Thanks again to the poster who answered my query about nutrition. Now I'm training at the 13-mile stage, it's time to start introducing carbs along with the fluids. Mind you, the post did warn about the 'trots' - and that's led me to a scary new field of research.

I started with the sports nutrion advice on the Flora London Marathon site. And please excuse me if my excerpts from the basics are too basic for you. But this is my first marathon and I'm beginning to discover just how much there is to preparing my system for battle.

Under The Basics comes the clear advice:

"The loss of fluid and a reduction in the body’s carbohydrate stores are the two major causes of fatigue in prolonged exercise."

The following goes with the graph:

"Above is a heart rate trace of an endurance runner completing a marathon. This demonstrates the premature onset of fatigue, commonly known as ‘hitting the wall’.
Miles 1 – 18: even paced running (5.35 min/mile). Steady HR at 90% of maximum
Miles 18 – 26: a gradual decrease in pace from 5.35 to 6.35 min/mile
Final mile was completed in 8.40 min/mile."
 

Carbohydrates are stored as glycogen - a sort of fuel. The advice continues:

"Fatigue occurs when glycogen stores are depleted resulting in significant reduction in running speed. Crossing the start line with already low glycogen stores is like taking a car out with a half empty fuel tank – you will run out of fuel more quickly and may suffer premature fatigue."

So what do I have to do? In terms of my daily diet, I have to up my carbohydrate intake from 40 to 50 per cent of my intake to 60 per cent. Mind you I enjoy pasta, rice, porridge and potatoes - so that's no problem - not when my Garmin training program says I'm burning the best part of 2,000 calories on the two-hour runs.

But what about the long run? Under Preparation is the following (and bear in mind that Lucozade is a London Marathon sponsor) :

" 20 mile ‘easy’ run. Drink 125-250ml of Lucozade Sport at 5, 10 and 15 miles. This does depend on what you can stomach, but this is good information to find out now! You may also want to practice using a Lucozade Sport Carbo Gel at 15 miles, taken with 150ml water or sports drink."

The phrases "what you can stomach" and "want to practice" give a hint of possible problems.

I divert to The Teach Yourself book "How To Run A Marathon" by Tim Rogers (also see my post "Mixing up the training")  for the following:

"Many weeks beforehand you should find out the particular brand of energy drink that your event is using on race day and train with it. They are all different and you must make sure that your body is used to the specific brand available at your race. Do not train with one and then use another on race day or you could face some significant stomach problems."

And I thought I'd just "hit the wall" if I got nutrition and hydration wrong!

All advice extremely welcome.

* Training note: 12.85 miles round Hanningfield reservoir at an average 8:52 per mile. And to the driver pulling faces at me near the Windmill pub, please see my post about the Highway Code and pedestrians facing oncoming traffic on lanes without pavements. My hand gesture was merely an attempt to refer you to clause two...

I'm running for the Great Ormond Street Hospital Children's Charity and you can sponsor me here.