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The Fuel Mix - Fuelling for Endurance




Using something called your Respiratory Exchange Ratio (RER) can help with setting your zones, but also makes fuelling easier. Your RER highlights what fuel you are using - carbs vs fat?


At rest, your RER should be around 0.7 indicating you’re burning mostly fat and as exercise intensity increases gradually you move to 1.0 = 100% carbs.


OK but how does this relate to training zones?


Your Aerobic threshold is the point at which you switch from an easy intensity (usually top of zone 2) to a moderate intensity. The RER here is normally 0.85. This indicates a 50:50 split in carbohydrates to fat usage. So, zone 2 work and below, which is under 1 hr won’t rely on any carbohydrates (stores will suffice), anything above them you could fuel a little.


Your anaerobic threshold (zone 4 in a 5 zone model or top of 2 in a 3 zone model) is normally around 1.00. which as mentioned above, means it needs fuelling with carbs. So for sessions above your AT you need to make sure you have more carbohydrates as you will burn through them fast!


If it’s somewhere in between, it will be a mix. So this is where you have to practice! How’s fuelling, how’s body composition. Progress should help dictate changes over time.


If you’re interested in finding out your fuel mix get in touch and arrange some testing >> www.boxnutrition.co.uk/metabolic-testing


#metabolictesting #aerobicthreshold #fuellingendurance

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