Should I care about fat utilisation?



Eldrack

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Jan 10, 2005
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One of the adaptations to endurance exercise (specifically sub maximal L2/L3 stuff as opposed to L4 or higher where you burn mostly carbs) is the increased ability to oxidise fat as opposed to carbohydrates. Lots of studies have been done into this and demonstrate that endurance training increases "time to exhaustion" at various sub maximal exercise intensities.

Most of these studies don't take into account refueling however. Clearly if I have no food accessible to me then being able to burn more fat is great, I'll last longer at a given submaximal intensity. But if I'm cycling along in a road race or a triathlon or just on a long training ride the option to shovel carbs into my face throughout the entire ride is there for me (up to a certain limit of course - my gut can only take so much).

I've read some stuff (see below) recently about maximising the fat utilisation adaptation by training at moderate (high L2/low L3) intensity whilst low on carbs (either by training in the morning or depleting carbs during a long session etc or even just using a low carb diet). The idea is to maximise PPAR-Delta levels (which are higher when glycogen is low) whilst burning fat for fuel.

My question is: Should I care about increasing my fat utilisation? Given that in any race I'm going to be able to eat enough carbs to prevent me from ever being carb depleted are there other benefits to having upped my ability to burn fat for fuel? This adaptation will happen anyway as I do my L2/L3 work (which I'll still do for other endurance adaptations such as increased capillarisation etc).

Taking a more extreme view you could say focusing on increasing fat utilisation could harm other adaptations - you won't be able to maintain as high an intensity for as long as you're in a glycogen depleted state. You also won't be practicing fuelling on the go (training your gut being quite important as well).

Does anyone here think it's worth focusing on increasing fat utilisation (maybe to help stay thin)? Or is it a relatively irrelevant (given our access to carbs) byproduct of endurance training that isn't worth focusing on (or at worst detrimental!).



Background articles:
http://www.pponline.co.uk/encyc/strength-and-endurance-training-how-athletes-can-maximise-their-performance-42126 (the info in here around AMPk could provide an arguement for not using carbs during a training session as it decreases AMPk activation and therefore generation of new mitochondria... however I don't think there's a reason not to start the training session loaded up on carbs - all you're looking to do is maximise the disruption to the cells energy levels and being preloaded with carbs helps you train harder?)
http://www.pponline.co.uk/encyc/sports-nutrition-the-latest-research-into-low-glycogen-training-42067 (the system they use in this seems a tad dumb in that they did high intensity exercise whilst glycogen depleted - based on the first article this wouldn't be the best way to increase fat utilisation, instead the second exercise should have been done in the "fat burning zone" instead)

Edit: PPAR-Delta not PPAR-Gamma!
 
As you said you can refuel with sugars. Given that, is is difficult to run out of glycogen training or racing to the extent most people do.

You want to match your training to your racing needs. If your current training is doing that, there is no reason to change.

Fat/glucogen utilization is a very complex issue. Any claims about the the relationship between effort and percent of calories supplied by fat are about as accurate as any formula is in computing maximum heart rate.

If you want to train at a certain percantage, you will need to do substantial testing first.

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Yesterday, I did an hour at mid L3 (power) on my trainer. I was in L3 (heart rate) for 20 seconds. It was a worthless training ride. (but it gets me off the couch on miserable days.)

L2/L3 (power) rides have utility for 2 groups of people. 1) Those who are new to bicycling. 2) Those who spend much longer hours on a bike than you do.
 
The best way to train increased fat utilisation at any given sub-maximal power is to improve your threshold power.

That's the long answer.

The short answer is no.
 
Speaking in generalized terms, the body stores around 400 calories of sugar and your body will massively prefer these whether exercising or not when available. If you can keep down more calories than you are expending (aka if you spend 800 calories on a shorter race but can take in an extra 400 calories that are easy to digest during the race [if they aren't there will be too much blood shunted from digestion to action to deal with the calories and you will be sabotaging yourself], then you're fine). Fat utilization is a matter of longer endurance races. The 3 carbohydrate energy systems can last up to ~400 calories used, for the average adult, and depending on what they train for. Along with the energy systems you use, while we have a certain propensity for certain ratios of muscle tissue types, if you train for beta oxidation, at those intensities and duration's, you will move more towards slow twitch fibers, aka endurance on top of endurance. If you are looking to train for races that are a lower duration or intensity, or you know you can keep enough sugar in the right form available...then the long endurance beta oxidation training will be counter productive. The more you train beta oxidation energy systems, and thereby slow twitch fibers (but note these are two different things, your fast twitch fibers will adapt to be better at beta oxidation AND you will develop the overall ability of your slow twitch fibers as well), the less developed your carbohydrate energy systems and fast twitch fibers will be.



So what is your energy source and what races are you doing?


I wrote an article you can find here about the energy systems themselves, and I think I included some info on the muscle fiber types as well. It's semi-technical. http://abcbodybuilding.com/forums/showthread.php?t=95907
 

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