Fat vs carbo consumption

Greetings to all.
I looked for a similar topic but did not find anything.

Yesterday I did an hour of ‘Zone 2’ aerobic training with 12 minutes of warmup before. HR interval 118 to 128bpm (anybody follows MAF HR calculation?) which is a typical fat burning endurance workout.
The activity report shows a fat consumption of 10gr vs 96gr of carbohydrates.
How are these macros calculated in XERT?

Thank you!!!

Hi Alessandro,

Good question. Xert estimates Fat/Carb utilization based on your actual power, relative to your fitness signature. Generally, you’ll see the largest fat burn around LTP, while carbs start becoming the more predominant fuel source the higher above LTP that you’re riding.

If your signature is dramatically underestimated in our system, then the estimation of carb/fat burn will likely be incorrect. Do you think your TP in the system is accurate?

You can read more about our Fat/Carb calculations in our documentation: http://baronbiosys.com/fat_and_carb_utlization/

Hi ManofSteele, nice nickname!!!
I have tested Xert Fat/Carb for 10 days in order to reply properly.
I am training following Dr. Maffertone 180 rule for HR for endurance. I am 47, not a professional athlete, but I measure and like to obtain improvements. My goal is to loose weight, boost fitness and train for a Triathlon Sprint in 2021.
The Maffertone method consists in improving training level maintaining a fixed hart rate interval and in the meantime trigger fat usage for energy. I have been following this training for almost 2 weeks now and even XATA realizes the fast improvements in TP and endurance. And observing the suggested trainings that XATA gives me, they are very similar to MAF HR trainings.
I have been following also a purifying no carb paleo keto diet (tons of vegetables and organic grass fed meat, poultry, fish, healthy vegetable fats, nuts, olives…) and I have never felt so full of energy during the day and during training. For now I limit sessions to 1 hour + warm up/cool down (total 1h 24m) just because of the discomfort of the saddle and being bored to sit on a trainer for so long.
I do feel I have triggered fat use for energy (also lost weight), but XATA still tells me I have burned three times more carbs than fat.
My training is between 118 and 128bpm HR, average 105/110W (just barely above LTP) and increasing distance covered over time. Once a week I then also do a HIIT training to make things challenging.
Sorry for the long and tedious reply… just wanted to make the picture clear.

Kudos for the scientific approach! It’s worth noting that Xert won’t/can’t take any consideration of your diet and fuel sources, but it’s great that you’ve found a balance that leaves you feeling so energetic.

What does your fitness signature look like? I was surprised to see your fat/carb ratio, as for me I am around a 1:1 ratio when riding at LTP. Being a bit higher (270W) I would expect that to be more carb-hungry than riding at 110W.

I’m wondering if your LTP/FTP are quite close, hence Xert assumes you are using a lot of carbohydrate?

Hi Adam, thank you for the kudos.
I like your description of a ‘scientific approach’ :joy::joy::joy: I’m just curious about certain human body dynamics. Kudos to you for your high TP!!!
You are correct, my LTP and TP are still very close at 99W and 131W respectively. I don’t have a power meter on my bike, only on my smart Tacx trainer, so to increase the gap I need to do longer endurance rides, but believe me 1:30 hours on a trainer seem forever to me… if I go out on the bike I can ride for 2 hours or more and don’t feel it. I guess I have no choice than to invest in some sort of a pedal power meter.
This is my last training profile, perhaps you are more scientific than I am…

There is quite a bit of sensitivity to how much fat vs. carbs you burn in between LTP and TP, so if LTP is a few watts too low, you’ll see Xert attribute more towards carbs than fat at a wattage in between. At 13.1kJ of HIE and 423W PP, your HIE might be a bit high and thus LTP may be a bit too low (see our FAQ on how to evaluate your signature) which would explain the discrepancy.

I realize it’s hard to evaluate this on your own. Normally the best approach is to push a longer effort (bring MPA close to TP) with a breakthrough which will help determine if HIE needs to be lowered and LTP raised.

