Water is essential to maintain blood volume, regulate body temperature and allow muscle contractions to take place. During exercise, the main way the body maintains optimal body temperature is by sweating. Heat is removed from the body when beads of sweat on the skin evaporate, resulting in a loss of body fluid. Sweat production, and therefore fluid loss, increases with a rise in ambient temperature and humidity, as well as with an increase in exercise intensity.
Drinking fluid during exercise is necessary to replace fluids lost in sweat. This will reduce the risk of heat stress, maintain normal muscle function, and prevent performance decreases due to dehydration. In most cases during exercise, the rates of sweat loss are higher than the rate you can drink, so most athletes get into fluid deficit. Therefore, fluid guidelines promote drinking more fluid to reduce the deficit and potential performance detriments associated with dehydration. However, it is also important to acknowledge that it is possible to over-drink during exercise.
Drinking more fluid than is comfortable, in any conditions, has the potential to interfere with your performance. In cool weather or when the exercise pace is gentle, the rate of sweat loss may be quite low. It is unnecessary and potentially dangerous to drink at rates that are far greater than sweat losses. Knowing your sweat rate can give you an indication of how much you should be drinking during exercise.
Dehydration and Performance
As dehydration increases, there is a gradual reduction in physical and mental performance. There is an increase in heart rate and body temperature, and an increased perception of how hard the exercise feels, especially when exercising in the heat. A loss of fluid equal to 2% of body mass is sufficient to cause dehydration. Dehydration of greater than 2% loss of body weight increases the risk of nausea, vomiting, diarrhoea, and other gastro-intestinal problems during exercise.
Dehydration reduces the rate of fluid absorption from the intestines, making it more difficult to reverse the fluid deficit. You may end up feeling bloated and sick if you delay fluid replacement.
Warning signs of dehydration are:- * Lack of energy * Early fatigue during exercise * Clammy or flushed skin * Not needing to go to the toilet * Nausea * Headache * Disorientation * Shortness of breath
(Headache, Disorientation and Shortness of breath are signs of advanced dehydration)
Drinking fluid during exercise helps to prevent a drop in performance caused by dehydration, and fluid after exercise will re-hydrate you. The amount of fluid and the timing of drinks depend on the individual and the sport. Here are some tips:  Always start exercise well hydrated; this will lower the risk of becoming dehydrated during sport. There is minimal performance benefit to being over-hydrated as drinking excessive amounts of fluid before exercise causes increased urination and feeling bloated. * Develop a plan for drinking during exercise based on your own sweat rates * Immediately after exercise, monitor your weight change to estimate your final fluid deficit * During recovery, you will continue to lose fluids through sweating and urine losses, so plan to replace this fluid deficit over the next 2-6 hours you will need to drink 1250-1500mL to fully re-hydrate
Sources of fluids
Water – this is considered to be adequate fluid suitable for most exercise.
Sports Drinks – these aim to provide three nutrients, these are:- * Carbohydrates to replace energy – these are usually glucose, fructose and sucrose which are absorbed quickly * Water to replace fluid and * Electrolytes to replace the minerals that you lose due to sweating - these are sodium and potassium as both are lost by sweating
Hypertonic is intended as a thirst quencher. Hypotonic drinks give the athlete little energy in the form of sugars. A hypotonic sports drink is taken up by the body more quickly than just water. Ideal for recreational sports or shorter or less strenuous exertion.
Isotonic generally contains between 4g and 8g of sugar (carbohydrates) per 100ml. An isotonic drink is taken up by the body about as quickly as water. They are intended to quench thirst and provide energy to the body. Ideal for endurance sports.
Hypotonic generally has more than 8g of sugar (carbohydrates) per 100ml. It is primarily intended to supply energy. The thirst quenching effect is secondary. Hypertonic drinks are taken up more slowly than water. Ideal for use 30 to 60 minutes before sports/training/exertion and immediately after sports/training/exertion. Hypertonic drinks are also useful for athletes or workers who find that they need a bit more energy during their training/competition/ exertion. Also ideal for less strenuous, long duration exertions such as studying, driving, gaming, etc.