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How to Unlock Your Performance and Energy Levels by Analysing your Breath

Lumen is a ground-breaking portable device that, through a breath, tells you what source of fuel your body is using to produce energy. Previously hard-to-access data is now available to anyone.

Every athlete needs energy to perform. The ability to walk, run, lift weights and, on a more basic level, sustain every bodily function, depends on one’s ability to extract energy from the food we consume.

This energy comes from primarily two sources: fats and carbs. Your body’s ability to turn this fuel into energy, a process known as metabolism, is a key determinant of exercise performance. Depending on what exercise you’re doing, whether that’s a walk in the park, some yoga or a long CrossFit® session, you will need to access different energy sources.

On a basic level, it’s only possible to use fat for energy when the intensity of the exercise is low enough so you can deliver oxygen to your muscles at the rate required. As your intensity goes up, and you require more energy each minute, the proportion of energy that’s coming from fat comes down and that of carbs goes up.

When you’re doing a high-intensity WOD for example, fuel comes from mostly carbohydrates because the energy you require needs to be created at a very fast rate.

Knowing what source of fuel your body is burning for energy at any given time can be an invaluable piece of information for athletes, and Lumen can give you this knowledge.

With the data acquired from measuring your respiratory exchange ratio (RER), which establishes whether you’re using fats or carbs for fuel, you can train your body to become better at shifting between energy sources and to tap into different stores according to your needs – think of it as metabolic flexibility.

So how does this actually work and how is it applied to CrossFit®?


Knowing what kind of fuel you’re burning in the leadup to a workout can be the difference between an average session and an successful one. Simply put, if your carb stores are low (which means you’re burning mainly fat), you won’t be able to deliver oxygen to your muscles at a fast enough rate to create the energy that the exercise demands.

Lumen is a ground-breaking device that tells you whether you’re burning carbs or fats for fuel, on the spot. This information provides exciting data that you, as an athlete, can then act upon.

When you start with Lumen, you can choose for it to use the data to either lead you through healthy weight loss, improving your metabolism and building good habits, or optimising nutrition to support workouts and improve performance. I’m using Lumen as a way to improve my performance.

lumen metabolism breathe

This means that, every time I breathe into Lumen, it uses the data acquired to optimise my nutrition and make sure I have enough energy for my upcoming workouts. As Lumen’s AI gets to know me, it also learns how my body reacts to specific exercise, and offers nutritional recommendations based on that.

Establishing whether your body is burning carbs or fat for fuel is solid science and is calculated by measuring an individual’s respiratory exchange ratio (RER). This is the ratio between CO2 produced in metabolism and oxygen used.

Lumen calculates this ratio based on the RER metric by measuring the CO2 concentration in a single breath. You breathe a fixed volume of air (dynamic to each individual) through the device, hold it for 10 seconds and exhale fully. Lumen then analyses your breath and tells you your metabolic fuel usage.


I “unlock my day” by breathing into Lumen every morning – I’ve been using the device for close to a month now. I also get a reading every time before I exercise, log the type and duration of my exercise, and use Lumen again afterwards. I do the same before and after for meals, so I can see how my carb stores change after specific meals (or a specific number of carb servings).

metabolic flexibility lumen

My readings before workouts have varied between ones and twos (burning mostly fats), threes (burning both fats and carbs) and fours (burning mostly carbs). Having this insight has proven to be highly beneficial, and I can act on it.

My energy levels during my CrossFit® workouts have been higher than usual because I can ensure I’m fuelled adequately for each and every one of them.

By using Lumen after a workout, I can learn what impact different intensities have on my systems. Starting a workout on a Lumen score of three (burning both fats and carbs for energy) and finishing on a two (burning mostly fats) means I used my carb stores on that exercise, but I probably wouldn’t have been better off having started with higher carb stores, as I still had some carbs left.

metabolism measure
Measure your metabolism with Lumen.

When my reading after a workout is a one (burning more than 84% fat) however, I know my workout was limited in part by the fact that I couldn’t get hold of the carbs, so I wasn’t able to exercise at the highest intensity. This was also reflected by the way I felt: I was destroyed.

Now I know to replenish my carbohydrate storage before a workout around the same intensity.

With CrossFit® being such a high intensity sport, starting a workout with a Lumen score of one is not a good idea. I have found that, more often than not, I feel great and ready to tackle a workout, yet my carb stores are depleted and I’m burning mostly fat. So, even when I feel good, it’s been incredibly useful to know that, in order to make the most of my upcoming workout, I should fuel myself properly for it.

Lumen metabolismSource: Lumen
Like having a nutritionist in your pocket.

With workouts I’m comfortable with – anything to do with long endurance – I thought I wouldn’t have to worry too much about my fuel. And I was right, what Lumen has done for me there, despite my not needing to make a change, is told me that I’m doing well in that area (my body is not limited by my energy delivery) and I should focus on other areas to improve.


Using Lumen before and after mealtimes has also been incredibly interesting. The ability to see what my body is doing before a meal and how (and when) it reacts to it is a game changer. After four carb servings, when does my body shift from using mostly fats to burning both fats and carbs? Do the carb servings have an effect at all? Does it take thirty minutes or an hour? What if it was only two carb servings?

With this knowledge, I now know what and when to eat to fuel efficiently and effectively for my workouts.

Everyone has a different metabolism. To know what source of energy you’re using at any given time is not only a really interesting bit of information and insight into our own bodies but is also incredibly useful.

For me, it has meant I can use science, rather than guesswork, to fuel myself specifically for performance, optimise my workouts and keep better track of my nutrition.

What I like about Lumen the most is how actionable it is. I breathe into it, it provides me with data and I can do something about it.

Everyone’s metabolism is constantly changing, and your source of energy will vary depending on the time of day, the activities you’ve done, the food you’ve eaten, your stress and sleep levels. To have the ability to know whether you’re burning fats or carbs whenever you want is revolutionary.

Try it yourself

Lumen is a striking product; from the design of the physical device to the app, you can tell a lot of thought and effort went into making these smooth, incredibly user friendly and high quality.

The materials used for the device look and feel superior, holding it is intuitive and the way it interacts with you feels right. All information presented on the app is clear and easy to understand, and while the topics might seem complicated, everything is broken down into understandable slides.

Lumen is a quality-built product, the design truly stands out, and the data it provides you with is incredibly valuable.

Buy it now

lumen metabolic device

Image Sources

  • Taboola cover pics Lumen: Lumen
  • Lumen-metabolism-breath: Lumen

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