Is doesn’t take a biochemist to know that carbohydrates are the MVP when it comes to fuelling high intensity exercise. But how much do we really need, and how do we know we’re putting in the right stuff?
Our body has three main fuels to produce the energy required for the thousands of muscle contractions during an endurance sporting event. Carbohydrates are used predominantly when the pace is on, fats when the intensity is lower and once the carbs are gone and there’s less fat available the body will start burning muscle protein as a last resort.
In a high intensity event such as a bike race, where bursts of power could be required at any moment, readily available blood glucose is essential throughout a race to maximise performance. Endurance training prior to an event increases the mitochondria content in adipose tissue, essentially allowing greater energy production from fat sources over carbs. However, despite this being convenient for shedding some kg’s, fat oxidation is a much slower producer of energy than carbohydrate oxidation. Trying to race well off purely fat stores would be the equivalent of running a formula 1 car on diesel, the mileage may be better, but you’d be left behind easier than a phone charger in a hotel room.
We’ve established that we need carbs to go fast, but how many for a long race?
Quick answer: a lot.
Long answer: Carbohydrates ingested during a race aren’t the only ones that go into turning the pedals around, with glycogen stores in the muscles and liver playing an essential support role however one that will be addressed in a post in depth at a later date… To get an idea of how much to put in, first we need to calculate how much is going out (physicists get excited).
Say in a hard race a cyclist averages 292 watts (you’ll see why this number shortly…). The average power output on a bike is simply the total energy put into the pedals divided by the time taken to do it. In order to work backwards and find the energy spent the average watts are multiplied by the total seconds. So cycling at 292 watts for an hour (3600 seconds) requires 1,051,200 joules of energy (1051kJ more commonly). Unfortunately, our bodies aren’t 100% efficient, and only around a quarter of the energy spent by the body ends up making it into the pedals, with most lost as heat. This means that 1051kJ of energy into the pedals each hour requires about 4200kJ. Because we still haven’t made it to the metric system for measuring the energy in food that equates to a whopping 1000Cal per hour. A seven-hour race like the Melbourne to Warrnambool would therefore require more than twice the recommended daily calorie intake during the race to put in the same amount of energy that’s put out.
In terms of carbohydrates that 1000Cal per hour equates to around 250g of carbohydrate or 10 bananas. Before you go packing 70 bananas in your pocket it’s important to remember that carbohydrate isn’t the only fuel source during a bike race. A race with someone achieving a normalised power around 80% of their threshold will result in carbohydrates and fats providing close to an even share of the fuel supply. In the example above that would still require around 125g of carbs per hour, fortunately glycogen stores exist.
The task of putting in the same amount as you put out is made even harder by the fact that most people can only metabolise between 30-60g of carbohydrates per hour. Trained endurance athletes have been shown to reach 90g/h of carbohydrate metabolism but unfortunately this can’t be achieved as simply as shovelling down three or four muesli bars each hour.
To maximise absorption of carbohydrates in the gut it’s important to pay attention to which specific carbohydrates are put in. As one might expect, sugars are going to make their way into the bloodstream faster than complex carbohydrates, but there’s a few other tricks that can be used to max that carb absorption. Sugars make their way across the gut wall via a range of different specific transporters. The transporters can be thought of as gates that only let through their favourite sugars. If a mountain of glucose is poured into the system there’s only a certain few that can get through the gates into the blood at any time. But if some extra fructose is added then these have some unused gates to waltz through and get into the bloodstream, increasing the total carbohydrate absorption. (Before the biochemists send in the hate mail, it’s not quite this simple, with a bit more competition and a few more steps in the process but the principle is the same.)
Studies have found that for maximum absorption a ratio of 0.7:1 of fructose to glucose is best. Rather than weighing up the ratios of apples to jelly beans during a race this is usually achieved with a pre-made drink mix. Increasing the absorption rate of carbohydrates in the gut by nailing these ratios doesn’t just help keep the blood-glucose at optimal levels but also allows for better fluid absorption and causes the gut to empty faster, preventing the bloating or discomfort riders often face when trying to stuff their faces with carbs mid-race.
With all this in mind, eating during a race can seem a lot harder than trying to rip the top off a gel without ending up with half of it on your top tube. Fortunately, our bodies are pretty good at keeping us going, particularly with training, and there are many other adaptions that help give those muscles their sugar hit when chasing those last few attacks. Well-planned carbohydrate loading and training the body to prioritise fat burning where possible allow endurance athletes to always have that little extra ready to go when they need it however good fuelling during the race is always important.
For races where you really want to be firing at the end (most I hope) try to get in around 60-90g per hour at a ratio of 0.7:1 fructose to glucose and you’re on the right track. Most importantly, work out what works best for you. It’s not always possible to smash 4 gels an hour and most people just prefer solid food so give a few different combos a try during some long training days and settle on a nutrition plan you can back in to have you feeling good and going fast.
This topic had a lot to fit in, (fitting given the content) and ate into my Warrnie prep more than expected. Having loaded up on carbs the last few days and after a lot of fasted training to promote fat oxidation I’m confident I’ll be able to keep the blood sugar up throughout the race tomorrow. I won’t quite be aiming for the 90g/h mark on carb intake and given I’m racing solo with no team support I’ll be making do with whatever I can find out on the road in terms of bidons. Buying some fancy gels and drink mix would exceed my yearly salary of $0 so it will be a good chance to burn through all the leftover gels I’ve somehow accumulated over the past 12 months of racing. Hopefully they’ve got the sugar ratios I’m after and I can come home with some chocolates. Until then, I’ll keep reading the research papers so you can spend more time on the bike.
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