In recent articles, we’ve discussed the 2 main fuel sources for endurance exercise (fat and carbohydrate) and how you should optimise your body to burn fat, thereby allowing you to save precious carbohydrate stores. When it comes to race day then the game and the rules change completely. As a recap, when training you should:

1. Ride or run at the correct intensity or follow a specific protocol such as Maffetone
2. Avoid fluctuations in intensity, remember that average heart rate or power output are NOT the critical figures, it’s TIME IN ZONE that counts
3. Eat foods which are balanced with low GI carbohydrates and fats to encourage fat usage and avoid sugar spikes
4. Avoid gels and sugar products based on point 3 above

If you follow the above guidance, over a 12-16 week training period, you can teach your body to utilise a greater amount of fat as fuel and also to use less calories overall, making you more economical. The important thing to remember is that ‘training’ and ‘racing’ are 2 separate things and your fuelling approach should reflect this.

What happens during the race?

Okay, let’s presume that you have trained correctly and maximised your fat burning potential and fuel economy. You reach the first event of the year and when riding or running at race pace you are using 700kcal per hour, 50% of which comes from carbohydrate and 50% of which comes from fat. You only need to worry about the carbohydrate loss as that’s the one which is critical, so let’s focus on the 350kcal of carbohydrate which equates to 88 grams of carbohydrate (4 kcal per gram).

The limitation of carbohydrate intake

Here’s the big problem, you can only absorb approximately 60g of carbohydrate per hour. Imagine that there are small boats, which ‘ferry’ carbohydrate across the intestine wall into your blood stream. Unfortunately you only have so many ‘ferry boats’ so no matter how much carbohydrate you throw in there, the amount which can be ferried is limited to a pretty standard 60g. For our example above, that means that you’re going to fall short. You’re using 88 grams per hour and you can only replace 60 grams per hour. That’s a 28 gram / 112 kcal per hour deficit.

So I can’t just eat more?

Unfortunately not. If you eat more, it’s unlikely to be digested and will simply sit in your stomach or intestines without providing energy. There are a lot of people who suffer from gastric problems during long distance events and this is generally caused by eating too much food which they are unable to digest. It’s really important that you understand, eating more food doesn’t mean you’ll have more energy and it may well mean that you’ll face stomach upsets. I stress this point knowing how obsessed Ironman athletes in particular become with regards to feeding on the bike.

A deficit of 112 Kcal per hour doesn’t sound too bad

No, it doesn’t. But that is based on the presumption that you are only using 700kcal per hour, bigger people and less efficient people may be using more. It’s also based on the assumption that 50% is coming from fat and that may not be the case at all, in fact, as much as 80-100% may be coming from carbohydrate. What makes this worse is that bigger people can’t necessarily take on board more fuel, the 60g limit still pretty much applies. It’s a gut issue, it’s not about how big your muscles are and how much you can store in there.

So the 3 things you might want to know are:

1. How many calories do I burn per hour?
2. How many of them come from fat and carbohydrate?
3. How much should I be taking in as a consequence?

As a start point, you can probably work out your calorie usage by using a heart rate monitor or power meter. Run or ride at race pace and it’ll do the calculation for you, although the power meter is a lot more accurate than the heart rate monitor, it’s still a start point. Warm up, then do an hour at your ‘race pace’ and work out the figures. It’s amazing how many people who consider their training and racing to be ‘serious’, still have no clue how many kcal they use when racing. How can you have any grasp of nutrition requirements without knowing this figure? Once you’ve calculated that figure, apply the following rule:

80/20: If you are struggling to ride 50 miles / run 15 miles even when fuelling yourself throughout, then apply the 80/20 rule. That means 80% of your fuel is carbohydrate and 20% is fat.

65/35: If you can ride 50 miles / run 15 miles comfortably using fuel, then apply the 65/35 rule. That means 65% of your fuel is carbohydrate and 20% is fat.

50/50: If you can ride 50 miles / run 15 miles comfortably without using any fuel whatsoever, then apply the 50/50 rule. That means 50% of your fuel is carbohydrate and 50% is fat.

Are those figures accurate?

Absolutely not, I just made them up. They are by no means 100% accurate but they will give you a good start point and will allow you to calculate an approximate figure. The running figures are less ‘straight forwards’ than the cycling, as the impact of running can really fatigue your legs, so you may find 15 miles difficult, even if your fat burning and fuel economy is good. for cycling, the impact is low, so it’s more likely governed by metabolism and fuel.

Ok, so what’s the next step?

Here’s what we’re going to do. Prior to next week you are going to do a 1 hour ride or run at your ‘race pace’ and then using your cycle power meter, GPS or heart rate monitor, calculate how many calories per hour you are using when exercising at that intensity. I feel this is a pretty important thing for you to understand if you are to race successfully. It’s easy with a power meter for cycling, it does the maths for you. Most heart rate monitors will use your age and weight to work out kcal per hour. There are some tools on the internet such as: http://www.braydenwm.com/calburn.htm which can help to give you a basic idea.

Go forwards my endurance friends and do the maths, next week, we will be looking at planning your intake.

Until then, stay healthy.

– Marc Laithwaite

About Marc:

Sports Science lecturer for 10 years at St Helens HE College.

2004 established The Endurance Coach LTD sports science and coaching business. Worked with British Cycling as physiology support 2008-2008. Previous Triathlon England Regional Academy Head Coach, North West.

In 2006 established Epic Events Management LTD. Now one of the largest event companies in the NW, organising a range of triathlon, swimming and cycling events. EPIC EVENTS also encompasses Montane Trail 26 and Petzl Night Runner events.

In 2010 established Montane Lakeland 50 & 100 LTD. This has now become the UKs leading ultra distance trail running event.

In 2010 established The Endurance Store triathlon, trail running and open water swimming store. Based in Appley Bridge, Wigan, we are the North West’s community store, organising and supporting local athletes and local events.

Check out the endurance store HERE