Hydrotherapy is the use of different temperature, pressure and solute content of water, is the use of a variety of different temperature, pressure, composition of water, in different forms and methods (immersion, flushing, rubbing, drenching) on the human body or local action for the prevention and treatment of disease methods. The effect of hydrotherapy on the human body is mainly temperature stimulation, mechanical stimulation and chemical stimulation. There are immersion bath, shower, jet bath, whirlpool bath, bubble bath, high temperature bath, warm water bath, flat temperature bath and cold water bath, etc.. Hydrotherapy belongs to the category of physical therapy. The specific heat and heat capacity of water are very large, carrying heat more easily. The way of heat transfer is conduction and convection two. Water in addition to heat transfer, and mechanical effects, such as buoyancy, pressure and water, the impact of water jets. Water can also dissolve a variety of substances, drugs, these solutes can also play a therapeutic role. Hydrotherapy can be applied alone or for integrated treatment. Water therapy is simple and easy to use, unlike drug therapy as more side effects, but also unlike the mineral springs therapy is subject to the restrictions of the location, environment, conditions. First, the mechanism of hydrotherapy water therapy plays a therapeutic role in the underlying factors: 1, temperature stimulation The water temperature used is more than or less than the body temperature, warm and cold stimulation can cause the body to produce completely different nature of the response to the cold stimulus is rapid, intense; and the response to the warm stimulus is slower, not strong. The greater the gap between water temperature and body temperature, the stronger the response, the wider the area of temperature stimulation is the stronger the stimulation, the duration of the role in a certain time frame and the degree of response is proportional, such as cold stimulation in a short period of time to cause excitement, a long time after the paralysis, temperature stimulation repeated application of the response is weakened, so in the spa should gradually increase the intensity of stimulation to maintain adequate response. 2, mechanical stimulation hydrotherapy contains a variety of mechanical stimulation: (1) hydrostatic pressure stimulation in the ordinary tub, hydrostatic pressure of 40 ~ 60g / cm. patients in the tub when the chest, abdominal compression, breathing some degree of difficulty, the patient needs to breathe hard to compensate, which regulates the metabolism of gas. Hydrostatic pressure affects blood circulation, compressing the blood vessels and lymphatic vessels on the surface of the body, which can lead to an increase in the reflux of body fluids and cause the redistribution of body fluids in the body. (2) Impact stimulation of water flow Shower, direct spray bath, and needle shower all produce great mechanical stimulation. Clinical use of 2 to 3 atmospheres of omnidirectional water flow impact on the body, when the mechanical stimulation effect is dominant, while the water temperature may be lower, but cause significant vasodilation and excitation of the nervous system. (3) buoyancy effect According to Archimedes’ principle, an object immersed in water is subjected to an upward buoyancy force (the magnitude of which is equal to the weight of the object excluding the same volume of water). Based on the role of buoyancy, the activities in the water is more energy efficient. The weight lost by the body in water is equal to 9/10 of the body weight, and for patients with decubitus ulcers, burns and polyneuritis, immersion baths are used to eliminate the pressure on the body, while water sports can be performed with the help of water buoyancy. Patients with joint ankylosis can move more easily in water. Muscle spasm and atrophy can be treated with water gymnastics and massage. 3, chemical stimulation of the water used in the freshwater bath contains trace minerals. If a small amount of mineral salts, drugs and gases are added to the water, the stimulation of these chemical substances can strengthen the role of hydrotherapy and make the body obtain special therapeutic effects. Second, the advantages of hydrotherapy skin has a wealth of blood vessels and nerve endings. The skin has a large number of nerve endings of spinal nerves and vegetative nerves, the stimulation of the peripheral nerves can affect the function of the central nervous system and internal organs, to achieve anti-inflammatory, antipyretic, analgesic, sedative, hypnotic, excitatory, sweating, diuretic and Reduce muscle ligament tension, relieve spasm, promote metabolism, improve the regulation of the nervous system and other purposes: 1, the impact on the cardiovascular system This is determined by the temperature of the water, the duration of action and the intensity of stimulation. Whole body cold bath, the initial capillary constriction, heartbeat accelerated, blood pressure rose, but soon there is vasodilation, heartbeat slowed, blood pressure decreased, immediately reduce the burden on the heart. Therefore, it is believed that cold improves the capacity of the heart muscle, slows down the heartbeat, and improves the nutrition of the heart muscle. When the whole body is bathed in warm water (36-38℃), peripheral blood vessels dilate, pulse rate increases, blood pressure decreases, and blood redistribution in the body. However, if the blood redistribution changes sharply, some symptoms of reduced cerebrovascular circulation will appear, such as facial color change, heavy head, dizziness, headache, tinnitus and blurred eyes, etc. It is especially common in patients with weakness, anemia or hypertension and tendency to cerebral congestion. Therefore, close attention should be paid to the patient to avoid the above symptoms as much as possible. During a full-body hot bath (above 39°C) blood pressure starts to rise, then falls, and then rises again. First, the blood vessels under high temperature spasm, followed by vasodilatation, there is an accelerated heartbeat, increased burden on the heart, healthy people and those with good compensatory capacity of the heart, this performance is obvious. Do not feel the warm bath has little effect on the human cardiovascular system. 2, the impact on the muscular system is generally believed that a short period of cold stimulation can improve muscle stress capacity, increase muscle strength, reduce fatigue; prolonged cold stimulation can cause a decrease in tissue temperature, muscle stiffness, resulting in activity difficulties; warming effect can release muscle spasm, improve muscle work capacity, reduce fatigue, while under the effect of heat, vasodilation, increased blood oxygen and metabolic overdrive, conducive to muscle fatigue The elimination of. 3, the impact on the urinary system The cold stimulus reduces the volume of urine, cold bathing with less sweating, which makes the volume of urination relatively increased. Warm stimulation can cause vasodilatation of the kidneys and enhance diuresis, but in a hot bath, the volume of urination decreases due to heavy sweating. After a long warm bath, blood circulation improves, and the amount of sodium and urea excretion increases during the day and night. 4, the effect on sweat gland secretion After the hot bath, sweat gland secretion is enhanced, discharging a large amount of sweat, the loss of a large amount of sodium chloride, weakness, individual patients sweating too much, should be supplemented with salt water. With sweating harmful metabolites and toxins discharge increased. This results in fluid loss, blood concentration, and water in the tissues entering the blood vessels, promoting the absorption of exudate. 5, the effect on respiration Instant cold stimulation deepens inspiration, and sometimes also respiratory arrest and deep exhalation, and the respiratory rhythm accelerates and deepens. Thermal stimulation can cause fast and superficial respiratory rhythm, and slow down respiration after a long warm bath. 6, the effect on the nervous system, blood, metabolism whole body warm water bath can cause the increase of body fluid viscosity, specific gravity, hemoglobin increased by 14%, red blood cells increased by more than a million, white blood cells also increased, the oxidation process accelerated, the basal metabolic rate increased. Cold water bath increases fat metabolism, gas metabolism and blood circulation, promotes the absorption of nutrients, and may excite the nerves. Cold water spraying head and face is commonly used in folklore to help comatose people wake up. Hot water bath (40 ℃ or more) after the first nerve excitement, followed by general fatigue, weaker, and desire to sleep.