Hydration is a bit of a contentious subject when it comes to endurance sports, drinking too little will detriment performance, while drinking too much can cause create extra logistics and carrying extra weight
There are generally too opinions:
- drink to avoid thirst
- positive hydration strategy
Nutrionists working with pro teams have different opinions. Nigel Mitchel (team sky) was an advocate of the positive hydration strategy as part of Team Sky’s 2012 success. The idea is that you can’t drink too much. On the other, in a seminar on nutrition Rob Child (MTN Quebeka) said ‘drink when you are thirsty’.
As these are both top-level nutritionists and sports scientists I don’t have much too add to this discussion, on a scientific level. However, one thing to bear in mind are some of the risks regarding heat and hydration. This article has a good discussion on the subject http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1872071/
So how much should you drink?
Start with common sense, drink enough so you don’t get thirsty. However bear in mind that there is a ceiling limit for water absorption. Even if you are becoming dehydrated, drinking more than 800ml of water per hour can cause hyponatremia, dangerously low sodium levels.
Use a hydration strategy
When I raced XC, I used a nutrition/hydration strategy. Events were relatively short (<2hrs), but the temperature could be extreme. In 2013 I raced a National XC series race on the hottest day of the year, which included an exposed windless climb at <10mph with isolated temperatures hitting over 40 degrees Celsius.
My strategy in this race was to receive 750ml water with electrolytes (no fuel) each lap (every 15mins). Each time I took a bottle I doused myself with most of it and drank 100-200ml. I then used energy gels as fuel in addition to this.
In road racing, I generally use two nutrition strategies, one is for cold/wet weather than other for summer. In the summer I drink just water/electrolytes plus food/gels. In cold/wet races, I use a strong energy drink, a bottle of water plus energy gels/food.
Simple hydration strategy for long races (>2.5hrs)
The main challenge with road racing is the volume of liquid you need races last more than 3hrs in hot weather, this could be as much as 4 lites, which is impractical to carry on your bike, in which case you need someone to feed for you.
- Work out the maximum you sweat in litres/hr, during a hard indoor training session
- Estimate the maximum duration of your race
- Work out the total volume you could sweat in this time
- Try to make sure you have this volume of water/electrolytes available to you for the race.
- During the first hour, drink regularly.
- For the rest of the race continue to drink according to your judgement
The key thing with this strategy is that you have enough water available to you, either on your bike, or with someone who can feed for you.
Work out how much you sweat in hard training.
If you want to be sure you are drinking the right amount, you could work out how much you sweat per hour. This could be particularly useful, for riders who are very small or very tall and light.
- use a training environment similar to the one you will race in, for the UK 20-22 degrees is about right.
- Use a powerful fan. This will mimic the airflow while you are cycling, to an extent.
- Weigh yourself without clothes/shoes before the session. Use the most accurate scales you can get your hands on.
- Do a hard 60min session
- Start with drink bottles full with a measured amount of water. Weigh any food you eat during the session.
- if you need to go to the toilet during the session weigh yourself before and after.
- Dry yourself after the session and wait a few minutes to allow your skin to dry.
- Weigh yourself without clothes again
- Work out the net fluid loss
I weighed 74.1kg at the start of the session, 73.7kg after the session and I drank 750g of fluid, I also lost 350g of fluid when going to the toilet. This means I sweated of 800ml of fluid during an hour.
Bear in mind there are all sorts of factors that will affect this result, the idea is just to give you an idea of how much fluid you use when training.
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