Despite the commonly known importance of water in our bodies, many athletes do not seriously consider the effects of hydration during and after athletic performance.

Water maintains blood volume, regulates body temperature and is involved in muscle contractions (1). Perspiring is regulated by the autonomic nervous system and is controlled unconsciously by the hypothalamus; the structure in the brain that regulates the body’s status quo. Sweating is the body’s primary way of maintaining optimal body temperature (1). Consuming liquids replenishes the fluids lost during exercise. Restoring fluids maintains normal muscle function, helps prevent a decrease in physical performance and reduces the risk of heat stress (1). The symptoms of exertional heat stress are tachycardia, hypotension, hyperventilation, vomiting, diarrhea, seizures and coma (4). Despite these serious effects, many athletes do not seriously consider the effects of hydration on athletic performance.

A loss of sweat equal to 2% of body weight causes a noticeable decrease of physical and mental performance.  Losses of 5% or more of body weight during physical activities may decrease the capacity for work by roughly 30% (6). In addition to dehydration affecting the capacity for work, losses of perspiration greater than 2% of body weight increases the risk of nausea, diarrhea, vomiting and gastrointestinal problems (1).

Dehydration may cause a reduction in blood volume, decreased skin blood flow, decreased sweat rate, decreased heat dissipation, increased core temperature and an increased rate of glycogen use. The most likely physiological mechanism affecting a person’s maximal aerobic power (VO2 max) and hence athletic performance is one’s maximal cardiac output (2). As dehydration reduces plasma volume and therefore increases blood viscosity, central venous pressure decreases and reduces the amount of blood returning to the heart. During peak athletic intensity, these changes can decrease the amount of blood entering the heart during diastole; the phase in the cardiac cycle where the heart relaxes and fills with blood. Less blood entering the heart during diastole decreases the amount of blood that may possibly leave the heart during systole, the phase where the heart contracts, consequently decreasing cardiac output (2).

An increased core temperature during a dehydrated state is accompanied by a larger aromatic amine response, possibly leading to an increased rate of glycogen breakdown in muscles. An increased rate of glycogen breakdown may contribute to an increased level of fatigue in the muscles used during the athletic activity (2). The breakdown of glycogen during exercise leads to an intracellular increase of acids, principally lactic acid. As lactic acid is produced by the breakdown of glycogen, pH decreases causing skeletal muscle fatigue (5).

Moreover to skeletal muscle fatigue, research from the University of Connecticut tested athletes’ muscle growth during resistance training over a period of three different states: Euhydrated, moderately dehydrated (2.5% of body weight) and critically dehydrated (5% of body weight). Researchers drew the athletes’ blood and examined certain molecules directly correlated to muscle growth. The athletes in a dehydrated state had an increased level of cortisol, which competes for certain enzymatic receptors in the body reducing the level of testosterone, the primary hormone required for muscle growth. Additionally, increased cortisol concentration reduces the amount of testosterone released as a response to resistance-specific weight training (3).

Studies on water intake are limited in data compared to intake of other nutrients. There is no ideal amount of water that should be consumed. Despite the lacking data, the Institute of Medicine has declared an estimated ideal volume of water that people should consumed daily. Male adults above the age of 18 should consume about 4 litres. Females above the age of 18 should drink about 3 litres of water.

Water is involved in the majority of chemical reactions involved in athletic performance. It is important that athletes are hydrated before, during and after physical activity to achieve their maximal physical performance.



1. “Fluids and Electrolytes.” SpringerReference (2011): n. pag. June 2009. Web. 22 June 2015.

2. Jeukendrup, Asker E., and Michael Gleeson. Sport Nutrition: An Introduction to Energy Production and Performance. Champaign, IL: Human Kinetics, 2010. N. pag. Print.

3. Brown, Jordana. “” Weider Publications, n.d. Web. 22 June 2015.

4. Binkley, Helen M. et al. “National Athletic Trainers’ Association Position Statement: Exertional Heat Illnesses.” Journal of Athletic Training 37.3 (2002): 329–343. Print.

5. Westerblad, Håkan, David G. Allen, and Jan Lännergren. “Muscle Fatigue: Lactic Acid or Inorganic Phosphate the Major Cause?” American Journal of Physiology 17.1 (2002): 17-21. Web. 10 July 2015.

6. Jeukendrup, Asker, and Michael Gleeson. “Dehydration and Its Effects on Performance.” Humankinetics. N.p., n.d. Web. 29 July 2015.