. In addition, recent studies have assessed the psychological effects of hydrotherapy, such as mental relaxation, mental fatigue, quality of life, and depression/stress.

With the large number of studies on the psychological and physiological effects of hydrotherapy, the need to expand the application of hydrotherapy and establish practical guidelines for the various clinical applications has been highlighted.

“If hydrotherapy has a positive effect on health promotion, as well as on disease prevention, treatment, and rehabilitation, then its application as an effective health promotion program can be expected.”

In the field of health, hydrotherapy is commonly applied as local cold or heat therapy, and in particular, its effectiveness in reducing musculoskeletal symptoms and promoting post-traumatic recovery has been confirmed. The advantages of water are very diverse and effective. There is evidence for the application of hydrotherapy for people with disease, but there is no such evidence for healthy people. Hydrotherapy for healthy people can be used as a health promotion program in the community and may be used as a new health service to achieve therapeutic effects beyond the scope of alternative medicine.

In conclusion, the physiological changes induced by warm water immersion, such as vasodilation, increased blood flow, reduction of arterial stiffness, vascular endothelial function, oxygenation, and decreased sleep-related stress, may result in improvements in the cardiovascular function. These physiological changes due to water immersion are similar to the cardiovascular effects of physical activity.

In contrast, cold water immersion reduced the nerve conduction velocity, which raised the pain threshold to promote pain control. Moreover, it also increased the blood pressure and heart rate variability, the latter of which is an indicator of sympathetic activity. One article used repeated cold-water immersion and identified 26 °C as the appropriate temperature for insulative cold adaptation, which is significantly warmer than an ice bath.

Immersing yourself in an Aussie Spa is now proven to be much better for you than you originally thought!

Yours in health and wellness