Only a week to to go before the big day! PLEASE have a look at my JustGiving page for the charity I am supporting. Genie’s Wish really deserves the donations, so they can improve the lives of people with terminal and live limiting illnesses. Thank you so much, Nick xxx
Fuel the Machine
Riding for 24 hours is as much an eating competition as a bike race. When a machine runs out of fuel, it stops.
The challenge is to be able to put out an effort, while still taking in carbs and burning fat, without emptying the body’s energy stores. This is a tricky balance to strike and I’m lucky to have been helped with some testing at Loughborough Uni.
First, it’s important to understand the way muscles use both fat and carbohydrate for fuel.
Even in a lean person, fat stores are effectively limitless in a 24-hour event. Just 7kg of body fat contains 63,000 kCal : enough to ride more than 1,500 miles without eating.
Sadly, fat has two major limitations.
First, fat stores can only be burned quite slowly. In me, this peaks at about 48g/hr. This releases 430 kCal, enough to produce about 125w of power on the bike (the body is about 25% efficient at converting food energy into mechanical work).
Second, fat-burning drops off when exercise gets more than moderately hard. My fat-burning peaks when I’m riding at about 215w (70% of threshold power). By the time I reach threshold, fat-burning is effectively zero.
In contrast, carbs burn faster, but also have much smaller stores. In my test at Loughborough, I could burn about 265g carbs per hour at threshold, enough to produce about 310w on the bike.
The problem is that using carbs at this rate will burn through the body’s stores very quickly. The 500g of glycogen stored in the liver and muscles contains only 2,000 kCal – enough to ride about 50-60 miles.
Fortunately, consuming carbs during exercise can make the stores last longer. Typically, we can absorb up to 90g/hr of carbs, but only when the conditions are perfect: low-to-moderate exercise intensity, the right combination of foods*, adequate hydration, and little fat or protein in the diet.
*The composition of carbs ingested is also important. Glucose and fructose are absorbed from the gut through different transporters at a ratio of 2:1. To make the most of both routes, food should ideally contain 2g glucose (or glucose polymers such as starch or maltodextrin) per 1g fructose.
So what does this mean in practice? For a short event like a 10 or 25 mile time trial, it hardly matters. The intensity is so high that fat-burning is near-zero while the duration is short enough that glycogen stores will last the distance, even without consuming anything.
But for a 24-hour ride the opposite is true. Carb stores alone can only fuel 50 miles of riding, so carb intake and fat burning are crucial. For me, riding at around 200w, fat burning can supply about half the energy I need, but I still need to make sure I’m keeping the carb stores topped up. If I don’t eat enough, or if my gut slows down, it won’t be long before the reserves run out and the man with the big hammer comes along.
Putting it Together
So after a lot of trial and error, and applying the results from Loughborough, here’s my tested plan:
- ride a steady 190-205w Normalised Power (65%FTP)
- keep the effort easy at all times (HR always <145)
- avoid power surges (power always <275w)
- for 2 days before the event, eat 8g/kg carbs per day, with low-fat, low-fibre foods (eg rice & pasta), generous salt, and plenty of water
- on the morning of the event, eat breakfast 3-4 hours before the start, with 120-150g carbs, some protein and just a little fat (eg rice and 2 poached eggs)
Food during event
- eat or drink some carbs every 15 mins
- consume 90g/hr carbs if possible, 60g/hr minimum
- take a combination of energy drink, sports bars and savoury snacks to give a 2:1 ratio of glucose:fructose
- minimise fat and protein intake while riding
Water during event
- consume enough water (about 500ml/hr) to need a decent pee once per 2 hrs
Sodium during event
- consume 500-750mg/hr sodium per hour (eg 2xHigh5 electrolyte tabs in drink + 1x salty snack)
- If drinking more than 500ml/hr, take extra sodium (approx 1000mg per extra litre drunk)
Will it work? I suppose we’ll find out next weekend!