Exercise physiology in swimming pool and cardiovascular system
During the last 10 years, the area of exercise physiology has developed very much, especially not only with a sports approach, but also a clinical, but the cardiovascular physiological changes generated by immersion exercises have not been studied much, for the same, we have prepared this post with the most current concepts on this subject.
The physico-thermal principles of water are largely responsible for the physiological changes of the organism in immersion
When human beings immerse themselves in the aquatic environment, they experience the action of new physical laws, which modify their behavior, which are the basis of the use of aquatic therapy in various physical dysfunctions, which means that the sum of these inherent forces in immersion, provides an appropriate physical means for performing assisted or resisted exercises of the limbs, minimizing the load on joints and muscles.
Therefore, hydrostatics physical principles (hydrostatic pressure, Archimedes’ law and metacentric effect), hydrodynamics (hydrodynamic resistance to movement) and hydrokinetics (water movement and turbulence), are the triggers of physiological adaptations in the dive as well as the temperature of the water.
In this publication, we will not analyze these physical principles, but the exercise physiology and the changes that are provoked in the cardiovascular system, when performing physical exercise in a temperate pool.
Hydrostatic pressure and exercise physiology in pool on the cardiovascular system
Hydrostatic pressure, a determinant of the floating force, causes important effects on peripheral circulation and cardiac function, especially in full immersion (at the level of the seventh cervical spine), resulting in a change in the blood distribution, with a renal response and increased venous return, from the periphery to the heart, facilitating the work of the cardiovascular system; with an increase in plasma volume, which decreases hemoglobin and hematocrit.
Therefore, when immersed in water, the hydrostatic compression is exerted perpendicular to the surface of the body, modifying the venous transmural pressure, in which the capacity of the normally distended veins diminishes, and at the same time, the spaces Interstitials are compressed, causing an immediate displacement of blood and a slower interstitial fluid, especially useful in transudate edema resulting from prolonged orthostatism or vascular alterations.
The veins of the lower limbs and abdomen are compressed by hydrostatic pressure reaching 15 mm Hg in the thoracic and abdominal cavity, considering that the atmospheric pressure is exerted on the head and neck that are not submerged and is transmitted through of the bronchi and bronchioles within the alveoli, triggering an imbalance between the pressure exerted on the thoracic cavity and the low air pressure in the alveolar space, redistributing a blood volume of 700 ml towards the central circulation and the heart accepts 200 ml of this, increasing the venous pressure and therefore the venous supply to the right cavity.
In a complete immersion, the pressure exerted by the water decreases the thoracic perimeter from 1 to 3.5 cm, while the abdominal perimeter decreases from 2.5 to 6.5 cm, because it is less rigid, thus there is a displacement of the blood volume, which induces an accumulation in the intrathoracic reservoirs, increasing the intraauricular pressure and elevation of the phlebostatic plane.
The sinus intra-carotid pressure. What causes in the cardiovascular exercise physiology?
As mentioned above, this abrupt elevation will cause an increase in systemic blood pressure, which will be followed by normalization of tension, or even slight decrease, therefore, the corresponding increase in sinus intracarotid pressure will trigger the following results:
1- Inhibition of sympathetic control of the cardiovascular system, initially producing a slight bradycardia, decreasing 60% of the heart rate (HR), with respect to the heart beat in normal conditions and later normalization of the HR, decreasing the peripheral vascular resistance and inhibiting renin secretion, with decreased aldosterone.
2- Distension of the atrial wall, causing an increase in serum levels of atrial natriuretic peptide (ANP) and dopamine, maintaining even 15 minutes’ post subtotal immersion; this peptide is vasorelaxant, aldosteronic antagonist and renin inhibitor, causing a marked increase of diuresis and natriuresis (elimination of sodium from the urine), accompanied by a smaller increase of the urinary excretion of chloride, potassium, calcium, phosphate and magnesium.
This is the explanation why, we are so keen to urinate, when exercising in the pool, since the diuresis increases significantly five minutes after the dive and can remain higher than normal, up to the fifth hour, which is due, not only by the displacement of the blood mass and the consequent atrial dilatation, but also due to the interstitial liquids reabsorbed by the effect of the hydrostatic pressure, that cause hemodilution.
What are the major hemodynamic changes during immersion in the thermoneutral water?
A 30-50% increase in cardiac output has been reported when an individual is submerged at rest, a consequence of a decrease in HR mediated by two factors: 1) Increase in systemic blood pressure and 2) increase in systolic volume (Being the main factor), reaching 35% more than on earth, under conditions of rest, caused by a small increase in thoracic blood volume.
In addition, during submaximal exercise in water, there is a 40% increase in VO2máx., and in maximal intensity exercises, there is no new increase in systolic volume, explained by the displacement of peripheral blood volume towards the heart, when it is in rest in the water, reducing the amount of blood available, to be changed centrally during exercise.
Also, because left ventricular diastolic volume at rest, within the water, is close to the maximum, reducing the capacity to increase systolic volume more, with exercise and time of cardiac filling is reduced.
The increase in systolic volume during immersion is attributed to Frank-Starling’s mechanisms, as a result of a higher preload and not due to the increase in left ventricular emptying.
On the other hand, blood pressure does not change significantly, what does occur is an increase in peripheral blood flow, by a decrease in total peripheral resistance, as there is a change in transcapillary fluid and a decreased peripheral vascular volume.
The large thoracic blood volume, increases the distension of the myocardial wall, which, in turn, reduces sympathetic nervous activity. Also, the large final systolic volume in the left ventricle implies a reduction of contractility and increase of afterload; it is worth mentioning that the magnitude of the cardiovascular responses depends on the level of immersion.
Hemodilution: Exercise physiology in swimming pool
After immersion, there is an early and gradual decrease in the concentration of hemoglobin, albumin, number of cells and blood viscosity, whose main reason for this movement of extracellular fluid is the action of hydrostatic pressure of water on the limbs and abdomen.
The decrease in plasma viscosity is also probably caused by the displacement of the liquid between compartments.
Application of cardiovascular effects of exercise in water
As mentioned, when exercising in water, venous return increases by hydrostatic pressure, bringing more blood to the heart, elevating preload, being very beneficial in people with congestive heart failure, decreasing peripheral edema, regulating the sympathetic tone by the ANP and increase systolic volume.
On the other hand, exercise generates a shear stress, on the endothelium, which triggers the release of nitric oxide (NO), causing a vasodilation, reducing total peripheral resistance, favorable for hypertensive people, and stimulating diuresis (urine) and natriuresis (elimination of sodium).
As a consequence, cardiovascular resistance is greater, by improving the redistribution of plasma fluids, which allow to work at higher intensities, without fatigue, because there is no joint impact and movements are easier to perform, with lower torques.
But when you leave the person after a Kaenz session in the pool, you will notice that the cardiovascular system worked quite hard and all of its muscles, something unthinking on land, especially for sedentary people who have some pathology.
We know that you love water and that the aquatic environment has great potential to improve the health and quality of life of people, therefore, we invite you to become a Kaenz Therapist, expert in prescribing physical exercise in swimming pool. Do you want to know more?
Finally, continue training yourself in this fascinating area, through scientific articles of a level of evidence Ia and Ib of the Oxford Scale of the last 5 years, on aquatic therapy and pool exercise in the Research category of our blog.
Best regards and we are attentive to your comments.