Endurance Hydration Calculator

Fluid & Multiple Transportable Carbohydrate Calculator

After answering the same questions a few times over the years, we decided to throw together a little nutrition calculator. Its based on some basic principles of sports nutrition, which are easy enough to understand, but in practice, are quite difficult to calculate. The calculator below is designed for athletes of all abilities, from the weekend warrior, all the way up to ultra-endurance athletes.

The idea is that you tell us what you put in your bottle, and how long it takes to drink it. Simple enough. We then do a few calculations and let you know how well your mix compares with best practice.

Most people will just be adding water and R-Line, but we have added a box to include some R-Line Reload Gel as well. This is for the really advanced athletes, especially the ultra endurance athletes who have a higher risk of gastrointestinal upset and want to really fine tune their glucose to fructose ratio.

We’ve put in some numbers to start with. If you are too far astray you will get some warnings pop up. You’ll find that there is a fair bit of flexibility for you to work with.

Once you have your numbers in place, you can check out the articles at the bottom of the page, which might give you a little more insight into your race day nutrition strategy.

How Much Should You Be Drinking?

The answer to this question of how much to drink is both staggeringly complicated, and unbelievably simple.

A little history on hydration recommendations…

In 1996 the American College of Sports Medicine (ACSM) released their Position Stand: Exercise and Fluid Replacement. This document recommended 600 – 1200 ml per hour of fluids. This seems a little high nowadays.

In the subsequent years, there were a few tragic deaths due to hyponatremia (in short, over drinking while exercising). This hadn’t been such a problem in earlier years of endurance sport, so a few alarm bells went off.

The International Marathon Medical Directors Association (IMMDA) released their own guidance in 2002 that had a recommendation to 400 – 800 ml per hour. This work was led by a chap who had a lot of expertise in hyponatremia (over drinking).

In 2005 the ACSM had another go at it, and released their Roundtable on Hydration and Physical Activity: Consensus Statements. This document doesn’t give a figure at all for how much you should drink per hour. Instead, they say you should aim to keep weight loss to less than 2%, and make sure you don’t drink so much that you put on weight.

Of course, the IMMDA had another crack at coming up with something simple and more or less said that in modern marathons, there are so many different body weights, that 400-800 ml per hour might not be suitable. The advice, and we’re not kidding here, is just drink if you’re thirsty and not so much you are peeing too much. Genius.

We’ve taken a little liberty to paraphrase some of this info above to try and keep it simple. These are highly complicated papers on a highly complicated and controversial topic. We recommend you download these documents and read them yourselves. They are all freely available on the internet. They also give great info on carb requirements, cramping, recovery and many other topics. They really are essential reading for anyone pushing their limits.

At R-Line, we’re big fans of the “drink if you’re thirsty” philosophy as a starting point for any strategy.

What are your Carbohydrate Requirements?

In brief:

  • Keep your total carbohydrate consumption above 14g per hour as an absolute lower limit if you are doing endurance sports
  • Aim for between 30g and 60g carbohydrates per hour
  • Keep your fructose consumption below 30g per hour
  • Keep your glucose consumption below 60g per hour
  • If you are an elite athlete and really pushing things, the upper limit is around 90g per hour of carbs. This is from 60g glucose and 30g fructose.
  • 2:1 ratio of glucose to fructose, or thereabouts, is a sensible ratio for most people.

Some research has been done to find the bottom limit to what is useful for endurance athletes. 14g per hour of carbohydrate seemed to be where the marker lay.

Most guidance calls for between 30g and 60g per hour and this is a sensible starting point for most endurance athletes.

Your body won’t be able to process more than 30g fructose or 60g of glucose so don’t try, it won’t end well. Aim for this as an upper limit.

Once again, this is a really complicated topic. Glucose and fructose are similar, but not the same and they are absorbed and used by completely different pathways. Also, some people don’t process fructose well, so if they aim for 30g per hour, they’re going to end up with a sore belly. For these people, we recommend mixing a little Reload Gel with their R-Line Electrolyte Drink to reduce the glucose to fructose ratio while still getting a decent amount of electrolytes.

Why Did My Stomach Blow a Gasket?

Gastrointestinal distress. Such a lovely all encompassing term, right? Lets not go into too much detail on what it might mean eh!

Stated simply, you’ve put too much in.

Look closely at four things:

  1. The glucose to fructose ratio. If you are taking on too much fructose, you might find yourself in a portaloo as your PB becomes a distant dream.
  2. The carbohydrate concentration in your tummy. You don’t want to go too much over 8% carbs. Your body will sense a high level of carbs in your stomach and turn off the valve that feeds the small intestine. This means you’ll be running around with a full gut that won’t empty. The general rule is this – the higher the concentration of carbs, the slower your stomach will empty.
  3. The total carbs per hour. Once again, your intestines can only handle so much so don’t try to overdo things otherwise the carbs will accumulate in your intestines.
  4. Not enough fructose. This one is a little counterintuitive. Back in the 90’s it was believed that only glucose played a role and fructose was not needed. This resulted in drinks that were 100% glucose and no fructose. People who were trying to push their limits, were trying to push the 60 g per hour barrier instead of the 90 g per hour barrier. By adding some fructose, the carb rates can enter that 60-90g range with ease, and that can mean a much nicer belly experience.
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