Good hydration is important for body functions including cellular metabolism, blood flow, nerve and muscle function. It helps regulate body temperature, lubricates joints and aids digestion. Hydration plays a role in the transportation of red blood cells throughout the body, nutrient absorption, the formation of protein which is essential in the growth and recovery of muscles.
Lack of hydration can lead to early onset of fatigue during exertion, poorer response times, increase risk of injury and a sharp rise in the risk of cramping. Any level of dehydration can negatively affect a swimmer’s performance. A loss of hydration of as little as 2% may affect athletic performance by as much as 10-20%.
Dehydration can cause electrolyte imbalances in the body. These imbalances can lead to symptoms which include thirst, dry mouth, headaches, dizziness, fatigue, muscle cramping and weakness. Along with physical manifestations, metal skills, including focus, judgement and decision making may be compromised.
Alcohol and caffeine can cause dehydration as they are diuretics, a substance that causes increased production of urine by blocking the hormone used to reabsorb water in the kidneys, turning fluids directly into urine.
Swimming carries risks of dehydration because while in the water it is difficult to judge how much fluid is being lost through sweating and being surrounded by water tricks sensory receptor that signal thirst. Urine colour is a good indication of hydration levels, pale to light yellow indicates proper hydration. If you feel thirsty, this is a signal that you need liquids.
Avoiding dehydration is important. Recommendations include drinking 500 ml of water two hours prior to a workout and consistently hydrating throughout a workout. Post workout hydration promotes recovery. Proper hydration, when not exercising, includes consuming 1 liter of water per 30 kg of body weight daily.
FINA has produced great information on hydration within the Nutrition for Aquatic Athletes BOOKLET.