Your sweat rate is used to estimate how much fluid you need to replace during and after sport. This can be measured by looking at your weight change over several exercise bouts to get a feel for your own personal sweat rates under different exercise and environmental conditions, where:
Sweat loss (mL) = change in body mass (g) + fluid intake (mL) - urine losses (g)
Weighing yourself, immediately before and after exercise gives you a good idea of how much fluid you actually lose during exercise. The difference in weight represents fluid loss (ie. 1kg loss equals to approximately 1L (1000mL) sweat). Once you know how much you lose per hour of exercise, generally it's best to replace 80% while exercising (so in this case, 800mL). After you finish exercising, you should drink 150% of your fluid deficit. For example, if you are still 400mL down will mean replacing 600mL fluid after exercise.
Sweat rates vary greatly between individuals, with females tending to sweat less than males. For example, even within one sporting team doing similar work, sweat rates can range from 600 – 1200 mL/hr for females, and 800-1400 mL/hr for males1. Your personal fluid target should be scheduled, so that you start drinking early on and consistently throughout the exercise bout rather than leaving it all to the later stages. If you leave it too late, it’s likely your stomach won’t be as receptive to absorbing the fluid since the blood flow will have shifted to other areas of your body, such as your muscles. These fluid intake targets should be practiced in training so that you train yourself to drink more, and you can make sure you’re drinking within gastrointestinal (stomach) tolerance.
To calculate how much sweat you lose when training or in competition, you will need to:
Weigh yourself (with minimal clothing - eg. no hat, socks, shoes, t-shirt) before exercise
Exercise for one hour at your targeted intensity**
Track your fluid intake during exercise (measure in mls)
Record weight (with minimal clothing) after exercise
The above method determines your hourly sweat rate by adding the difference in your weight before/after exercise to the fluid consumed (step 3).
Note the environmental conditions on this day, and repeat the measurements on another day when they are different (cooler, warmer). This will give you an idea of how different conditions affect your sweat rate.
Disclaimer: This Method is only a rough estimate of recommended fluid intake. For serious training and competing requirements, please consult a sports dietitian.
REFERENCES:
Broad EM, Burke LM, Cox GR, Heeley P, Riley M. 1996. Body weight changes and voluntary fluid intakes during training and competition sessions in team sports.
Starting exercise properly hydrated gives you the best chance of minimising dehydration as you train, play, or race hard. It can also help keep your blood volume at optimal levels, and allows you to sweat to remove heat effectively. Athletes that are well hydrated are also likely to have better concentration and skill learning ability. So there are many good reasons to use POWERADE ION4 to keep you well hydrated!
The following are some examples of what could happen to your body when you are dehydrated:
Thicker blood: When you start to dehydrate, your blood volume decreases and starts to thicken and slow. This puts pressure on your heart, making it work harder to pump oxygen and glucose to your muscles.
Muscles fatigue: Your active muscles lose muscle strength and fatigue.
Mental fatigue: Reaction times, concentration and decision-making ability decrease.
Overheating: As the cooling effect of sweating decreases due to less fluid in your body, your core temperature rises.
It's important to recognise the following signs of dehydration. Some of the symptoms include:
When you're thirsty, it's your body's way of saying you're already dehydrated. As little as 2% dehydration (that is, 1.4kg loss in a 70kg person) may lead to a noticeable decrease in performance. Dehydration results in increased body temperature, increased heart rate, increased ratings of effort, reduced physical performance, and reduced mental performance1. Hence, drinking during exercise can help minimise detrimental effects, especially during more prolonged and / or higher intensities of exercise. There is also now some evidence that drinking cool fluids actually helps keep your body temperature down when you're exercising in the heat as well2. Mild dehydration can affect physical and mental performance, while severe dehydration can be life-threatening. Dehydration can develop quickly under some conditions, such as extreme heat. To avoid dehydration and perform at your best, pay attention to your thirst and make sure you consume plenty of fluids during the day.
The colour of urine is the simplest indication of your level of hydration and is usually accurate. If it's clear or lightly coloured you're generally fine (unless you've just had large volumes of water without a sports drink or salty food - hence not retaining any fluid consumed); if it's dark yellow you're dehydrated (or have consumed large amounts of vitamin B and/or C through a supplement).
Check out the Hydration Calculator to estimate rough fluid requirements for your exercise or sport.
Hyponatraemia, or low sodium levels in the blood. This occurs when more fluid is consumed than can be effectively cleared by the kidneys (which tend to reduce their function during exercise). The symptom of hyponatraemia can be similar to dehydration - headaches (due to swelling of the brain), disorientation, nausea and vomiting 1. Most reports of hyponatraemia have occurred in ultra-endurance running events (often greater than six to eight hours), with those most at risk being slower runners with plenty of opportunity to drink. Drinking a sports drink doesn't necessarily reduce the risk, although it may help to lower the risk if volumes consumed and sweat rates are matched. The main issue is to not drink so much that you gain weight during the event 2,3, so aim to finish exercise at the same, or a slightly lower, body weight than that with which you started. Knowing your own personal sweat rates under different weather conditions is a great way to ensure the fluid volume you take in is close to what you need - not too much and not too little. See "How to Determine Your Personal Sweat Rate" for help with this.
