A full liquid saturation provides optimal physiological responses and good indices. Athletes who join the competition in a dehydrated state are at a disadvantage. For example, in the Armstrong et al. Athletes performed running at 5000 m (about 19 min) and 10 000 m (about 40 min) under conditions of normal hydration and dehydration. When dehydrated by approximately 2% of body weight (with the help of a diuretic before the load), the running speed decreased significantly (by 6-7%) in both cases. In a hot climate, dehydration worsens the performance even more.
For guaranteed adequate hydration, ACSM recommends that athletes use a nutritionally balanced diet and adequate beverages for 24 hours before the event, especially during food intake prior to loading, to stimulate the necessary hydration prior to training or competition.
If people live in a hot climate, free fluid intake is often not enough to meet the need for it. This is verified by research conducted with Puerto Rican football players. For the athletes observed for 2 weeks of training. When they were allowed to drink during the day for as long as they want (average consumption is 2.7 liters per day), the total amount of water in their bodies by the end of the first week was 1.1 liters less than with the mandatory consumption of liquid 4, 6 liters per day. In other words, free fluid intake did not compensate for its loss and made athletes start training or competitions already dehydrated.
Approximately 2 hours before exercise, it is recommended to consume about 500 ml (about 17 ounces) of liquid, which contributes to adequate hydration of the body and provides time for the allocation of excess water.
Indeed, subjects who consumed fluid 1 h before the load had a lower internal body temperature and heart rate than when they did not consume liquid.
Observations of color and volume of urine are for physically active persons an important practical means of assessing their hydration. The dark color of urine and its relatively small volume indicate dehydration, are a signal for consuming more liquid before loading. Monitoring the volume of urine is a common recommendation for mining workers who are constantly in high temperature and humidity conditions.
It is suggested that a solution of glycerol taken before the load in the heat can provide benefits for the cardiovascular and thermoregulatory systems. Hyperhydration caused by the consumption of glycerin, is accompanied by an increase in body weight, which is proportional to the amount of water retention (usually 0.5-1.0 kg). The fluid retention occurs because the molecules of glycerin after its absorption and distribution in the body fluid (with the exception of the watery moisture and cerebrospinal sections) provoke a temporary increase in osmotic pressure, contributing to a temporary decrease in urine formation. As in the following hours the molecules of glycerin are removed from the body fluid, the osmotic capacity of the plasma decreases, the urination increases and excess water is released.
There are a number of reasons why it is unreasonable to recommend athletes the hydration caused by glycerin.
- Athletes carry metabolic costs for excess body weight.
- There is no conclusive evidence that the hyperhydration induced by glycerin is physiologically useful.
- The side effects of glycerol absorption fluctuate between mild signs of bloating and dizziness and more serious symptoms - headache, dizziness and nausea.
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