Hydration in Sport

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Hydration in Sport

Boxing is a sport renowned for it’s propensity for dehydration in “making weight”. This document is written as an informative aid for boxers and coaches and discusses the impact of hydration and dehydration on physiology and performance. Although written with boxing in mind it has equal relevance to the wider sporting community. Hydration is the process by which water is ingested and absorbed into the body and the term euhydration synonymous with describing normal body water content (Wenhold, and Faber 2009). Water is the most abundant substance in the human body and vital to overall health and wellbeing.

The muscles comprise over 70% water, as does the brain, blood plasma is 92% water and even bones consist of over 22% water. Water is essential in maintaining body temperature and blood volume, digestion for absorption/excretion and has a major impact on physical performance. Hydration studies demonstrate positive proof that a precise ratio of protein and carbohydrates promotes cellular rehydration and supports muscle recovery (Kalaman and Lepely 2010).The sports supplement industry is driving current research in this area of hydration, with (http://thorne-performance.tumblr.com 2009) stating:

“Water is absorbed relatively slowly however, this type of hydration is really only extracellular (fluid outside the cell and collectively equates to 20% of the body’s water). Intracellular fluid inside the cell represents 40% of body weight and equates to 70% of the body’s water. True cellular hydration (intracellular) for sports performance is far more complicated than drinking water or a “sports hydration beverage” that is simply electrolytes and carbohydrate. Drinking water will improve your overall hydration status, but it will not significantly alter the ratio of intracellular to extracellular fluid”.

Electrolytes help regulate the distribution of water throughout the body and are required for nerve conduction and muscle contraction. The major electrolytes are sodium, potassium, chloride and magnesium. Electrolytes are lost as the athlete sweats but there is an adaptive response to this; as a boxer acclimatises over multiple training sessions to their environment, and increases his or her fitness, there is a decrease in the amount of water and electrolytes lost during exercise. Adding electrolytes to the fluids a boxer drinks can decrease urine output and help the fluids empty more rapidly from the stomach to become available for tissue hydration (Douglas et al 2000). Hyperhydration refers to an increase in body fluid above the euhydrated state. This can be achieved by ingesting excess water, often combined with glycerol which has a “sponge like” effect and aids water retention. The current scientific consensus however is that hyperhydration does not provide a meaningful physiological or performance advantage over simply remaining well hydrated during exercise (Murray 2007).

The contribution of food to hydration levels is something that is often overlooked, numerous studies reveal that between 20% – 25% of total fluid intake comes from food, (fruit and vegetables having a high water content). Food intake also assists hydration through water binding to the carbohydrate content to form glycogen (1 part carbohydrate: 3 parts water). Dehydration refers to the process of uncompensated water loss via urine, sweat, feces, and respiration and is defined as a dynamic loss of body water or transition from euhydration to hypohydration (Armstrong 2007). During most sports, more fluid is lost (via sweating and breathing) than can be replaced (by drinking), and some degree of dehydration is therefore inevitable in sport. Dehydration provokes changes in cardiovascular, thermoregulatory, metabolic, and central nervous function that increase as dehydration worsens.

Dehydration of 1% – 2% of body weight begins to compromise physiologic function and negatively influences performance. Dehydration of >3% of body weight further disturbs physiologic function and increases an athlete’s risk of developing a heat illness (Murray 2007). Taken to the extreme, rapid weight loss when achieved through dehydration can be fatal. Excessive dehydration can harm bodily functions, leading to kidney failure, heat stroke or heart attack, indeed in 1997 three young American wrestlers tragically died whilst trying to “make their weight” (Viscardi,1998).There is increasing evidence that even small levels of dehydration can negatively affect exercise performance. This is reflected in a 2005 scientific consensus statement issued by the American College of Sports Medicine: “Dehydration of >2% of body mass can compromise physiological function and impair exercise performance capacity”.

