marathon preparation

‘Carbo-loading’ or carbohydrate loading is a phrase that most runners will have heard of and for a lot of novice runners this may translate as a pasta party the night before your race. Have you ever really considered exactly why it is so important to load up on complex carbohydrates before a long distance run? While loading up on carbohydrates beyond your normal dietary intake does not appear to impact upon performance in events lasting up to 60-90 minutes; in longer distance events like a marathon, maximising your energy stores has been shown to have a big impact on your performance. I’m sure you’re familiar with the concept of hitting the wall – this is essentially your body exhausting its carbohydrate reserves.

The Science of Why

We need to look at the numbers to understand why carbo-loading is so essential for marathon preparation. In our bodies, we store limited amounts of glycogen (or carbohydrates) in three places: in our liver, our muscles and in our blood plasma. Our total carbohydrate reserve is insufficient to fuel a marathon as blood plasma typically stores less than 20kCal, our liver typically 350kCal and our leg muscles 1250kCal. Our total typical reserves of glycogen then equal 1620kCal with the additional limitation of only being able to use the glycogen stored locally in a muscle to fuel that muscle alone. How many calories do we burn typically in a marathon? A little under 3000kCal. We can see that the fuel cost of running a marathon far exceeds our fuel stores. We can’t expect therefore to jog up to the starting line without some sort of preparation.

The Recommendations for How

Training Phase
By the time race day arrives, you will have completed several months of consistent training including a lot of long, slow distances. This will have a big impact on how your body burns fuel on the day, delaying the anaerobic threshold where the body starts to really use up its limited stores of glycogen. What is used before this? Fat; of which, our bodies typically store enough to fuel us through nearly 600 miles. Even the leanest of long distance athletes have enough fat stored to fuel back-to-back marathons! The only issue is that race pace is faster and more intense than training pace, meaning that we do have to dip into our glycogen stores as we are pushing our bodies harder.

Week Before
In the week before Race Day, it is important to increase our intake of complex carbohydrates to boost the local storage of glycogen in our leg muscles.

Examples of high carbohydrate, high glucose foods include:
• Pasta • Bread • Rice • Potatoes

Leaving it until the night before to bulk up on carbs will just leave you feeling heavy and bloated and will certainly not boost your energy levels the following day. Our general diet should contain anything between 3-7g of carbohydrates per kilogramme of body weight. To bulk your carbohydrate intake this should be increased to about 10g per kilo of body weight for the 36-48 hours before race day.

Race Day

On race day, it is essential to consume carbohydrates that can be easily and quickly absorbed into your system for immediate use and fuelling. By consuming easy carbs on the day, you will maintain your glycogen stores for longer allowing you to tap into those reserves when you really need them.

Examples of carbs you can consume on the day and during the race include:
• Carbohydrate-electrolyte drinks • Sports gels • Energy beans and bars

It is recommended to consume 30 – 60g of carbohydrates every hour and intake should be at least 30min before you anticipate fatigue onset. You should ideally be taking on fuel regularly from 60-90 minutes into your run. Another piece of advice – do not try anything for the first time on the day! Nausea, cramping and stomach upsets are not issues you want to have to deal with when you are 20 miles into the run. Whatever source of fuel you choose to use in the marathon you should have tested it out on one of your long runs during training beforehand.

by Chartered Physiotherapist Sarah Liddane

Our chartered physiotherapists and personal trainers are fully trained in giving you advice on how to approach your marathon and are passionate in helping you achieve your running goals. To schedule an appointment please call us 01 531 0007

References: IAAF Medical Manual, [online] Available at: