The impact of dehydration on performance
Of all the concerns of an athlete, hydration is often the most neglected; and yet, it is without a doubt one of the most important determinants of the athlete's performance: dehydration can seriously affect performance and especially health.
The subject is crucial and yet even some experienced athletes tend to overlook it. This may be what explains the sudden tiredness felt halfway through. Understand that if you lose even 1% of your sweaty body mass during the effort, your performance is already decreasing by 2% on average.
Dehydration and hyponatremia
So why is hydration so important during exercise? It's very simple: water is essential to allow the good (fast and easy) circulation of blood, blood which itself carries oxygen and sodium to our muscles and allows each of our members to function efficiently. When you are dehydrated, your blood becomes thicker, so it circulates with less ease: your heart must pump harder. Drinking regularly during the race helps to compensate for fluid loss due to sweat so as not to lead to a dehydration situation.
Before going into the opposite excess, it is worth remembering one constant in sports nutrition: the challenge is to maintain a subtle balance. So if it is possible to be dehydrated it is also possible to drink too much: this is hyponatremia. It is a trap in which beginners often fall, following the advice of more adept runners who sweat much more and therefore need a more substantial fluid intake.
It must also be kept in mind that we are not all equal when it comes to sweat, our hydration needs are therefore simply not comparable and exportable from one runner to another based on his simple pace. Height, weight and gender, among others, affect the amount of sweat generated. As often, there is no magic formula; you have to get to know yourself, gradually discover yourself by trying and failing. Stay tuned to your level of hydrationThis can make the difference between a session where you are comfortable and feel good about a session where you have to provide a much larger effort than you should.
Find the happy medium
To guard against hyponatremia or excessive hydration, the isotonic drinks containing sodium may be preferred over plain water. Indeed, if the sweat is composed mainly of water, it also contains minerals, lactate and urea. This is the main contribution of isotonic drinks: not only do they help you maintain proper hydration, they also compensate for all non-water losses caused by sweat.
Indeed, when you are in excessive hydration, the sodium level is low and your blood volume is decreased ; as a result, an antidiuretic hormone (ADH) is produced and retains water in your body. Which lowers the sodium level again by diluting the blood ... A vicious circle that must be avoided at all costs.
Excessive hydration is actually more dangerous than dehydration: it can be fatal. Thus, if there is no good practice that we could advise everyone, there is nevertheless this advice which can be universal: stay sensitive to your level of hydration during the effort ; finding the right balance is something that is gradually being done as you accumulate the racing experiences.
In summary: the little advice
On this point, you have to force yourself to drink well before, during and after exercise but also on non-sport days at least 1,5 to 2 liters.
Relative to intestinal camps, this point can be important because if the sugars and water are not assimilated they stagnate and "ferment" in shooting intestines and voila .... cramps.