Even at rest adults lose 2 to 3 litres of fluids daily through the skin, waste products and by breathing air out of the lungs. During exercise there is a dramatic increase in water losses from breathing due to increased respiration rates and sweating as the body seeks to dissipate the excess heat. Most of this must be replenished by intake of food and liquids to achieve water balance and avoid the effects of dehydration. A fluid loss as low as 2% of body weight can have an effect on performance. Thirst is often not an adequate indicator as thirst cues begin when body water loss is about 1% of body weight but even then most athletes learn to override them and only start to notice them when we are well on our way to more deleterious levels of dehydration.

BY DR AMY JOY LANOU, PhD

taying in water balance as an athlete is a challenge throughout the year, but during intense pre-season conditioning, the degree to which an athlete succeeds at hydration can make or break the effectiveness of his or her efforts.

S

IMPORTANCE OF ADEQUATE HYDRATION Researchers and endurance athletes have known for a long time that body water losses of 3–4% of body weight, decrease endurance and muscular strength during prolonged exercise performance. Recent research shows that modestly reduced body water attenuates strength (by approximately 2%), power (by approximately 3%), and high intensity endurance (maximal activities lasting >30 seconds but <2 minutes; by approximately 10%) (1). Skills performance (such as cricket bowling accuracy, football/ soccer skills performance) (2,3), and related cognitive functioning (such as headache, tiredness, reduced alertness, and greater difficulty concentrating) have been shown to be impacted at water losses of approximately 2% of body weight (4).

Environmental temperature matters. For many athletes training or competing in a cold or temperate environment (-22o

C), a

less than 2% loss of body water is tolerated without significant risk to well-being or exercise endurance. However, if the ambient temperature is hot (30o

C or more), the same

levels of dehydration impairs performance and increases the danger of experiencing a heat injury (5).

PROBLEMS ASSOCIATED WITH CHRONIC LOW-LEVEL DEHYDRATION Signs of chronic dehydration include morning headaches, darkly coloured concentrated urine, and infrequent urination or low urine volume. A recent review article reported that maintaining good hydration status can reduce the risk of urinary tract infections, constipation, dental disease, gallstones and glaucoma. In addition, good hydration status has been shown to be useful in the treatment or management of various heart and vascular diseases including high blood pressure, coronary heart disease and stroke (6).

WATER BALANCE Even at rest, adults lose 2–3 litres of fluids daily through the skin (~750 mls via insensible sweating), in the faeces (~200 mls), in the urine (~1500 mls) and by breathing air out of the lungs (~350 mls). A small amount of water

12 sportEX dynamics 2008:16(April):12-14