How much should we drink (in regards to sport)?
Short answer – you need to replenish the fluids (and electrolytes) you lose.
For you to work out how much you need to drink the best option is to work out your sweat rate!
Make sure you work out your sweat rate during a few different games, as the weather, how hard you play, how long you play etc. will all change how much you sweat. You will have to take this into consideration when working out how much you will need to drink from game to game. Once you know your sweat rate, you can easily work out an estimate of how much you will sweat in the game.
During play athletes should aim to replace ~80% of fluid loss. As a guide this is about 150-200mL of cold fluid every 10-15 minutes but you should be able to be more precise as you can use your sweat rate.
You should remember that there is no need to try to ‘super-hydrate’ prior to exercise. Your body can only absorb so much fluid before it will need to expel the excess fluids. The risk is that if you over-drink, you may have to inconveniently urinate during exercise. Timing your drinking is important. This is because the kidneys rate of filtration a key limiting factor – ultimately you have to give them time to expel any excess fluids. A wise tactic is to ‘tank-up’ two or more hours prior to exercise. This gives your kidneys a chance to process and eliminate any excess fluids. Then make sure you drink again 5 to 15 minutes prior to exercise.
Working Out Your Sweat Rate
The following procedure may be used by an individual athlete. (It is advised that any calculations are checked with a healthcare professional or registered sports coach)
- Immediately prior to the start of the exercise episode (game or training), measure the pre-exercise body mass (let’s call it ‘A’ in kg) on accurate scales. Ideally in a situation where you can be nude, as any clothing will alter the results. If there is not appropriate place for you to do it nude, wrap a clean, dry towel around your waist. Keep the towel separate and dry, and then use it again when you have to re-weigh yourself after.
- Immediately after the exercise, towel (using a second towel!) off the excess sweat, and measure, (either nude or with the same towel as in step one), the post-exercise body mass (‘B’). Calculate the total body mass change (C = A – B kg).
- Record the drink volume consumed during the exercise episode, between weighings, (D) expressed in kg (Assume 1L = 1 kg and 1 ml = 1g)
- 4. Record the urine volume passed during exercise, between weighings (E) expressed in kg (Assume 1L = 1 kg and 1 ml = 1g). If you haven’t needed to go during the game, try and weigh yourself before you go to the bathroom so you can skip this measurement!
- Calculate the sweat loss (F) based on F = C + D – E (in kg) and express as “Litres”
- Calculate the average sweat rate (G) as F (Litres) divided by the exercise duration in hours.
- Check the calculations with a healthcare professional or sports coach.
Example: An athlete trains for 2 hours, with Pre- and Post- body mass measurements of 70 kg and 68 kg. During the episode he drinks 1000 ml water and passes 500 ml urine. Determine his average sweat rate for that exercise under the specific climate conditions.
C = A – B = (70 – 68 kg) = 2 kg
F = C + D – E = (2 + 1 – 0.5 kg) = 2.5 kg = 2.5 Litres
G, the average sweat rate = 2.5 L / 2 hours = 1.25 L/hour
The athlete is losing fluid from perspiration at a rate of 1.25 L/hour
If above is too much math, just go to the link http://www.triharder.com/THM_SwRate.aspx and fill out the online calculator.
‘Pet peeve’ Bottled water
Don’t drink bottled water if you’re playing in Melbourne – Bottled water has been shown to be is no purer than tap water, and both may contain bacteria or carcinogens. That’s not to mention the huge environmental footprint that associated with the manufacturing and transport of bottled water. Melbourne has some of the world’s best water, all on tap and much cheaper!
If you needed another reason to avoid bottled water – Oestrogen-mimicking chemicals can leach into drinking water, and other beverages, from bottles made from certain plastics.
What should we drink?
The aim of the drink should again be aimed to replace what you lose!
Recent research also shows that sports players can a significant amount of sodium during long play in the heat, some male players were losing up to 2 grams of sodium in a single session! Solutes (‘electrolytes’) in sweat make up about 0.2–1%. (Water in urine makes up about 96% leaving about 4% for other waste ‘products’). But remember you will sweat less and therefore lose less sodium in colder weather.
Examples sources of fluid and electrolytes:
BEST – water, fitness waters, sport beverages, and flavoured cordial
In my opinion, you should say NO to alcohol and caffeinated drinks. But if you are not willing to consider that option try swapping (decaffeinated for caffeinated) or alternating (club soda/alcohol)
When should we drink?
Before the game!
Tank up with 500-1000mL of fluid two or more hours pre-match. Then as close to match time as you can tolerate (5-15 mins) drink ~250mL (for example, on the way to your match pre-hydrate) keeping in mind the volume tolerated will be specific to the individual.
During the game!
During play athletes should aim to replace at least ~80% of fluid loss Carbohydrates should be replenished at a rate of 30–60g of carbohydrate per hour. Remember carbs can be in the drinks! Examples of 50g of carbs: one large banana OR 750mL of sports drink
After the game!
Immediately initiate fluid replacement.
From the minute the game ends you should be thinking about recovery!
Recovery will be discussed in a blog at a later date. This one is already long enough!
- Limit/avoid caffeinated beverages (iced tea, coffee, cola), especially right before (~24 hours) and during the recovery period after match play (~72 hours). These do not hydrate as they act as diuretics
- You should be consuming enough fluids throughout the day so your urine is a light or pale yellow colour before starting a match
- Make sure you practice drinking (water!) during training. As this helps your body get use to drinking during an event, it also makes it a habit to drink while playing and most importantly it replenishes fluids lost when training!
Is thirst a good indication of when to drink?
Man has evolved (apologies to those who believe otherwise) with kidneys that can conserve water by producing concentrated urine (reducing water loss), and in fact the osmotic (or ‘water level’) threshold for the release of vasopressin (the enzyme which stimulates the kidneys to conserve fluid by concentrating the urine) is lower than that which stimulates thirst, which in turn is lower than the osmolality at which dehydration is considered to start.
Order of the body’s response to dehydration:
So if you miss the initial cues of thirst – or don’t have the timely opportunity to do something about it you risk falling into a state of dehydration. Many will say that dehydration causes deterioration in performance; I think that this is questionable. However, if you follow the advice given so far, you will not suffer because of your hydration levels.
You also have to consider the time it takes to circulate and resupply the water and electrolytes throughout the body. As with most things, the prevention is better than the cure! Don’t get slack and rely on your thirst levels, be proactive!
Water is good for us, but too much can dilute your body’s sodium levels low enough to increase other medical problems including muscle cramping. This leads us perfectly onto the next blog!
It would be great to see what everyone else is thinking. To do this please leave a comment below. I would love to hear any neat tips for staying hydrated and it would be great to hear from you if you have a different way of thinking about hydration. Please share your knowledge!