Serious athlete, or weekend trooper, proper hydration is crucial to health and sport performance (Maughan & Shirreffs, 2010; Oppliger et al., 2005) . Water is the main component of the human body and is accountable for around 45-70% of total body mass (Lanham-New et al., 2011). Body water can be split into two components: intracellular fluid (ICF) and extracellular fluid (ECF) (Ames & Nesbett, 1966; Oppliger & Bartok, 2002) . The ICF makes up two-thirds of the total body water (Oppliger & Bartok, 2002). The ECF can be subdivided into interstitial fluid (found between the cells) and the plasma which corresponds to around one-quarter of the ECF volume (Lanham-New et al., 2011). It is important to note that the water found in the body is not just plain water. It contains a variety of electrolytes (compounds that separate into ions when in solution) and solutes which range in concentrations (Starker et al., 1983). The main positively charged electrolytes (cations) in the body are sodium, potassium, calcium and magnesium (Lanham-New et al., 2011). Conversely, the main negatively charged electrolytes (anions) are chloride and bicarbonate (Lanham-New et al., 2011). The location of these electrolytes varies through the body’s water compartments. In the ECF, sodium is the core electrolyte, whereas potassium is existent in a lower concentration (Lanham-New et al., 2011). In contrast, in the ICF potassium is the main electrolyte and sodium concentrations a lot lower (Lanham-New et al., 2011). It is important for the body to keep this distribution of electrolytes as this allows the body’s cells to function properly and allows the body to communicate with itself (Murray, 2007). This does not happen when a person becomes dehydrated.
The main ways the body loses water is from the urinary system, the skin, the gastrointestinal tract and the respiratory surfaces. The loss of water in the body will come from both the ICF and the ECF compartments.
People sweat during exercise in order to assist the body in controlling core temperature (McDermott et al., 2000). As a result of sweating the body loses fluid. The rate at which the body loses fluid through the sweat response is dependent on a range of variables including exercise intensity, environmental conditions, clothing and baseline hydration status (Maughan & Shirreffs, 2010). Once an athlete sweat loss exceeds fluid intake, they become dehydrated. Dehydration of 1%-2% of body weight is detrimental to physiological function and negatively affects performance (McDermott et al., 2000). Dehydration of 3% of body weight increases a player’s risk of developing an exertional heat illness like heat stroke or heat exhaustion. Dehydration associated injuries include fatigue, cramps, heat exhaustion and heat stroke (Casa et al., 2005). Appropriate hydration is important in an athlete’s ability to perform (Oppliger et al., 2005).
Team sports like rugby, consist of prolonged periods of exercise with repeated intermittent high-intensity bursts combined with lower intensity exercise (Chiwaridzo et al., 2017). Fatigue resistance and cognitive function (important for decision making and for the execution of complex skill) is needed for performing at the top of the game in rugby (Lanham-New et al., 2011). As mentioned above, dehydration can impair a players cognitive and physical ability and therefore is important to stay hydrated in order to improve performance (Maughan & Shirreffs, 2010). Many protocols have been researched and developed to attempt to investigate the effect of hydration status may have on sports performance.
Hyper hydration (drinking an excess of fluid) is an investigated topic (Shirreffs, 2003). In a healthy player, the kidneys should dispose of any excess body water, thus drinking an excessive amount of water before exercise is ineffective (Murray, 2007). The American College of Sports Medicine recommends individuals slowly drinking a moderate amount of fluid (5-7ml/kg) at least four hours before exercise in order to boost hydration (Casa et al., 2005). If the player does not produce urine or the urine is dark and highly concentrated, more fluids (3-5ml/kg) should be ingested slowly around two hours before exercise (Lanham-New et al., 2011). The guidelines also state that consuming drinks that contain sodium or food containing sodium can help to encourage thirst and preserve the consumed fluids (McDermott et al., 2000).
Hydration during exercise
As mentioned above, the intermittent nature of rugby permits players to have access to fluid intake during competition when compared to other sports (Lanham-New et al., 2011). Variables such as exercise intensity, frequency, duration and environmental factors make providing specific protocol for hydrating during exercise near enough impossible and not sensible (Lanham-New et al., 2011). The American College of Sports Medicine state the goal during exercise should be to inhibit excessive body mass loss (>2%) in order to prevent any excessive changes in electrolyte balance (Casa et al., 2005). By doing so, this should minimise any compromises in performance due to fluid levels. Due to variability in sweating rates and sweat electrolyte content between individuals, custom fluid replacement protocols (like above) should be used instead of one protocol for everyone (Murray, 2007). This is possible by measuring body mass before and after exercise to estimate sweat rates (Oppliger & Bartok, 2002).
Plain water is not the perfect post-exercise rehydration drink when speedy and complete restoration of fluid balance is required (Maughan & Shirreffs, 2010). Studies found that drinking plain water resulted in high urine flow and did not allow participants to remain in a positive fluid balance for very long (because they excreted it quickly) (Lanham-New et al., 2011). Plasma volume was better maintained when electrolytes were existent in the fluid, sodium to be exact (McDermott et al., 2000). The consumption of plain water after exercise- induced dehydration, lead to a fall in plasma osmolality and sodium concentration (Shirreffs, 2003). It is therefore recommended that the sodium lost through sweating, be replaced. Ideally, consuming more sodium than that lost through sweating will lead to euhydration (ideal hydration levels). Sodium also incites glucose absorption in the small intestine through the transport of glucose and sodium, which promotes water absorption (Barnett, 2006; Lanham-New et al., 2011).
Another important factor to mention is the importance of food consumption, as well as fluids (Lanham-New et al., 2011; Oppliger & Bartok, 2002; Shirreffs, 2003). Eating solid food should be encouraged during and after exercise in order to meet other nutritional goals. Post exercise food intake along with flavoured water or sports drink has been investigated and was found to reduce urine volume by 300ml, resulting in good recovery (Coyle, 2004; Sawka et al., 2007).
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