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Hi Armando, thank you for your reply. You are correct, it is difficult to evaluate so many parameters for a new member, despite my curiosity and ‘scientific’ approach. Considering a generic assumption our bodies store about 1500-2000kcal of glycogen and 30.000-40.000kal of fat to depend on for energy, in your experience, how can I ease dependance on fat for energy with my actual fitness signature. From my side I’ll try to stay on the trainer for a longer session untill MPA comes down to TP as per your advice.
Thank you Boss for your advice.

To increase the relative utilization of fat vs carbs, you need to raise TP and/or lower HIE. In practical terms, this means longer, easier training
closer to LTP than what you do normally. It is interesting to see that the advice drawn from Xert’s numbers aligns with what most coaches advise in practice.

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Screenshot 2020-06-18 at 07.53.23
According to this chart your Peak Power could be underestimated or your HIE overestimated which would affect the calculation for your Fat/carb ratio.
Have a read of this: http://baronbiosys.com/faq-items/is-my-fitness-signature-right/?fbclid=IwAR2mV0mlMXne5k5pm8cFJ4p0tmgO1PxOsBYELqdezKQGH7RWJC9fuh5k2nE

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Interesting reading guys.

Gr Johan

Hi Armando, ok I will adapt my training sessions and let’s see what happens to numbers.
The Dr. Phil Maffertone MAF HR training approach is similar to XATA calculated trainings only for endourance ones that advice long sessions around LPT that develop your aerobic engine. Specially in the pre-base/base area. You can then also insert HIIT up to not more than a certain percentage (I do not recall the exact number, but roughly remember something like 20-25%).

My understanding has been that maximum MAF heart rate would correspond to a power about 10% lower than LTP as at LTP you’ve actually gone above base line lactate production and your carb consumption is already starting to ramp up. The MAF limit sets it lower so you are burning minimal carbs. However tis is a topic of seemingly endless debate on other forums.

Hi Cary.
Dr. Maffertone’s MAF training is based on heart rate, not power. Te idea is to build and increase your power and overall fitness level maintaining the MAF HR range. This is vital for endurance athletes and triathletes. The rough rule to calculate the MAF HR range is 180 minus your age: there are then some parameters to take into account to adjust properly this number. Details can be found at https://philmaffertone.com/180-formula/
I calculated my MAF HR range and it is 128-118bpm (I am not an athlete and haven’t been training consistently for 2 years and in June 2019 I had pneumonia infection). Personally to stay within this range on a static trainer on the bike I am using now I pedal at about 85-90rpm expressing 100-110W which is about equal or 10% higher than my LTP. I can fully understand the debate around this topic, specially because for a lot of people training at low HR feels awkward and useless. Others found it absolutely illuminating and soled their training problems.
Armando and his XATA is a wonderful invention, I could never revert to an other platform, and for no reason my MAF HR topic wants to interfere. I am just trying to integrate positively the two things in an intelligent way and improve my fitness level as a non athlete aiming to work up to become one next year.
Anyhow I read somewhere that the difference between being an amateur or an athlete is when you start examining and monitoring your performance. :slight_smile:

So, I did a ~3,5 hour, 115 km ride this morning and didn’t eat, only drink - Precision Hydration tabs in water - and I wonder where the carbs that Xert calculated came from?

I.e. as there is no way to tell Xert what I consumed, is the calculation solely based on power?

In rough numbers your body can store 500g of carbohydrate. Even though you didn’t eat any, you would still be consuming some carbohydrate to generate your power.


Interesting - so, in theory I could go for ~10 hours without eating and burn carbs from this store?

Considering that this accounts for ~ 2000 kcal, I’d get the remainder out of my fat store? That would be somewhere near 6000 kcal, or 750 grams of fat.

In that case, Xert’s math is not that bad :sunglasses:

(Although I doubt I’d succeed in completing the quest to prove it)

That came up on a recent Fast Talk podcast episode, actually. I’m simplifying, but essentially your body wouldn’t let you get down to anywhere near 0 and would apply the brakes. Your maths checks out though!

I sort of tested this doing a virtual Everesting ride a couple of months ago. 14 hours @ 183W average (my LTP was around 250W at the time and I was climbing at 210-230W) so lots of time at low intensity.

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