The world is counting down to another Big Summer Games, as usual surrounded by excitement, drama and controversy. The athletes competing in Rio de Janeiro should expect warm winter temperatures with little rainfall, according to the official weather information booklet from the Games organisers6. Average temperatures in brazil in August are 230C, with average minimums and maximums 19.6oC and 28.7oC respectively.
Discussions about the weather and sport inevitably lead to the popular topic of hydration and exercise. Today’s article is a foray into the complicated world of fluid intake around sport or exercise. Whilst the majority of the Australian population will only ever be armchair participants in these games, many Australians participate in many forms of sport and exercise. In this sunburnt country full of environmental extremes, it is important that we have accurate and current knowledge about appropriate hydration. However, it is an absolute minefield of confusing information for practitioners and the public alike. Truly independent guidelines can be hard to find as sports drink companies are interwoven with research and sporting institutes.
Why is Fluid Important for Exercise?
Water is a vital component of the human body, and has many important functions, including the maintenance of blood volume and pressure, lubrication of joints & body tissues and the regulation of body temperature3,4. During exercise the body’s temperature increases, depending upon the intensity and duration of exercise, the environmental conditions amongst other factors. The body cools itself by producing sweat, which contains water and electrolytes. The evaporation of sweat is the primary method of heat loss, but this also causes the loss of body fluid. Significant losses of fluid lead to dehydration, which can have adverse performance effects, such as2:
- increased heart rate
- impaired heat regulation
- reduced mental function
- gastrointestinal upset
- increased perceived exertion, meaning that exercise feels harder than usual
Therefore, drinking fluid is necessary to replace the fluid lost through sweat. However, drinking too much fluid also has its problems. A rare but dangerous condition called exercise-associated hyponatremia exists, typically in long distance athletes such as marathon runners, which is primarily caused by excessive consumption of fluid2,4,5. Low sodium levels in blood develop, which can cause nonspecific symptoms of bloating and headaches to confusion, coma and has been responsible for fatalities in endurance events1,5.
How much fluid to drink?
Individual needs vary. The current recommended approach is the common sense approach of “drinking to thirst”, although, it is recognised that using thirst alone can only replenish about 75% of fluid loss5. Individuals involved in serious endurance exercise may consider measuring their sweat rates, to determine how much fluid they lose during their event, and therefore, calculate how much fluid they need to consume. An accredited sports dietician should be consulted for this process, and can develop an individualised fluid plan5.
A simple way of determining fluid loss during exercise is to weigh yourself before and after training, in minimal clothing and with dry skin5. Weight loss greater than 2-3% marks the level of dehydration that can adversely affect performance4.
What fluid should I drink?
- The Australian Institute of Sport make the following criteria for fluid selection during exercise2:
- A palatable flavour will encourage a greater fluid intake
- Should contain 6-8% carbohydrate
- Should contain electrolytes such as potassium and sodium
- Should be non-carbonated
- Water is effective fluid replacement for low intensity and short duration activity3
- Drink small amounts of fluid as this maximises absorption into the body. Large amounts of fluid stimulate urine production and can cause gastrointestinal upset3,5
- If using powdered sports drink, follow instructions exactly. Incorrect preparation may impair performance and lead to gastrointestinal discomfort3.
- Specific fluid replacement quantities are not recommended due to everyone’s individual needs5
- Ensure you start exercise hydrated to lower the risk of becoming dehydrated during exercise3
- Aim for pale, straw coloured urine in the hours prior to exercise3,5
- Avoid excessive fluid intake just prior to exercise as this can lead to abdominal discomfort5
Exercise <1 hour duration:
- Drink to thirst
- Fluid replacement may not be necessary, unless hot environmental conditions
- Water is sufficient3,5
Exercise 1-2 hours duration & continuous:
- Fluid replacement will probably be necessary5
- Carbohydrate can help maintain performance by topping up fuel stores in the exercising muscles & brain5
Exercise longer than 2 continuous hours:
- Fluid and carbohydrate replacement will be necessary5
- Type and amount will depend upon the environmental conditions, intensity, individual’s sweat rate and preferences3.
- Continue to drink as fluid loss continues due to sweat and urine losses
- Rehydrate until urine returns to pale colour5
To find out more about the topic and to improve your health and performance, come on in and see us at Absolute, 199 William Street.
Written by Performance Coach and Pilates Specialist Liz Hewett
- Almond, CSD et al (2005), Hyponatremia among Runners in the Boston Marathon. New England Journal of Medicine 352 (15); 1549-1556.
- http://www.ausport.gov.au/ais/nutrition/faq/hydration. Accessed 29.7.16
- sportsdieticians.com.au. Accessed 27.7.16
- Casa DJ, Clarkson PM & Roberts WO. (2005). American College of Sports Medicine Roundtable on hydration and physical activity: consensus statement. Current Sports Medicine Reports 4:115-127.
- Lawrence, J. (2016). Running water: how much to athletes need to drink? Medicine Today 17 (7); 59-61.
- National Institute of Meteorology- INMET, January 2015. Weather information for the Olympic and Paralympic Games in Rio de Janeiro 2016. fei.org/system/files. Accessed 27.7.16