Valley

Striders

News

Coach's

Column

January 1997

from Club Coach Max Jones

"CARBOHYDRATE LOADING"

In the past four years, Iíve emphasised from time to time - like in every second Coachís Column - the importance of maximising oxygen supply to the working muscles. This Coachís Column is about the other main factor in the energy production equation, the fuel supply, i.e. fat and carbohydrate. Fat need not concern us just now : weíve all got plenty of that, even an emaciated stick-insect such as myself, with around 5% body weight as fat - i.e. 6Ĺ lbs - has enough to run for more than 275 miles and still have some left to get me to Harry Ramsdenís to restock.

Carbohydrate, however, is another matter altogether. Itís very useful stuff because, primarily, it fuels the so-called fast twitch muscle fibres - fat is for slow twitch - and the same volume of oxygen produces 10% more energy from CHO than it does from fat, even though, per gram, fat is worth 9 kilocalories and CHO only 3.75 (say 4 for easier arithmetic, as is the convention used in many articles in the popular running magazines). A 10stone / 140lbs person, male or female, uses 100 kcals/mile and itís 10kcals more or less for every stone / 14lbs either side of 100 (so an 8stone person needs 80kcals for a mile; a 12stone person uses 140cals/mile). But note that energy requirement is weight times distance, i.e. NOT dependant on speed : a 5minute miler and a 10minute miler, each weighing 140 lbs, will each use 100kcals per mile (but because the faster runner travels twice as far as the slower one in the same time, his/her rate of production and usage of energy is, of course, twice as great).

In a table, the sums look like this:

Carbohydrate Requirements

   

60%CHO/40%fat

50%CHO/50%fat

40%CHO/60%fat

Body Weight

Reqd /Mile

/mile

/marathon

/mile

/marathon

/mile

/marathon

8st / 112lbs

80kcals

12g

312g

10g

260g

8g

208g

10st / 140lbs

100kcals

15g

390g

12.5g

325g

10g

260g

12st / 168lbs

120kcals

18g

468g

15g

390g

12g

312g

 

So, obviously, we need to run our marathons, to get our PBs, on 60% CHO / 40% fat, don't we? Answer: no, because the normal store of carbohydrate is only around 300 grams in a person 140lbs or heavier, rather less in a 112lbs person, and the brain, which can only process CHO to keep itself - and you - alive wonít let you run the stock down below 50g or so. So, normally, 60% CHO running cannot be sustained much beyond 15 miles : at or around that point the brain switches you over to 100% fat, your ability to run fast and your will to do so evaporates and you hit the dreaded Wall. You therefore have to choose, before the race, what pace you can sustain - i.e. 50%, 40%, 30% CHO - or you build up your CHO store to enable you to run further faster.

Carbohydrate loading, so-called, entered the marathon racing scene in the 1960s, developed by the manager of the Swedish road-racing team of cyclists (who, in such as the Tour de France, have something like 20 times, i.e. 20 days, the problem that marathon runners have). In its earliest form, as applied to marathoners, the regime consisted of a long fast carbohydrate-using run, such as 20 miles at around 5Ĺ min/mile pace, to UNload the normal reserves so that, in effect, the athletes were told to hit the Wall on the Sunday before the actual marathon race. This was followed by 3 days of very low carbohydrate diet, higher than usual protein and a little more fat, to "tell" the body that there was a race to prepare for, and then 3 days of high carbohydrate diet, lower protein and low fat. Club runners were warned that this process might have undesirable side-effects such as headaches, dizziness, nausea etc etc : it was, in fact, quite dangerous because, as noted earlier, the brain can only process CHO and here it was to be starved of the stuff for three whole days.

Everyone to his or her own taste, but what I do before a marathon is as follows. I train normally - hills, tempo runs, nothing over 16 miles - up to and including the Sunday before the (Sunday) race. Starting Monday and going on through to include Thursdayís breakfast, I eat the same amount of protein as usual but I halve the amount of CHO I eat (and the fat that goes with it) by having 2 spoonsful of muesli instead of 4, one piece of toast instead of two, one potato instead of two etc etc for the 10 meals involved. On the Monday, Tuesday, Wednesday I run 8/10 miles at about marathon race pace : anything much slower than that, e.g. 9 minute miles, uses up much less CHO and thus defeats the object of the exercise. From Monday morning to Thursday morning, I lose about 3lbs in weight, three-quarters of which is water because the CHO is stored as glycogen which is one part glucose, three parts water. On the Thursday morning, being a retired old age pensioner, you realise, I run until I hit the Wall : usually that is 6 or 8 miles, occasionally 10 or 12, once it was only 4. I then spend the next five meals - Thursday lunch through to Friday evening meal - eating a total of about a pound (450g) more CHO than I would normally do - i.e. 4 pieces of toast instead of 2 etc etc - and drinking at least one and a half pints of water at each meal - 30 ounces in American English - to ensure that thereís enough water available inside me to turn the glucose into glycogen. I expect by the Saturday morning to weigh 4lbs more that I did on Thursday (one pound more than on Monday). If itís less than that, I panic and have a spaghetti meal, with water, Saturday evening; if itís more, I go for a brisk 3 mile run to sweat off a pound, otherwise I donít run Friday and Saturday or, apart from a few warm-up strides, on race day.

Since the days of the Swedish cycling team, opinions have swung this way and that on carboloading. The famous Dr David Costill, no less, in charge of the Human Resources Laboratory at one of the State Universities in Indiana, reckons that carboUNloading is unnecessary and itís the two days of eating without running which is important. No one seems to deny, though, that it is impossible to run a fast marathon without some form of carboloading, oneís fat stores being all that is needed for a 5 hour jog/walk over the course. And beware, if your glycogen stores are already depleted by days of fast running, youíll hit the Wall inside the 10k distance and then youíll find it takes a very very long time to walk 20 miles!