DETERMINE YOUR CARBOHYDRATE COMBUSTION RATE AND FUEL YOUR PERFORMANCE

I recently spent some time with an athlete who is looking to get back into training after some down time in the off season. Coming off the back of a lay off is always an interesting time for athletes, particularly on the bike.


Have you ever come back from a bit of a break and wanted to get straight back at it with the power you were able to produce at your peak in the summer? I am sure it is something that we all have tried previously. Without doing any testing maybe you would knock 20-30 watts off their FTP and then get back into it. But is it the right approach?


For the majority of cyclists and triathletes out there we use Functional Threshold Power as a benchmark for our testing, setting training zones and race planning. But there is more going metabolically than a standard threshold test will show. It’s really important to take a deeper dive into what is driving this FTP number. We have touched on this in a previous article on

How FTP is Composed, but for now I want to show that knowing your carbohydrate burn rate is particularly important coming back into training.


Carbohydrate burn rate is simply the rate at which we individually use carbohydrates as energy during exercise. The two main energy sources during exercise come from fat and carbohydrate combustion. The easier the intensity of exercise the more fat you use and the higher the level of intensity the more carbohydrate you use. But in reality bellow threshold you are using a combination of both fats and carbohydrate to fuel your training/performance.


If you have a high Vlamax and are more explosive and anaerobic by nature you will have a higher carbohydrate burn rate. During what most now call the base period a lot of emphasis is placed on training the aerobic system to increase fat oxidisation rates and improving the aerobic energy. But, what if even though you think you are training easy you are actually not training easy enough. Let’s use an example of an athlete who recently came in for a test.


The graph below shows the fat and carbohydrate combustion rates for this athlete. The athletes FTP number is now 270 watts. If we apply the standard approach to setting race pacing to be 70-75% of this number it leaves a range of 190-202 watts. If racing tomorrow at a target of 200 watts then required carbohydrate to sustain this effort is 75.6 g/h. This level of carbohydrate replenishment is a comfortable rate to consume.

During the summer he posted a very impressive 20 min time trial best of 336 watts. Using the most common approach to FTP testing and taking 95% of this number that leaves this Ironman athlete with an FTP of 320 watts. Since he primarily races Ironman distance races another assumption is made that he should be able to sustain 70-75% of this number, or 224-240 watts.


But now these numbers are not relevant. 220 watts may feel particularly easy for this cyclist. But at 220 watts a sustained effort now requires over 100 g/h of carbohydrate. For a lot of athletes this rate of consumption might lead to GI issues and a deficit of energy going into the marathon at the end of the race. Without knowing what is happening metabolically the athlete may also fall into the trap of easy K’s not being easy enough. This could really have implications for building the aerobic base.


FTP is but a number and it may now be time to start redefining how you approach training. Seeing carbohydrate burn rates may open a window into why athletes sometimes fail to hold 70% of the FTP on race day without cooking their legs for the run.

Thanks for reading

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