Probably the most misunderstood aspects of racing long course is fuelling the race itself.

My aim with this post is to keep it as simple as possible and truly it should be !

Key Factors :

Your Fuel Tank :

Most athletes will have a fuel tank resembling 300-350g thats useable muscle glycogen. You body stores it in other areas also of course such as the in the blood, the brain and the liver but we are talking muscle glycogen here that can be converted to energy and used to push us forward.

Your Glycogen Combustion Rate :

Just like your car, it depends on how fast you are going.

For a 70.3 that ranges from 0.75 to 0.85 of your FTP. This is called your intensity factor or IF if you look it up in Training Peaks sessions.

Let’s use 0.8IF and the combustion rate we get from that.

There is a definite range here as it will depend on your individual metabolic profile.

If you have been doing endurance sport for a while you will most likely, at 80% intensity factor, burn around 120g of carbohydrate per hour.

*Screen shot from an INSYCD test performed on our example athlete*

Your Finish Point of Your Race :

You do not want to finish your race on fumes, having zero in the tank.

Your aim is to finish with around 100-150g in the tank

Your Fuelling Window :

If you are doing a 4:30 race as I will outline below you haven’t got that time to fuel. In fact, if you come out of the water in around 30min, transition, and then settle in on the bike it may be around 40min before you first onboard carbs.

Then take off 15min at the end of the race as the last point where you are topping up with carbs that can be used.

This leaves 3:45 as your fuelling window

An Example Race Nutrition Model :

Fuel needs :

4.5 hours at 120g / hour burn rate (we will assume the same burn rate across the race)

= 540g needed

—---

Stored fuel :

350g tank

150g left in tank at end

= 200g carbs available (endogenous glycogen)

——-

Fuel to be consumed :

540g needed

200g coming from stores

= 340g carbs needed (exogenous glycogen)

Remember !

Absorption is limited by the gut : Typically you can use

~60 g/h for glucose only
~90–120 g/h for multiple transportable carbs (e.g., glucose + fructose)

——

The Fueling Window :

340g need to be taken on board

3.75 hour fuelling window

= 90g/hour

That’s quite a bit and if you don’t / can’t fuel at that rate you will have to slow down.

For our example athlete shown above, going down to 75% Intensity Factor (a 15w decrease) means now burning carbs at 95g/hour. A 25g/hour saving.

However, remember that whilst a 15w decrease reduces your burn rate by 25 per hour a 15w over-shoot in power will cost you 25-30g per hour more fuel. A challenge that is unlikely to work out well and leave you finishing very slowly.

Considerations :

A Full Tank on the Start Line :

The 350g fuel tank relies on a carb load the day prior at 8-10g/kg/hr to super saturate stores. Reduce fibre and keep the carbs simple.

Overnight, the body shifts toward fat metabolism, but liver glycogen is depleted to maintain blood glucose.

So a breakfast top-up is important to top up liver glycogen although muscle glycogen isn’t significantly depleted overnight unless fasted or glycogen-depleted the day before.

The Bike / Run Breakdown :

If you struggle on-boarding carbs while running you might like to consider having slightly more on the bike and less on the run. This will also help you have as full a tank as possible to start the run, allowing you the best opportunity to perform at your best.

Logistics :

Where do you store all this ? Gels are great. So is having some carb powder in your hydration. A mix of both can be good for those that hate gels and want keep them to a minimum. This can be a drama to carry more powder however and empty it into your water bottle when you need a top up.

Hydration / Electrolytes :

A key factor in a nutrition plan but a topic for another day. At this point in time aim for 500-750mg per hour of electrolytes and 750ml per hour of water. We can discuss from there.

Common errors :

Not practicing your model in training
Not learning from previous races (either bonking or having gastric distress)
Make sure you test yoru model and know you can process carbs at the levels you have need.
Thinking more carbs will make you faster - Adding fuel to your car doesn’t make you faster, it allows you to last longer at your correct pacing.

Recommendations :

If I was racing I would separate carbs from electrolytes as if it’s a hot race you can get thirsty and end up drinking too many carbs
I would have electrolyte tablets for the water bottles and I would use a combination of gels and chews for carbs.
Test test test. In training, race power and pace, at race like temps if possible, using the brands you will use on the day.

Fuelling a 70.3