Measuring Hydration. The best approach involves comparing 2 or more hydration indicators as single measurements lack accuracy. Cheuvront et al 2005 describes the following indicators as requiring minimal technical proficiency and can be used easily to evaluate hydration status during training: Body Weight Difference. The change of body weight represents a straightforward, effective assessment of hydration status and is especially appropriate for measuring dehydration that occurs over a period of 1 – 4 hours, (very simply, body weight lost during activity = sweat loss). Urine. If kidney function is normal, urine is concentrated and output is low when the body is dehydrated. When a temporary excess of body water exists, urine is dilute and plentiful. This offers 3 options to evaluate human hydration status using urine: 24 Hour Urine Volume. Urine volume can be used as an indicator of hydration status.

Urine output varies inversely with body hydration status, urine output generally averaging 1 – 2 litres per day, but can reach 20 litres per day in those consuming large quantities of fluid. The minimum urine output is approximately 500 ml per day, although for dehydrated subjects living in hot weather, minimum daily urine outputs can be less. Physical activity and climate affect urine output. Exercise and heat strain will reduce urine output by 20% – 60%, while cold and hypoxia will increase urine output. Urine Specific Gravity. The density (mass per volume) of a urine sample relative to water can be measured using a handheld refractometer. Any fluid that is denser than water has a specific gravity greater than 1.000. Normal urine specimens usually range from 1.013 – 1.029 in healthy adults. When serious dehydration or hypohydration exists, urine specific gravity exceeds 1.030 Conversely, excess water consumption show values range from 1.001 – 1.012.

Urine Color. A numbered scale has been developed that includes colors ranging from very pale yellow (1) to brownish green (8). Urine color does not offer the same precision and accuracy as urine specific gravity but provides a useful estimate of hydration state during everyday activities. Note that vitamin supplements can drastically alter the colour of urine via the excretion of excess water soluble vitamins. Thirst. As a physiological response to dehydration, thirst is a reliable indicator of 1% – 2% dehydration. Although thirst offers an estimate of mild dehydration, it better serves to remind individuals to drink more fluids as dehydration has already occurred by the time the thirst mechanism functions.


Hyponatremia (water intoxication) is a disorder in fluid-electrolyte balance that results in an abnormally low plasma sodium concentration. A sustained decrease in plasma sodium concentration disrupts the dynamics of water exchange across the blood-brain barrier, resulting in a rapid influx of water into the brain. This can cause swelling in the brain, leading to a series of increasingly severe responses, such as confusion, seizure, coma & even death. Hyponatraemia in athletes is often, although not always, caused by excessive drinking. During exercise, urine production is decreased, reducing the body’s ability to excrete excess water, while at the same time sodium losses are increased through sweating. The combined effect makes it much more likely that the body’s sodium content will be significantly diluted.

Hypernatremia is defined by the Oxford Dictionary of Sports Science & Medicine as “The presence of an abnormally high sodium concentration in the blood plasma. It may occur as a result of excessive sweating and inadequate fluid intake”. Hypernatremia is generally not caused by an excess of sodium, but rather by a relative deficit of free water in the body. For this reason, hypernatremia is often synonymous with the less precise term, dehydration. Re-hydration. After weigh-in, fighters typically try to replace lost body fluids in an attempt to return to a normal state of hydration. However, the fighter is unlikely to eat and drink sufficiently because of the negative effects of fighting on a full stomach. Also the time between weigh-in and fight is usually insufficient for fluid and electrolyte balance to be fully restored, or for rehydration and replenishment of muscle and liver glycogen (ACSM, 1996; Yankanich et al)

This is supported by Foster (1995, p.66) who identified that “The body takes from 4 – 48 hours to fully recover from moderate dehydration, meaning there isn’t enough time between weigh-in and the match to ensure peak performance and health.” Effect of Ambient Temperature. The impact of dehydration on performance is less under cooler environmental conditions than under hot conditions and exercise in heat itself, even with no dehydration, impairs performance .(Sawka & Pandolf, 1990).

