Hydration and mineral salts: role and functions

Role of hydration

Hydration has always played an important role in sports performance, injury prevention and recovery after training sessions or competitions, both for athletes involved in sports or competitive competitions and at an amateur level. Therefore, it is extremely important that both coaches and athletes clearly understand the mechanisms and physiology of this mechanism, in order to improve the sportsman’s hydration needs for preventive but also performance purposes.

Let’s start from the basics: in a sedentary subject the daily water change is about 2.5 liters (between inputs and outputs), but the liquids that actually circulate in the entire digestive system amount to approximately 9 liters. When it comes to athletes these quantities vary considerably and the demands for liquids are increased, obviously due to an increase in outputs, especially in the form of sweat. These losses must be adequately compensated by an increase in revenues, in order not to risk running into problems and repercussions (which we will discuss later).

The quantity of water to be reintegrated then varies according to the individual characteristics, the intensity and quantity of muscular work and, above all, in relation to the climatic conditions. It is therefore not possible to establish a priori the needs of the individual subject, which are strictly personal.

Physiology and mechanisms of the state of hydration

However, it is important to always keep in mind some physiological aspects, which allow us to better understand how the individual’s state of hydration works: body water represents about 60% of the total body weight in an adult man (therefore more than half the number we see on the scales when we weigh ourselves). The amount of intracellular water (also technically called ICW – Intra Cellular Water ) amounts to 2/3 of the total body water (66%), while the content of extracellular water (which is instead indicated as ECW – Extra Cellular Water ) amounts to 1/3 of the total body water (or Total Body Water – TBW ) and represents 35%.

Broadly speaking, the water requirement of a person who performs physical activity is about 1 ml for each calorie of energy expenditure . If physical activity exceeds 2 hours, dehydration can reach up to 5% of body weight: a value that is definitely too high to be underestimated, and which can also lead to serious complications if not promptly reintegrated. This lack of liquids must therefore be adequately and promptly rebalanced; otherwise it creates the conditions for a rapid deterioration in the athlete’s performance.

Compliance with the choice of hypo- or iso-tonic solutions and the use of any targeted integration is necessary to avoid that a significant amount of pure water also leads to the dilution of extracellular liquids. This could in fact determine, thanks to the action of the pituitary gland, the incretion (ie the production and secretion) of adiurethin, a hormone also known as “vasopressin”, with consequent elimination of excess fluids, but which also entails unpleasant consequences for a athlete.

In general, the lack of liquids and consequently of salts, especially in humid heat conditions, is signaled by symptoms such as nausea, vomiting, dizziness and general fatigue, as well as by a significant impairment of performance . If you insist, continuing in the activity despite the appearance of symptoms, muscle cramps and difficulty concentrating may occur. To correctly calculate the quantity of substances to be reintegrated, it is necessary to remember some concepts, related to the definition of osmolarity, which we report below.

The term Osmolarity means a physical quantity that measures the concentration of the solutions, and its value expresses the concentration of the solution under examination. Under normal conditions, the osmolarity is identical for all the fluids present in the various compartments of the organism (which can be divided into intra and extra cellular) The volume of extracellular fluid is generally estimated at 0.255 l / kg of body weight , and the factor main regulating the distribution of body water between the extracellular (EC) and intracellular (IC) districts is the osmotic pressureliquids themselves. Osmotic pressure is defined as that pressure that exactly balances the movement of the solvent generated by the difference in solute concentration between 2 concentrations. In the extracellular water compartment sodium is more important, while in the intracellular one potassium prevails .

The importance of a correct interpretation of osmolarity becomes fundamental in the preparation of a solution that must reintegrate energies and mineral salts in the athlete . First of all, you need to identify the goal, that is, if you are aiming for a quick replenishment of the water or if you want a quick energy supply, which can be used quickly by the body.

Integration of mineral salts

On an integrative level, two well-known minerals certainly play a fundamental role: magnesium potassium . Magnesium helps to support the physiological muscle function, contributes to the reduction of the feeling of tiredness and fatigue, supports the energy metabolism and contributes to the normal functioning of the nervous system. Potassium helps to support physiological muscle function, promotes the maintenance of normal blood pressure and also contributes to the functioning of the nervous system. In some situations, sodium supplementation may also be necessary, when with the Energy alone (generally sufficient) it was not possible to cover the increased needs or as a result of extreme sweating not followed by adequate recovery. Sodium, in fact, participates in the transmission of the nerve impulse, regulates the permeability of the membranes and contributes to the maintenance of water balance.

As regards the concentration levels of the solutions, these can be divided into Isotonic and Hypertonic , based on the time of assimilation by the intestine. An isotonic solution (with osmotic pressure equal to that of plasma) also guarantees a fast transit in the stomach, just slower than that of pure water.

A hypertonic solution, on the other hand, that is, with an osmotic pressure higher than that of the plasma, remains longer in the stomach and, once it reaches the intestinal lumen due to the high osmolarity, draws a considerable amount of liquids from the mucosa (theft of water) . This subtraction of water damages the entire organism, worsening a possible state of dehydration, causing diarrhea and, in any case, limiting athletic performance.

At the beginning of physical exercise, water is transferred from the blood plasma (ECW) to the interstitial and intracellular spaces: the metabolites begin to accumulate in and around the muscle Fibre; the osmotic pressure at these sites is increasing and attracts water. By increasing muscle activity, a rise in blood pressure is obtained, with a “extravasation” of water from the vascular compartment, often associated with an increase in sweating: essentially, from all these effects due to the increase in physical activity, muscles acquire water at the expense of plasma volume.

On the other hand, the reduction in plasma volume results in:

• Reduction in blood pressure;
• Reduced blood flow to the epidermis;
• Reduced blood flow to the muscles.

Risks of dehydration

Even a modest dehydration (equal to 1% of body weight), caused by sweating during exercise, can increase cardiovascular work by increasing the HR (heart rate) and thus reducing the body’s ability to thermoregulate.

Excessive sweating and / or urinary urination could also be a consequence of the large loss of electrolytes, which could lead to the development of serious repercussions, such as cardiac dysarrhythmias. All this even though Costill, a famous scholar of sports physiology, observed that the uniform loss of electrolytes, although considerable, mainly derived from the ECW compartment, and therefore the loss of ions through sweating and urination would result in small effects on the ion content. K + in the muscle cell.

Not to be overlooked is the influence of dehydration on our immune defenses. This effect, also known as the “open window effect”, derives from the fact that after exercise the immune system is committed to healing the micro-lesions of the muscles and cells, formed as a result of training. This is why, along with hydration, during and after performance, an athlete must remember to also keep the intestines protected. In fact, his entire health is at stake: so that the intestine is less “permeable” to attack by pathogens, supplements such as zinc and Vitamin C perform an excellent antioxidant action to protect cells from oxidative stress induced by intense physical activity, and thus supporting the physiological defenses of

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Dr. Massimiliano Febbi PhD