Carbohydrate and fat combustion rates are among the most important features INSCYD can offer for runners, triathletes and cyclists.
Here’s why: While fat combustion rates are a valid marker to monitor training progress and set training intensity zones, carbohydrate combustion is crucial not only in training – but even more in a race.
Carbohydrate storage is very limited in the human body and so is the uptake rate an athlete can tolerate when training and racing. The upper ceiling of carbohydrate intake per hour is around 60 to 90 g/h; but that also depends on the type of carbohydrates the athlete take in and how these types are mixed. Now, compare this stats to the actual carbohydrate combustion rate your athlete could face at the anaerobic threshold: a 70-kg age group triathlete can easily combusts 250 g of carbohydrate per hour and a professional cyclist (75-kg) can easily double that amount to up to 500g per hour, or even more.
This said it becomes clear that managing the effort in a race that lasts several hours – like a gran fondo bike race, a marathon, a half Ironman or a full Ironman race – is key for a great performance. On the given day, and given the specific training status, the perfect pacing strategy depends on three elements:
How many grams of carbohydrates do your athletes actually combust?
How big are the glycogen storages of your athletes?
How many carbohydrates can your athletes take in an hour?
With INSCYD you hold all the tools you need to setup the perfect pacing and fueling strategies for your athletes.
1. Carbohydrate combustion rate
Three weeks before the targeted race, carry out a performance assessment with your athlete. A good time for this – chosen often by INSCYD coaches – is the end of the last training block, just before the beginning of the tapering period. In the INSCYD metabolic profile you will find the fat & carbohydrate combustion rate as a function of power (in cycling) or speed (in running). The red graph shows you the carbohydrate combustion rate in kilocalories per hour (kcal/h) but also in grams per hour (g/h). Use the cursor to move over the graph to read the precise carbohydrate combustion rate at any given power or running speed. You will need this later to calculate the best power / running speed for the race.
2. Glycogen storage
There are a lot of scientific studies that took into account the amount of glycogen stored in the human body muscle. Here are some guidelines:
Untrained individuals; approximately 15 g per 1 kg muscle mass
Trained individuals; approximately 20 g per 1 kg muscle mass
Professional endurance athletes; approximately 25 g per 1 kg muscle mass.
All those guidelines relate to a full recovery status, and that means at least 2 or 3 days with no (or very light) training and a high carbohydrate diet. For a non-professional athlete, 20 g of carbs per kg of muscle mass has been proven a very accurate estimate. Even professionals, though, and mainly because of the pre-loading training (one or two days before a race), hardly start a race with 25 g/kg muscle mass.
But how much muscle mass are your athletes actually using during the effort? Nothing simpler than this: open the “advanced body composition” menu when you run an analysis with INSCYD. Here you will find an estimate of the amount of used muscle during the effort. To calculate it specifically for your athlete and help you to better understand the concept, we build an excel tool for you to run this calculation (see attached to this post)
3. Carbohydrate intake during the race
The most common and general guideline for carbohydrate intake during a race is to stay at around 60 to 90 g per hour. For long time, 60 g was seen as the maximum possible rate, but recently studies have found out that different kind of carbohydrates (for example fructose and glucose) use different transport mechanisms. The 60 g/h was the ceiling of one specific transporter, but if the body uses different carbohydrate transporters and from a mix of different kind of carbohydrates, the upper limit rises up to 90 g/h. To be clear here: these rates do not mean the amount of carbohydrates your athlete can swallow in one hour. The bottleneck is the uptake from the gastrointestinal tract into the blood. So even when practicing to take in more than 90 g/h, not much more than this will actually get into the bloodstream and therefore available to the muscles.
In any case, you should have your athletes practice the carbohydrate intake in training. To take in around 60 g/h should be easy to achieve, while only few athletes can ingest 90 g/h. Plus, it also depends on the type of exercise: ingesting 70-80 g/h on the bike is doable for several athletes, whilst during the run even 60 g/h might be tough.
Putting it all together -5 Steps to calculate marathon pacing:
Now, in order to calculate the best pace for a race, you now need to combine all the three different aspects.
Step 1. Start with the estimated duration of the competition.
Step 2. Multiply the event duration (in hours) with the carbohydrate uptake rate (per hour).
For example: the goal is to run a marathon in 3h. We assume a carbohydrate intake rate of 50 g/h (so a relatively low intake rate). The total carbohydrate uptake rate is 3 (h) x 50 (g/h) = 150 (g) of total carbohydrate intake.
Step 3. Estimate the glycogen storage. Let assume our athlete weights 75 kg, he’s a male and has approximately 12% of body fat. His total muscle mass is 40%, which equals to 30 kg (75kg x 40%). During the run, we assume he uses 70% of his total body muscle mass and therefore we get a total of 21 kg of muscle mass used. With a glycogen concentration of 20 g per 1 kg muscle mass we get: 20g x 21kg = 420 g of total glycogen available in the muscle involved during the marathon.
Step 4. Add the 150 g of carbohydrates which is the total intake as calculated in the previous step. This gives us a total carbohydrate availability of 420 g + 150 g = 570 g.
Step 5. Divide this by the duration of the race – that is 3 hours in our case. This leaves us with a carbohydrate combustion rate of 570 g / 3h = 190 g/h.