Before becoming our Practice Manager at The Melbourne Sports Medicine Centre, in a former life, Julie Tatnell was a leading Sports Dietitian. From this background Julie was keen to include in this Summer Newsletter some information on the importance of athletes hydrating appropriately especially during summer sports. Frequently she has seen athletes needlessly exposing themselves to harm and being unable to perform to their optimum due to inadequate hydration. These days our Sports Dietitian is Feng-Yuan Liu.
Usually inadequate hydration stems from the athlete not fully understanding his or her body’s response to the physiological stresses that their chosen sport places on them, particularly in hot conditions.
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 action 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. This highlights the importance of getting to know your sweat rate and knowing how much you should be drinking.
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. 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.
Drinking more fluid than is comfortable, in any conditions, has the potential to interfere with your performance. 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 before, during and after exercise. Sports dietitians routinely measure an athlete’s sweat rate during training and competition in a range of environmental conditions, to provide them with the information required to design an individual fluid plan.
Follow these easy steps to measure your fluid losses:
- Weigh yourself in minimal clothing, as close to the start of exercise as possible. Ideally you should empty your bladder before weighing.
- Commence exercise session.
- Weigh yourself at the end of your session, in minimal clothing again, ensuring you towel off any excess sweat from your body.
- Your weight change during exercise reflects your total fluid loss; i.e. the difference between your sweat losses and fluid intake.
- Remember that weight loss during exercise is primarily water loss (not fat loss), and needs to be replaced soon after finishing exercise.
- Other fluid losses come from breathing, spitting, vomiting as well as from passing urine. Sweat losses can be monitored to give you an idea of how much fluid to replace around training sessions and competition.
The AIS has provided us with an example of how to calculate our own sweat rate.
Pre-exercise weight - 55 kg
Post-exercise weight - 53.5 kg
Volume of fluid consumed during exercise (1 L) - 1 kg
Estimated urine losses – 500ml
Exercise duration - 2 hrs
Fluid deficit (L) = 55 kg - 53.5 kg = 1.5 kg
Total sweat loss (L) = 1.5 kg + 1 kg - 500ml = 2 kg
Sweat rate (L/h) = 2 kg/2 h = 1 L/h.
Whilst knowing your own individual sweat rate is the key to managing your hydration strategy, the AIS also provides us with a useful guide of the average fluid loss for sportsmen and sportswomen under for different conditions for various sporting activities. Some examples are shown below and a more complete list of sports can be found by using the link.
It is interesting to note how the intensity of exercise and the ambient temperature affect the rate of fluid loss and that there are real differences between the average rate in men and women.
Our Sports Dietitian Feng-Yuan Liu has also written some practical tips to staying hydrated in Summer when exercising:
Aim to start with an optimal level of hydration before exercising. This might sound very silly when spelt out like that, but it is concerning how many people are not getting enough hydration on a day to day basis! A good guideline is 30-40ml per kg body weight. So, if you weigh 70kg, you need to aim for 2.1-2.8L of fluids a day!
Check your urine. How well-hydrated you are can also be tell-tale through the colour of your urine. Optimally, you should have pale yellow coloured urine – if it is dark, it means you are dehydrated, and if it is clear, it means you aren’t retaining enough fluids – time to up the electrolytes!
Avoid alcohol and caffeine. Alcohol and caffeine are both diuretics and make your body lose more fluids. So, when you know you will be exercising, or competing in a sport / race, try to avoid alcohol leading into the event, and make sure you have the above 2 tips covered!
For exercise less than an hour, drink water. Often I see people go do a 30-60min session at the gym and they are throwing back sports drinks. Whilst this isn’t harmful, it is also not necessary. When you are exercising for short durations (less than an hour), water is sufficient for hydration. Of course, there are the ones who have very salty sweat, in which case, an electrolyte-filled sports drink may be necessary. However, for the majority, water is all we need. If you feel that you might be a big “salty sweater”, you may benefit from a sweat test. Ask your sports dietitian and they can direct you to where you can get this done.
For exercise longer than an hour, add the electrolytes. If you are doing a long event, aim to hydrate with a sports drink that is abundant in electrolytes and has about 6-8% carbohydrates for re-fuelling. A good one would be Gatorade.
Consider your overall diet, as hydration is only one aspect of it all! Do not neglect a well balanced, nutrient rich diet. For athletes, it is important to consider the amounts of protein, carbohydrates and fats in your diet, especially around training time. Focusing on foods that are nutrient dense ensures that you are getting a lot of your micronutrients as well as the macros. If you are unsure whether you are eating correctly for your training, speak to a sports dietitian who can assist you in figuring this out!
Stay hydrated and have a great Summer!