Water, being the largest component of the body, makes up 40 – 70% of our body mass. This amount of water varies from person to person, depending on age, gender, and body composition. Water comprises about 65 – 75% of the weight in muscle and approximately 10% of the weight in fat mass. So, for individuals of similar body mass, the one with more muscle mass and lesser body fat will contain more water than those with the opposite body composition.
The importance of water cannot be overlooked as it is vital for the transportation of nutrients and gases, removal of waste products, lubricates joints, cushions our organs (heart, lungs, intestines, and eyes), regulates body temperature and maintaining fluid balance (11). There are 2 areas in the body where water is contained, inside the cells (intracellular) and outside the cells (extracellular). About two-thirds of the total body water comes from intracellular sources and the remaining from extracellular sources. Approximately 20% of the extracellular water travels around your body as blood plasma (liquid portion of blood) to maintain the blood volume and to allow blood circulation (18). Therefore, having adequate hydration is essential for our body to function effectively (8).
“How is hydration critical for sports performance?”
Exercising intensively in a hot environment for a prolonged duration results in more significant water loss, aka dehydration (the process of losing water). Almost any dehydration compromises physiologic function and the body’s ability to maintain a stable temperature. Even under optimal temperature conditions, the body can only survive a few days without water (16).
Studies have shown that athletes losing water as little as 1 – 2% of their body mass can lead to reduced performance due to an increase in physiological stress (9, 12, 10, 19, 15). These include an elevation in heart rate, core temperature, muscle glycogen use and a decrease in cardiac output (amount of blood pumped throughout the body in a minute), cognitive awareness (attention, decision-making, judgment, etc.), anaerobic power, and time to fatigue (13, 12, 10, 19).
During exercise, our body loses water in the form of sweat and vapor (16, 22). To help regulate our core body temperature, the process of perspiration and evaporation provides a way to cool us down. As exercise intensity increases, our breathing rate goes up as well, losing water in the process as water droplets when we exhale. Most of the water lost through sweating comes from blood plasma, and this affects the blood volume. To keep up with the initial amount of blood volume circulated and to maintain the blood pressure, the blood vessels would constrict and become narrower (21), and the heart pumps harder and faster (17, 7). However, if dehydration continues, the blood pressure will eventually drop due to the decrease in blood volume. Even though the heart is working harder, it will not be sufficient to maintain the blood pressure due to the reduction in blood volume (7). Upon reaching this point, the blood pressure starts to fall directly in proportion to the amount of water lost (6).
Therefore, as water loss progresses, your circulatory capacity progressively decreases as well. Not only would this lead to a gradual deterioration in sports skill performance (power, strength, accuracy, endurance, etc.), it can also pose a risk to your health (14, 5).
Hydration and Health/ How dehydration impact health and performance
Electrolytes are essential minerals that are vital for the body to function normally. Some of the electrolytes include sodium, potassium, magnesium, calcium, and chloride. These electrolytes are important for muscle contraction and nerve conduction (1).
When our body loses water, we lost electrolytes as well. Any electrolyte imbalance in the body’s fluid could potentially cause a negative impact on health and performance. The most common imbalances are sodium and potassium. Sweat contains sodium, and exercising intensively for a prolonged period and hydrating excessively with only water or a no or low sodium beverage may dilute the blood sodium levels, potentially resulted in a condition called hyponatremia (4). When blood sodium levels reached a dangerously low level (below 130 mmol/L), intracellular swelling may occur. When it reached below 125 mmol/L, it can lead to headaches, nausea, vomiting, muscle cramps, swollen hands and feet, restlessness, and disorientation. A further drop in blood sodium levels to 120 mmol/L increases the risk of developing cerebral edema, seizures, coma, brain stem herniation, respiratory arrest, and even death (20, 2).
To avoid hyponatremia, we have to ensure our water intake not exceeding the amount of sweat lost. In other words, the individual should not weigh more than he or she did at the start of the exercise or training session. It is advisable to replenish water loss with either sports drinks or food that contains sodium. In addition to sodium, it would be good for rehydration to include potassium. Research shows that more than 97% of adults in the United States do not meet the dietary recommendations for potassium (3). Therefore, it is recommended to include foods/ drinks rich in potassium such as bananas, milk, potatoes, tomatoes, citrus fruits, and melons.
A general understanding of nutrition principles and applications is essential for any strength and conditioning professionals and coaches to provide sound guidelines to help athletes improve their diets. For athletes to reap maximal benefits from training, adequate hydration and electrolytes are just as important as having an appropriate amount of energy, macronutrients, vitamins, and minerals. If you're keen to know more about the strategies for preventing dehydration and the recommendation for fluid intake, check out this article.
References
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