Water. It accounts for 60 per cent of the average adult’s body mass. We can last weeks without food but we only have about a three-day window where we can survive without water, shorter in a warm environment. Every cell in our body relies on water. It’s used in several important functional processes as well as being crucial for maintaining high levels of sport performance.
What is hydration?
Hydration refers to how much water you have in your body at any one time. This is especially important when we consider how physically demanding sport is.
When hydrated, our body is content with the concentration of salt and other important electrolytes in our blood and tissues. These electrolytes create an environment that allows our cells to conduct electrical signals that send messages to our nervous system. Without enough of these electrolytes, muscles can cramp or even fail completely.
In day-to-day living, our electrolyte levels are easily maintained through adequate water and good nutrition. When we’re playing sport or doing strenuous activity we need to be more conscious of replacing what we have lost.
What are the symptoms of dehydration?
Symptoms of dehydration are similar to and intensified by symptoms of heat distress. These include decreased concentration levels, nausea, feeling thirsty, dry mouth, and headaches. If you delay fluid replacement it’s common to feel bloated and sick when you do finally rehydrate. This may also impair suitable intake of match day foods needed for refuelling when playing sport.
The rate at which an individual dehydrates varies depending on several factors like sweat rate, climate, clothing, and general health and fitness levels.
A healthy human body maintains an internal core temperature of around 36-37°C. When playing sport, the body burns fuel like carbohydrates and fat to make muscles contract. This fuel metabolism produces heat that raises the body’s core temperature. This heat needs to be dispersed to avoid damaging the body’s systems or adversely affecting sports performance.
The body can disperse heat in several ways. The method responsible for at least 75 per cent of heat loss is sweating. Our bodies cool down when sweat evaporates from our skin.
What are the symptoms of heat distress?
A small shift in the body’s ideal core temperature can be particularly damaging. Critical and life threatening damage occurs at around 41°C. Between 36-41°C, the body can start showing symptoms of heat distress. These symptoms include decreased fine motor skills and concentration levels, nausea, headaches, vomiting, loss of consciousness, and organ failure.
It’s important to implement heat management and hydration strategies to decrease the symptoms of heat distress and dehydration.
Heat management and hydration strategies
The following strategies help reduce heat stress and maximise sports performance in hot weather. The more strategies athletes use, the better the effect on performance.
Before departing for match: Air conditioning kept 18-20°C
Pre-match: Icy poles before warm up; cold fluids during warm up; and cold fluid, icy poles, cooling collars, and cold towels after warm up
During match: Cold fluids, cooling collars, cold towels, avoid wearing full skins and tight fitting garments
Break or half-time: Icy poles, cold fluid, cooling collars, and cold towels; cold plunge pool and cold showers; air-conditioning at 18°C
Post-match: Cold plunge pool, cold fluids, and cold showers
Back home: Cold air conditioning and cold shower
When drinking sports drinks, it’s important to choose an isotonic product. An isotonic solution contains concentrations similar to sugar and salt found in the body. It’s also the quickest method of rehydration and supply of energy and is important during exercise. Examples of isotonic solutions: Hydralyte Sport, Hydralyte, SOS, SIS, and Endura.
A hypertonic solution contains higher concentrations of salt or sugar in the body and is not ideal for rehydration. These solutions can slow down the hydration process and cause gut upset when consumed during exercise. These types of products are best used when refuelling after exercise if food is not tolerated or available. Examples of hypertonic solutions: Gatorade, Powerade, Staminade, Lucozade, and Aqualyte.
Hypotonic solutions have the lowest concentration of salt and sugar compared to the body’s levels and are easily tolerated when exercising. These often have the lowest levels of added carbohydrate, so are not reliable as an energy source. However, these can be used to replace electrolytes. Examples of these solutions: diluted Hydralyte.
As a general rule, if you are exercising for an hour or less at a moderate intensity, water is suitable and a sports drink is unnecessary. But if you are exercising for longer than an hour or at a high intensity, a sports drink can be beneficial for refuelling and rehydration.
If you spend a significant amount of your day in air-conditioning, it’s important to be thorough with your hydration. It’s common for people to forget to hydrate in cooler temperatures and dehydration can be just as frequent in cool environments as it is in hot weather. This is particularly important to consider when playing sport in an air-conditioned environment.
A common question I am asked by coaches and athletes is whether hydration considerations are the same when you are playing a water sport. In water, your sweat rate is altered and your ability to cool your core body temperature by sweating is compromised.
Being in water can also skew our perception of hydration and people can forget to drink, ending up more dehydrated. Some individuals also find it hard to tolerate many fluids in their stomach when exercising in the heat. If so, the best strategy for fluid intake is having small, frequent sips of an isotonic solution.
More sports nutrition related information
Eliza Freney, Sports Dietitian, Ripen Health www.ripenhealth.com.au
Sports Dietitians Australia, www.sportsdietitians.com.au