Archive for April, 2012
We have previously 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. One of the discussion points was the avoidance of excessive nutrition products during training sessions. Providing a ready source of carbohydrate via sports products can reduce the amount of fat used during training sessions. If you’re using less fat during your training, you’re not allowing your body to practice the fat burning pathway.
This all changes during competition, as your main priority throughout the course is ‘topping up’ the ‘carbohydrate tank’. As previously discussed, the carbohydrate tank is quite small and can run low quickly which would cause you to slow down significantly. In this section, we will presume that you have optimised training and diet for metabolic efficiency. Our main focus during the event and in this section of the guide is optimising carbohydrate intake during competition.
The limitation of carbohydrate intake
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 you throw in there, the amount which can be ferried is limited to a pretty standard 60g. If you take too much, you risk stomach upset due to delayed emptying.
Why is the 60g limit a problem?
Each gram of carbohydrate equates to 4 calories and 60(g) X 4 calories = a maximum absorption of 240 calories per hour. You will utilise anywhere between 500-1000 calories per hour depending upon how hard you are pushing yourself. Initially this calculation may look pretty bad! If you can only absorb 240 calories and you are burning 500-1000 calories, how long before the tank runs dry!! However, it’s not as bad as it sounds. Remember that when exercising you are using both fat and carbohydrate. The 500-1000 calories per hour comes from both fat and carbohydrate and you only need to be concerned about those from carbohydrates.
There are 3 important things to consider:
1. How many calories do I burn per hour?
2. How many of them come from fat?
3. How many of them come from carbohydrate?
You don’t need to worry about the calories coming from fat as your ‘fat tank’ will not run out, that’s why we have encouraged metabolic efficiency from the outset. However, you do need to worry about how many calories are coming from your carbohydrate tank as this has the potential to run out, causing you to slow or stop.
Consider the following example:
A runner or cyclist moving quickly is burning 1000 calories per hour of which 25% come from the carbohydrate tank (25% of 1000 = 250 calories) and the remaining 75% come from the fat tank (75% of 1000 = 750 calories). We know that the body can absorb 240 calories of carbohydrate per hour so if this runner is feeding effectively, he can replace pretty much all of his carbohydrate calories and keep his carbohydrate tank pretty near full.
Unfortunately, runners and cyclists moving quickly are very unlikely to be using fat as a fuel to such a large extent. It’s likely that at higher speeds, no more than 30% of the calories will be sourced from fat, leaving the remaining 70% to come from carbohydrate. This means that the athlete cannot absorb enough carbohydrate to replace what they’ll be using.
What are the consequences of carbohydrate stores running low?
Your carbohydrate tank starts to run low and your blood carbohydrate (sugar) levels will drop, thereby reducing the amount supplied to your muscles. Your body will force you to burn greater amounts of fat to compensate for the drop in your carbohydrate tank, thereby forcing you to slow down.
Things to consider:
- Your fat burning should be optimised beforehand by training and eating effectively, as per sections 1-3 of this guide.
- During the event you should aim to consume 60g of carbohydrate every hour.
- During the event you should avoid going too hard, pacing is critical for fuel conservation!
- 60g is the optimal amount of carbohydrate. Less than 60g is not enough and more than 60g can slow absorption.
Practical application of race day nutrition:
- Carbohydrate drinks are popular, as a simple guide 60g of powder is your supply for 1 hour.
- Carbohydrate gels are also popular and generally contain 20-30g each
- Energy bars are also used and they generally contain 60g each
- If you’re not a fan of sports products, just choose your own foods which are high in carbohydrate.
- For shorter events, carbohydrates which are higher on the glycemic index are best, as they enter the blood quickly. For longer events, the speed of uptake is less critical so glycemic index becomes less important.
- However and whichever foods you choose to take on board, during the actual event you should focus primarily upon high carbohydrate intake and lower fat and protein.
- Ultimately, if you find eating food difficult during longer endurance events, choose any foods which generate an appetite. Irrelevant of sports science knowledge, in longer events, eating ‘anything’ is better than eating nothing.
Questioning the 60g limit
There are lots of sports drinks on the market and pretty much every one of them is the same in content. They mainly consist of a carbohydrate named ‘maltodextrin’ which is a long chain of ‘glucose’ pieces. You’ll see maltodextrin on the side of most commercial sports drinks containers.
The science bit:
Maltodextrin (glucose chain) has always been used for sports drinks and generally always used for research purposes. We spoke earlier about the ‘ferry boats’ which carry carbohydrate across the intestine wall and the fact that they can’t carry more than 60g of carbohydrate, but it may not actually be the case. It may be true that we can only carry 60g of ‘glucose’ across the intestine wall but glucose is not the only carbohydrate.
There are some different ferry boats moored up which are waiting to carry ‘another’ carbohydrate, namely fructose. Because a lot of the early research only used maltodextrin (glucose chain), the 60g of carbohydrate per hour limit might not be true, it may only refer specifically to glucose.
Research suggests that by combining 60g of glucose (as maltodextrin) with 30g of fructose, we may be able to take on board 90g per hour in total. Some commercial sports drinks already combine carbohydrates for this reason.
Great weekend by all accounts and a big thank you to everyone who helped out and everyone who attended. The Saturday evening talks were amongst the best we’d had. First Maxine Grimshaw talked about the ‘middle of the pack perspective’ and her personal experiences of running. This was a great start to the evening, especially when she handed round boxes of chocolates, despite the nutritional advice which had previously been given!! Maxine regularly blogs about her experiences : http://50milesmountainsandme.blogspot.co.uk/ and this was the basis of the talk which was greatly received by all. To follow that, last year’s female winner and course record holder Gaynor Prior discussed the ‘front of the pack perspective’ and how she planned and approached the 2011 event. With strange stories relating to pictures of shoes being posted on the course as motivation and how she fuelled herself with bacon sandwiches, Gaynor gave great insight into the preparation required to break records. Gaynor is a personal trainer based in Leicestershire : http://www.purepersonaltraining.co.uk/ and this year will be marshalling at the event.
There was close to 80 people who attended the guest talks in Ambleside and more than 90 people ran on Sunday. The weather was very kind and although the temperature was a little low at the start of the day, it soon became very warm as runners headed towards Howtown and the first climb of the day. Despite road works, Terry had made his way in the minibus with special permissions to Mardale whilst Clare staffed Kentmere. The finish point for the day was Lakes Runner who provided a free cup of tea/coffee for weary runners and then final weary bodies arrived safe and sound at 6:30pm.
£565 was raised for charity, split between Fix the Fells and Cumbria Air Ambulance, hopefully we will not be calling on the latter during the event in July! The next recce takes place May 13th, covering miles 25-56 of the 100 course, from Buttermere to Dalemain. Guest talks will focus upon navigation, with 2 speakers presenting GPS use and map and compass work. The final recce will then be the double in June, covering the 50 course over 2 days.
Look forwards to seeing you there..
Montane Lakeland 50 & 100