The Effect of Hydration and Nutrition on Athlete Performance

There are many factors that can influence the hydration status of athletes at the 2014 FIFA World Cup in Brazil. It is important for an athlete to be well hydrated prior to exercise, as dehydration (or hypohydration) can lead to a significant decrease in performance and can increase the risk of heat illness.

Most forms of strenuous physical exercise require the formation and vaporization of sweat as a principal means of heat removal. Sweat losses produce a body water deficit, in which the reduced volume of body fluids contains a greater than normal concentration of dissolved electrolyte substances such as sodium, magnesium and potassium; this is known as hypertonic hypovolemia. Such dehydration can cause a lack of performance through cramps in the calves and hamstrings, a fall in concentration levels, and a drop in the ability to dribble and keep possession of the football. The affects of such levels of nutrition and hydration are discussed in the interview with Mildre Souza, of CR Vasco da Gama, in our World Cup Special Feature. Clinical biochemistry techniques are used to determine the hydration status of athletes, such as blood marker, urine and body weight analyses.

Measurements of hydration
There are many methods for determining hydration status, including monitoring body mass changes, measuring various blood markers (plasma osmolality, plasma sodium), and biochemistry analysis of urine (urinalysis) using clinical biochemistry analyzers.

Body weight changes
A very simple way to determine the level of dehydration is to monitor body weight changes before and after exercise. Sweat patches can also be used to measure and analyze the quantity of sweat loss from the body.

Blood markers
Blood-borne markers of hydration other than osmolality include plasma volume, plasma sodium, and concentrations of fluid regulatory hormones in plasma. These markers all require blood sampling, so are the more labor-intensive method of hydration analysis. An increase in plasma osmotic pressure (osmolality) is proportional to the decrease in total body water and the level of plasma sodium. Plasma volume also decreases proportionally with the level of dehydration. Such plasma volume changes can be estimated from hemoglobin and hematocrit levels in blood analyses, but accurate measurement of these variables requires considerable controls for other factors.

Fluid regulatory hormones, such as arginine-vasopressin and aldosterone, respond to body fluid volume and osmolality, but the hormones are easily altered by exercise and heat acclimation - both of which will affect the athletes in Brazil - and require more expensive and complicated analysis techniques. Although all plasma markers for hydration assessment involve blood sampling with varying degrees of subsequent analytical difficulty, plasma osmolality is the simplest, most accurate and most reliable plasma marker for tracking hydration changes.

Urinalysis
Urinalysis has been shown to be a most valid and reliable method for determining moderate changes in fluid balance. The simplest method is to look at the urine color, using a color scale to compare to the urine - essentially, the darker the urine, the more dehydrated you are. Other, more scientific biomarker urine tests, such as urine specific gravity, urine osmolality, and urine color are only minimally better at determining hydration level.

Summary
For footballers playing in the World Cup 2014 in Brazil, hydration will be a very serious component of their preparation for each match and training session due to the heat, high humidity and air quality. If pre-match analyses show that an athlete is not drinking enough fluid to maintain adequate hydration levels for the match period, then advice may be given to increase fluid intake or to rehydrate more regularly. Changes to hydration strategies for heat and humidity include making fluids higher in electrolytes such as magnesium, sodium and potassium, but also making the fluid more palatable for regular consumption.