sryke wrote:
DrAlexHarrison wrote:
sryke wrote:
On the 120g intake, one thing I've already wondered when coming across this mountain marathon runners study some time ago is the hydration. Ambient temperature was 10°C in the study, methods section says only "hydration ad libitum". I don't believe folks went with perfect isotonic concentrations under these circumstances. Any word from Gusatv Iden on this? How do they manage fluid intake at these higher rates? They simply train to tolerate hypertonic conditions in the gut? I mean we all know the reasoning behind isotonic solutions. These higher rates contradict these.
My responses in this thread might shed some light on your questions about hydration and high rates of carb consumption: https://forum.slowtwitch.com/...t=last-7417228#first Yes it's a balance between maximizing carb absorption and maximizing hydration. Maximizing hydration and carb consumption probably cannot be done simultaneously. Optimization is the goal. Hypertonic solutions are a good idea. Isotonic solutions are rarely a good idea for maximizing performance. The notion of isotonic solutions came about because of one-stage thinking and lingers today because of dogma, and assumption that fueling for ultra-distance events should inform fueling practices for events lasting less than 10 hrs. Uppermost limits for even the most well-trained folks appear to be 150g/hr and 1-1.2 L per hour... but maybe not at the same time. But also maybe yes. Size of human matters much less than training to do it and executing it well. Perhaps you can put this study into context, why did the 120g do worse than the 90g? Should they have used 1:1 instead of 2:1? https://www.ncbi.nlm.nih.gov/...articles/PMC5789655/ Yes, precisely. Exceeding 60g/hr of glucose alone starts to come with potential tradeoffs. Exceeding 70g glucose per hour is guaranteed to be suboptimal for at least some of the subjects. Only the most high-carb-trained guts are going to tolerate 75g of glucose hourly, and of course, only in pretty optimal conditions.
Further, I'd expect that highest intake rates (100-150g/hr, broadly speaking) would be most beneficial for events lasting longer than 2 hrs but probably shorter than 6-10 hrs... very little research (if any?) done out at those durations, related to high-carb intake and the hydration balance issue.
I would love to see researchers study a 3-4-hr effort in cool/mild conditions with good airflow, with the following test groups:
90g/hr @ 2:1 gluc:fruc (as the "control")
90g/hr @ 1.5:1 gluc:fruc
90g/hr @ 1:1 gluc:fruc
110g/hr @ 1.5:1 gluc:fruc
110g/hr @ 1:1 gluc:fruc
130g/hr @ 1:1 gluc:fruc
150g/hr @ 1:1 gluc:fruc
130g/hr @ 0.8:1 gluc:fruc
150g/hr @ 0.8:1 gluc:fruc
To future researchers who read this: consider using sucrose for the 1:1 options because of lower osmolarity than maltodextrin:fructose.
But that's a LOT of testing conditions... so probably a decade of research or more until we'll know better.
For that to ever happen though, researchers are going to need to stop saying "therefore it appears that 110g/hr is additionally beneficial compared to 90g/hr for endurance exercise." It's simply not true. It's only true when you constrain it to less than 2.5 hrs of exercise, and when the ratio is constrained to 2:1. Under those constraints, yes, 110g/hr is no better than 90g/hr.
Unfortunately the time constraints are logistical and understandable in a research setting.
The ratio issue is a matter of dogma needing to perish. You can't go 2 clicks on the internet without seeing the numbers 30, 60, and 90 thrown around. When nice round numbers are oft-cited, be on the lookout for dogma. Example, article I wrote: https://www.trainingpeaks.com/blog/how-to-optimize-carbohydrate-absorption/ TLDR: consume 90-140g/hr, not 60 or 90. Meanwhile, a link WITHIN the text of my article links out to another article that says quite the opposite, and worse yet, it's written by a guy who should WANT you to consume more carbs... given that his company sells them for a living. https://www.trainingpeaks.com/blog/carbohydrate-king-endurance-performance/ Quote from article: "We can only absorb around 60-90g of carbohydrate per hour during exercise" LOL. I don't blame him. But, you know the dogma is thick and blinding to researchers in the industry, when the very people who are incentivized financially to tell you to consume more of their product, are still blindly citing the same nice round numbers. ;)
Dr. Alex Harrison | Founder & CEO | Sport Physiology & Performance PhD
-------------------------------------------------------------------------------------------------------------------------------------------------
📱 Check out our app →
Saturday: Pro Fuel & Hydration, a performance nutrition coach in your pocket.
Join us on YouTube →
Saturday Morning | Ride & Run Faster and our growing
Saturday User Hub