How and when is it useful to use hydrosaline drinks?

By Dr. Francesca Fanolla

Now present as market products available in various flavors, colors, various brands, etc., hydrosaline drinks have become quite "fashionable" among the regular and occasional gym goers, occasional sportsmen and even people who use them as the " water, Coca Cola or beer ...
But not everyone knows that these drinks, certainly much "healthier" than the aforementioned Coca-Cola and the alcoholic beer, have specific characteristics relating to the purpose for which they were invented and produced.
Before talking about them I make a premise on SWEAT, closely related to the use of hydrosaline supplements in aerobic activities or which in any case involve abundant sweating.

SWEAT is produced by the sweat glands, scattered a little along the entire body surface, and is made up of WATER and SOLUTES (mainly sodium, potassium, magnesium, chlorine among the electrolytes and in addition by lactic acid and urea).
The concentration of electrolytes in sweat varies with the rate of secretion of the sweat glands. As the speed of glandular secretion increases, the concentration of sodium (Na) and chlorine (Cl) in sweat also increases, while the concentration of magnesium (Mg) and potassium (K) tends to decrease. Sodium and chlorine are therefore the two electrolytes which are lost most after a "profuse sweating.

During physical activity, practitioners must aim to replenish the water and mineral salts lost through a calibrated supply of different elements. This reintegration becomes absolutely necessary when the water loss with sweating reaches 2.5 / 3 liters, an easily reachable threshold in endurance sports. For example, during races such as the marathon, the amount of sweat produced can reach 4/6 liters equal to 10-15% of the total body water.
The average water loss was however calculated in 1.25 l / h of activity but the water intake to prevent dehydration is about 0.5 l / h of activity.
Sweat is a HYPOOSMOTIC LIQUID, that is a body liquid with an OSMOLARITY (concentration of particles present in solution, or solutes) lower than that of all other body fluids; in fact, sweat has a concentration of 80-180 mOsm / l compared to 290-300 mOsm / l of the plasma.
Sweating therefore always leads to a loss of water in excess of the loss of salts.
If the intake of WATER does not increase in parallel with the loss of sweat, the hydro-saline balance is said to be NEGATIVE. This results in a reduction in the volume of body fluids and in the amount of sodium in the body, associated with an increase in the concentration of solutes osmotically active (osmolality).
It is therefore wrong to use HYDROSALINE DRINKS during an activity that does not involve excessive sweat loss (such as the weight room or a low intensity aerobics class).
The rational reintegration of water and salts is represented by less concentrated drinks than plasma (hypotonic), which therefore are closer to the osmolarity of sweat. Therefore, using a hypotonic drink does not alter the physiological mechanism of sweating.

It is therefore always advisable to increase the water intake when you have intense sweating. In particular, the intake of liquids before and during muscle work reduces and delays the onset of dehydration and its consequences.
In any case, it is essential to reintegrate the water lost at the end of the exercise.
Conversely, the reintegration of salts is appropriate, in general ONLY if the sweat losses are very important (such as during a spinning class, a cross-country style run, high intensity fitness classes with aerobic regime or cardio fitness). In this case, in fact, the quantity of salts lost by the body can amount to many grams, resulting equal to or greater than the daily intake.

It is important to underline that in the calculation of the concentration (osmolar load) of any liquid also sugars are important. In the drinks commonly on the market the sugars contained represent the greatest osmolar load, clearly higher than that of salts. This fact can have two negative aspects. :

  1. slow down gastric emptying, causing a delay in the actual absorption of the drink.
  2. cause a recall of water from the blood to the intestinal lumen, obtaining the opposite effect to that desired, as the blood will concentrate further.

If the plasma is too concentrated with respect to sweat, fluid retention occurs instead of a physiological loss in sweat with a consequent decrease in heat dispersion (hyperthermia).
The depletion of the body's hydrosaline reserves and energy reserves during prolonged physical exercise is the main consequence of the progressive decline in athletic performance and any damage caused by hyperthermia (heat stroke).
It is therefore advisable, during and after intense physical exercise, to consume an adequate amount of fluids, taking into account the following warnings:

The reintegration must take place on the basis of the actual loss of liquids. It must therefore be customized on the climatic conditions.

Reintegration should preferably take place after physical exertion. In all those endurance sports in which physical effort exceeds 60 minutes in duration, reintegration can also take place during, possibly in fractional administrations.

The reintegration will be favored by the intake of fresh drinks (10-15 °) which are able to contribute to the control of hyperthermia and to accelerate gastric emptying.

The best reintegration is obtained by taking drinks with a low concentration of dissolved salts and sugars (hypotonic) since, as we have seen, sweat is hypotonic compared to plasma.

What do saline supplements do:

Hypertonic supplements: these are drinks whose concentration, consisting of carbohydrates and mineral salts, determines an osmotic pressure, that is an "attraction of liquids, higher than that of plasma. They require very long times of assimilation in the intestine.

Isotonic supplements: these are drinks whose concentration determines an osmotic pressure equal to that of plasma. They require average assimilation times in the intestine.

Hypotonic supplements: these are drinks whose concentration determines an osmotic pressure lower than that of plasma. They are the drinks that require the shortest time of assimilation in the intestine.

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