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Intensive sport in summer: well hydrated for a good performanceIntensive sport in summer: well hydrated for a good performance
The arrival of the summer season with its hot spells is often a difficult period for sportsmen and women to manage. Water intake must be carefully controlled in order to avoid poor performances.
Several factors influence the body's water requirements. What are the water requirements of sportsmen and women? How do you recognize the signs of dehydration? In this section, out nutritionist gives you the answers.
Water represents 2/3 of a sportsman or woman's body
The human body contains more than 50% water. The proportion of water in the body varies throughout life :
- It decreases with age as a result of the loss of muscle volume. Thus, the body weight of a new born is 74% water at birth while it is around 59% for an adult man. Table 1.
- It is greater in thin people or those of normal build. Adipose tissue contains less water than muscles.
- Men have a greater body water content than women because the average fat volume is generally smaller.
Table 1. Percentage body weight of water in humans as a function of age and sex.
| Age | % eau / poids corporel |
|---|---|
| 0-6 months | 74 |
| 7-12 months | 60 |
| 1-12 years | 60 |
| 12-18 years M | 59 |
| 12-18 years W | 56 |
| 19-50 years M | 59 |
| 19-50 years W | 50 |
| 51 + years M | 56 |
| 51+ years W | 47 |
Source: Grandjean AC, Campbell SM. (2004). Hydration: Fluids for Life. ILSI North America. Monograph Series.
Water is essential for the body's metabolic functions :
Thermoregulation
Maintaining body temperature by absorbing heat and then releasing it by evaporation
Transport and excretory system
Transport of nutrients, hormones and enzymes in the blood and transport of oxygen to the cells. Excretion of waste products and toxins in the urine
Chemical reactions
Involved in numerous chemical reactions and in particular in glycolysis necessary for ATP production (adenosine triphosphate - energy used for muscular contraction).
Composition of joints and organs
Water take part in lubricating joints (synovial fluid) and organs of the digestive system (mucus and saliva). It makes up 75% of the weight of muscles.
Adequate hydration to improve physical and metal performance
It's vital for sportsmen and women to maintain a good level of hydration. Intake of water associated with regular training is key to sporting success. Losses of body water, which are nearly nothing at normal temperature in a sedentary individual, increase to 1.4 L in warm weather and can go as high as 5 L in sportsmen and women during prolonged exercise.The human body is made up of different systems in which water plays an important role in cellular renewal. This is why inputs (food, drink) must be equivalent to outputs (stools, breathing, sweat, urine) to provide all intra- and extra-cellular compartments in the body and avoid significant losses of essential vitamins and minerals (sodium, potassium, magnesium, zinc, vitamin C, etc.). Figure 1
Figure 1. Water intake and losses in adults at ambient temperature (expressed in ml / day). (Make a drawing of the human body)
[ schema à fournir ]
Source: Food science, Nutrition and Health, Ed BA Fox, AG Cameron, 6th edition, London: Edward Arnold 1995.
Several studies have shown that inadequate liquid intake rapidly leads to reduced performance. For prolonged exercise, dehydration acts especially on stamina while for shorter exertions it reduces the muscle strength needed for contraction.
Water intake also plays a role in maintaining cognitive functions (vigilance, concentration, short term memory, psychomotricity) and delays in the appearance of sensations of fatigue during exercise. This is all the more important given that several of numerous sports require both physical and intellectual abilities (tennis, basketball, orienteering, football, rugby, jumping, skiing, mountain biking, etc.).
A simple fall of 1% of body weight of water leads to the first signs of dehydration and has an influence on physical and intellectual performance. It is estimated that a loss of 2% reduces sporting ability by 20%. The first symptoms synonymous with dehydration are: thirst, clammy skin, headaches, loss of lucidity, cardiac palpitations and nausea. More severe dehydration can cause muscle and tendon problems, cramps and hyperthermia that can lead to cardiovascular problems, coma and even death.
Water requirements of sportsmen and women: how do you optimise intake ?
In sportsmen and women, water intake must be not only sufficient but regular. Drinks must be regularly spread throughout the day in order to compensate for losses. It is essential to drink before feeling thirsty! In fact, you cannot rely on the physiological thirst mechanism which provides a signal much too late and doesn't relate to real needs. When you feel thirsty, the body is already slightly dehydrated.Recommended daily water intakes have been defined by WHO. For each population, these must be adapted according to age, diet, level of physical activity, climate and state of health.
They are shown in table 2.
Table 2. WHO recommendations regarding water intake in adults (2003).
| Sex | Normal temperature (litres/day) | Hot climate or moderate physical activity (litres/day) |
|---|---|---|
| Women (average weight 58kg) | 2,2 | 4,5 |
| Men (average weight 70kg) | 2,9 | 4,5 |
Source : Howard G, Bartram J. Domestic Water Quantity, Service, Level and Health. World Health Organization, 2003.
How do you drink during training and in competition ?
During training as in competition, you must arrive well hydrated. It is essential to drink regularly during intensive sessions and when it's hot or very cold.To have good control of water intake, weigh yourself before and after exercise, and drink one litre of liquid for every kg lost. If you don't have a set of scales to hand, drink one litre of water per hour of intense exercise.
During exercise, the ability to absorb water in the intestine is reduced because the blood is more urgently needed to circulate in the heart, brain and muscles. This is why it is recommended to drink in small doses of 150 to 200 ml of liquid every quarter of an hour.
In a period of competition, the best hydration strategy starts the evening before and continues during the hours preceding the event. During exercise, isotonic energy drinks are useful because they contain the same concentrations of mineral salts and glucose as found in the blood, which enables better hydration and assimilation than for water. In addition, the enable rehydration while also recharging carbohydrate reserves and compensating for mineral losses. IsostarHydrate & Performisotonic exercise drink preparations contain carbohydrates but also sodium, potassium, magnesium and vitamin B1. Hydrate & Perform drinks can also be used as a waiting drink by diluting in a larger volume of water, when they become hypotonic.
And recovery?
After an intense training session of a competition, it is essential to thoroughly rehydrate yourself to rebuild your water reserves and help waste elimination. Isostar offers a varied range of isotonic exercise drinks to help recovery. Contrary to received ideas, moderate consumption of alcohol is recommended as well as diuretic drinks such as coffee or tea.
Click here to read our specialised advice on hydration.
Isostar nutritionist. July 2007