Although the majority of scientific evidence illustrates that dehydration impairs physical performance, exercise in cold weather (Cheuvront et al) showed that dehydration (<3% bodyweight) impaired exercise performance in a temperate environment, but not in a cold environment. The higher cardiac output and lower core temperature during exercise in the cold may explain why dehydration has less of an effect on performance. The relationship between literature (Journals/books etc) and the effects of dehydration on sporting performance


Dehydration does have something going for it: it enables boxers to compete below their natural weight. A study involving former British lightweight champion Derry Matthews noted a 10 per cent increase in measures of strength and power were obtained by using acute dehydration strategies to make weight when followed by an aggressive rehydration strategy). This approach enabled Mathews to preserve 2kg more of lean mass during a 12 week training camp than was previously achieved when pursuing a strategy with greater hydration.


Pre-fight Weight:
Urine colour analysis:
During Fight: Water sipped between rounds (3 min intervals)
Post-fight weight:
Urine colour analysis:
Ref below : Peak Performance Special Issue, hydration, Number 212

Prevention: Continue to sip water

Prescription: Drink 500ml for every kg bodyweight lost


The results of many decades of research make it clear that dehydration often impairs physical performance and drinking sufficient volumes of fluid during physical activity to minimize dehydration is arguably the simplest and most effective means of sustaining physiological function and improving physical performance. • Dehydration during physical activity is commonplace because voluntary fluid intake is often less than fluid loss through sweating. • Dehydration results in unavoidable, negative effects on physiological function and exercise performance. The magnitude of the effects of dehydration is exacerbated by increases in heat stress, exercise duration, and exercise intensity. • Adequate drinking during exercise helps attenuate the reductions in blood volume, cardiac output, muscle blood flow, skin blood flow, the rise in core temperature, and the impairment in exercise performance that accompany dehydration. • If boxers are to continue dehydrating to make weight for fights, then they should ensure they use an aggressive re-hydration strategy to supplement this practice and simple self assessment of hydration is essential to maintain health and performance.


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5. Murray B. October2007. Hydration and Physical Performance. Journal of The
American College of Nutrition, Vol 26, No5, 542S-548S 6. Assessing Hydration Status: The Elusive Gold Standard
Lawrence E. Armstrong, PhD, FACSM Journal of the American College Of Nutrition J Am Coll Nutr October 2007 vol. 26 no. suppl 5 575S-584S

7. Godek, Sandra Fowkes., Bartolozzi, Arthur R., Burkholder, Richard, Sugarman, Eric, & Dorshimer, Gary. (2006). Core temperature and percentage of dehydration in professional Linemen and backs during preseason practice. Journal of Athletic Training, 41(1)8-17.

8. Decker, Meredith. The Effects of Hydration on Athletic Performance, Underground Research Journal for the Human Sciences June 2011.

9. Douglas J. Casa, PhD, ATC, FACSM*, Priscilla M. Clarkson, PhD, FACSM, and William O. Roberts, MD, FACSM. American College of Sports Medicine Roundtable on Hydration and Physical Activity: Consensus Statements. December 2005. 10. Mike Viscardi, Weight Issues In Wrestling. http://www.vanderbilt.edu/AnS/psychology/health_psychology/Weight-Wrestling.htm 11. Urine colour analysis chart, http://drdietright.com/my-blog/water-for-weight-loss/

12. Samuel N. Cheuvront, Ph.D., Michael N. Sawka, Ph.D. FACSM, Sports Science Exchange 97 VOLUME 18 (2005) NUMBER 2, SUPPLEMENT, Hydration Assessment of Athletes

13. Kathryn M. Kolasa, PhD, RD, LDN Carolyn J. Lackey, PhD
Ann C. Grandjean, EdD, FACSM, Hydration and Health Promotion – an overview of the 2006 International Life Sciences Institute North America Technical Committee on Hydration organized a conference on hydration and health promotion. 2006.

14. http://www.gssiweb.com/Article_Detail.aspx?articleid=706&level=2&topic=1

15. Michael Kent,The Oxford Dictionary of Sports Science & Medicine.


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