By Daniel Brayson, King’s College London, @DrDanBrayson
In cycling very long distances as fast as possible, ultra-endurance cyclists use an extraordinary amount of energy. Replenishing these energy stores is critical for racers to maintain performance and stay competitive. To achieve this, riders do not simply settle for 3 square meals per day, or even 3 big meals a day, which would simply not be enough! Instead, we eat more frequently, and because we do not want to stop too often, this means eating whilst riding: “grazing on the go,” as it is affectionately referred to amongst cyclists. This involves eating an array of convenient snacks ranging from the healthy – bananas, oranges and kiwi fuits – to the energy packed goodness of carbohydrate and fibre rich wholegrain bars, nuts for fat replenishment, all the way through to the downright despicable: chocolate bars, Peperami and lots of jelly sweets. Did I mention ice cream? There was a bit of that too. The overriding consensus amongst riders is that a calorie is a calorie no matter where it comes from, and you take all you can get!
Biting more than you can use
Although it is intuitive to think that you need to eat a lot more to compete in these races, there is a limit to how much energy a human can take on board. Take the example of carbohydrates. The limit to how much carbohydrate can enter the bloodstream is dictated by a clever transporter system between our gut and our circulation. The ‘problem’ with this system, from the point of view of an ultra-racer, is that it can only transfer approximately 60 grams of carbs per hour from the gut to the bloodstream, maybe up to 90 at a push. In an ultra event, racers are likely to use much more. On top of this, this transport relies on an adequate blood supply to the gut to deliver energy to the system and facilitate it’s function. However, when cycling most of our blood supply is directed to the muscles because they are using so much energy. This can make this transport system slower and less effective and may lead to “gastrointestinal distress” – tummy ache to you and me! This is a common problem for ultra-cyclists, but it is even more common in ultra-runners, probably because of there is more jumbling up and down in the tummy, which I think is the technical terminology…
Measuring the loss of energy stores
If the human body is in a state where it can’t take on as much energy as it uses, it is likely there will be a net loss of energy stores in the body; this has actually been shown in a couple of studies which examined ultra cyclists. However, the magnitude of this deficit is up for debate. One study showed that it could be as much as 8000 calories per day, whilst another derived that it was a more conservative 1500 calories. This discrepancy is likely due to the fact that these studies chose very different methods of measurement. To add to these studies I attempted to use yet another type of measurement to see if I could determine my ‘energy status’ during the Transcontinental Race. I opted for measuring circulating glucose (sugar) and lipids (fats) by pricking my finger and then using an everyday device that a diabetic might use to monitor their blood sugar. Simple.
Or perhaps not. I found that when I measured glucose, cholesterol and triglycerides, values were usually either the same as or higher than the resting values that I measured before the race, which goes against the hypothesis that I would be suffering from an energy deficit, and the data generated by previous studies. I can think of a number of mitigating circumstances. Firstly, I had devised a plan to take measurements pre- and post-meal. Yet, it quickly became obvious that I would rarely find myself in a pre- or post-meal state, because I ate so often. Timing of measurements was therefore erratic at best. Also, continually lancing my fingertips became a painful burden: my fingers were wounded and bruised for most of the time I was racing. Eventually, I decided it was too much of a hindrance, especially as my chances of finishing the race were already jeopardised by heat-induced illness. Heat also affected my appetite and ability to adequately digest: I was nearly re-acquainted with more than one meal towards the end of the race and spent the last two days eating nothing but ice-lollies.
In case you needed reminding, this was no walk in the park! Come back next week to find out if the ice-lollies got me over the line!
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