Using your power meter to track your calorie burn on the bike

Anyone who has ever run out of energy on a long ride will know the agony of bonking or getting the knock. Here’s how you can use your cycling power meter to measure energy expenditure and make sure you get home without hitting the wall.

Anyone who has ever run out of energy on a long ride will know the agony of ‘bonking’ or getting the ‘knock’. It’s quite hard to describe the knock if you’ve never experienced it, but you only need to experience it once to know exactly what it is. Depleting your body’s energy stores almost to zero through inadequate re-fuelling will have you wanting to roll off the bike and go to sleep at the roadside. If you’re 40 miles from home with no way of accessing some additional supplies then it can be a thoroughly gruelling experience.

Here’s how you can use your power meter to measure energy expenditure and make sure you get home without hitting the wall.

Avoiding running totally out of energy on the bike is really to be avoided at all costs. But for most of us who lack the support of nutritionists, stagieres and team cars it is something that can only really be avoided by adequate ride planning. You’ll either need to ensure that you have sufficient nutrition on hand before you set off, or at the very least have included some café stops on the ride where you can pick up your favourite snacks to re-fuel.

But what about those occasions where you don’t plan your fuelling strategy. Or you do plan your fuelling strategy but feel so good on the day that you decide to throw an extra 30 miles onto the ride? One lesser used benefit of riding with a cycling power meter is the ability to effectively track how many calories you are burning as you ride. If you have some idea of your average watts over a given duration then through some simple maths you can figure out what you need to consume to avoid going too far into the reserves.

So how do you go about turning the watts recorded by your power meter into Kcal? The maths is actually quite straightforward:

Energy (kcal) = Average Power (W) X Duration (Hours) X 3.6

To calculate energy expenditure, you simply multiply your average power by duration, with 1 Joule being 1 Watt of energy for 1 Second. A sustained average power output of 100W for an hour (3600 seconds) is therefore 360,000 joules, or 360kJ. The 3.6 constant is included above since to turn calories or Joules into Kcal we must divide by 1000, and as we are measuring over an hour we get 3600 seconds/1000 = 3.6.

We humans are however not perfectly efficient, and in actual fact the human body burns about 4 Joules of Energy to deliver 1 Joule of Energy to the pedals. So for every Joule measured we need to increase that figure by a factor of 4 to approximate the calories burned. However, because a calorie is roughly 4 Joules we can decide to ignore this fact and can say somewhat roughly that measured Joules is equal to Calories expended.

Plugging our numbers into the equation and bearing in mind the aforementioned, we see that:

100W X 1h X 3.6 = 360kcal

So, now you can use your cycling power meter (and possibly your smartphone calculator!) to calculate roughly the calories you are burning as you ride along. If you know your average power for a given duration then simply multiply that number by the duration expressed as a fraction of 1 hour, and then multiply that figure by 3.6. To keep things simple, you find nowadays that many head units will very handily provide a Kilojoules figure as you ride.

So, what does this mean to anyone with a cycling power meter? Firstly, this calculation helps greatly with ride planning. If you know how much power you plan to generate whilst you are riding then you can formulate your re-fuelling strategy accordingly.

If you’re generating 200W on average for an hour, and you’re going on a 3 hour ride, then you know you’re going to burn through around 2200 kcal. That’s around 22 apples or 8 chocolate bars. Eat less than this and you will enter a calorie deficit where you start to call on your body’s fat reserves to keep going.

As we have seen you can of course also use this simple calculation to keep track of your energy expenditure as you ride, which is important if you have run out of food or plan to pick some up along the way.

You can start to see at this point exactly why adequate refuelling is essential for success at the elite level. Riding an event like the Tour De France requires on some days upwards of 5 hours in the saddle riding at our around race pace throughout that time. It would not be uncommon for riders to burn 5,000 to 6,000 calories per day, which is around 120,000 calories over the race.

One pound of body-fat contains around 3,500 calories, so that’s enough energy to burn through around 35 pounds of body fat over the 3 weeks, an astonishing amount. However, the body fat levels of the modern elite cyclists are very low and so all energy must be derived from carbohydrate, which basically entails continuous consumption of food throughout the stage.

So now you can use your cycling power meter a little more broadly, but all of the aforementioned is of course prefaced on accurate data. If you have an inaccurate cycling power meter not only do you not know what your power output is, by extension you do not know how much energy you are expending.

The former can be disastrous for training as you don’t know how hard you are trying, and the latter can be disastrous when you run out of food and energy 20 miles from your destination and have to grovel back pedalling in squares. As the only cycling power meter that lives up to its claims of accuracy, the InfoCrank is therefore a must have for any cyclist serious about his or her pastime.

As our knowledge of cycling increases, we have seen that cycling power meters have become indispensable not only at the top echelons of the sport but also for recreational cyclists who want to get more out of themselves and their passion.

Cycling power meters can be used for much more than recording power output, and truly accurate power meters like the InfoCrank can provide data that is indispensable for tracking your physiological processes and progress and ultimately helping you do more of what you enjoy. By equipping yourself with an InfoCrank you can be confident you have the best tool to train properly, re-fuel properly and achieve your fitness goals on the bike no matter what they are.

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