Welcome to the Blog of Karl Alexander - Ironman Triathlete, Road Racing Cyclist and Runner.

Monday, 23 August 2010

Solid V's Liquid: Fuelling an Ironman

A practice that’s on the increase, especially with Professional Triathletes, is a liquid only fuelling strategy whilst on the bike. With athletes obtaining all the calories and nutrients required from fluids with a few additional energy gels are carried just in case the athlete feels in need of a few extra calories.

But for those of us not lucky enough to have Nutritional Supplement endorsement deals, is it a viable option whilst racing an Ironman?

Firstly, let’s look at what is available to athletes at aid stations at an Ironman event, in the UK we are given the choice of Gatorade and water distributed in 700ml bike bottles (handy if you have a compact or small frame!!) as our fluid options and Powerbar Performance bars in various flavours as our ‘solid’ fuel. The run course aid station menu’s are slightly larger offering Powerbar Gels, again in various flavours, Gatorade, Water, flat cola and bananas. You will also have the option of your ‘special needs’ bag should you require any additional items.

So let’s look at the nutritional values of the items available on the bike course:


Calories per 100ml/100g


106kj (25kcal)/100ml


0kj (0kcal)/100ml

Powerbar Performance Bars

1528kj (365kcal)/100g

In a 700ml bike bottle there is potentially 742kj or 175kcal. The bars are always handed up to athletes cut in half, each full bar weighs 60g so the calories available from 30g (half a bar) is 458kj or 124kcal.

Let’s assume that the average athlete will require in the region of 3,000 to 4,000kcals for the bike section of an Ironman so an athlete would have to consume between 300 to 750 kcals per hour based on your size, racing experience, training, weather conditions, and food tolerance whilst exercising.

Following a fluid only nutritional strategy would require between 1.3 and 3.2 litres of fluid per hour of competition, if only using the provided fluid option of Gatorade. When we consider what is required to stay hydrated during competition you should be aiming to drink 150-250ml every 15 minutes to offset fluid losses which would equate to only 1 litre of fluid. Now, I’m sure I am not alone in not having a bladder the size of a space-hopper so to effectively fuel on fluids only isn’t looking like a great option if you rely solely and what is available at aid stations.

There is also the potential threat of Hyponatraemia which can come from excessive drinking, firstly, urine production is decreased during excercise which seriously limits the body’s ability to excrete excess fluids and secondly, sodium is lost in sweat making it easier for what sodium is left in the body to become diluted. In milder forms Hyponatraemia causes bloating and nausea, and in more serious cases can lead to headaches, confusion, loss of coordination and even death.

So is it possible to fuel an Ironman on only fluids? Well, yes it is as long as the fluids you are consuming have a higher concentration of calories available. But if you’re reliant on aid stations this will not be the case and a nutritional strategy based upon fluids and performance bars should be employed to ensure you can go the distance.


  1. Hey Karl, just found your blog :)

    I see you're down for the Bustedskin middle distance. Looking at the amount of training you've done since IMUK I'm pretty sure you'll have your revenge (assuming you make sure you get some nuun tabs :P)

    I was out on the road bike for the first time last night. Finally beginning to get my training mojo back :)

  2. Hey Jimbo,

    Good to hear from you, glad your mojo cup is filling up again!

    I don't suffer from cramping as a rule, but I'll definately make sure I have a plan for it - A Nuun delivery truck following me around the course perhaps?!?

    I'll see you down in Weymouth then mate, look forward to racing again.