Hydration in Sport

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Craig Finn Foundation Degree Nutrition Assignment – Hydration Nov 2012

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...
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