Carbs per hour for endurance rides different than tempo and above?

A light bike doesn't replace good fitness.

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Shrike
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by Shrike

I'm thinking about doing some long rides again, bit behind schedule to a lot of stuff, but I've got a free day tomorrow and want to test a new saddle bag and fuelling strategy for really long stuff. Will start with something around 130miles and hopefully try the magic 200 a few weeks later.

I used to eat 60 grams of carbs per hour when doing 100 milers. Likely over that, but I was definitely maxed out.

When fuelling for really hard efforts, like 2 hour full gas efforts, I'd also be maxing out the carbs per hour.

Surely the endurance stuff doesn't require as much? Shouldn't we be fine with say 20 to 30g of carbs per hour and the rest from body fat?

Also, usually I use maltodextrin in bottles to strictly control carbs per hour, but bought some dextrose to try this week. No downsides to it? Never used it before and I'm thinking it shouldn't be an issue. Seems sweeter though?

by Weenie


TobinHatesYou
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by TobinHatesYou

You can game your glycogen metabolism by ingesting multiple types of sugars. That's why some gels have combinations of maltodextrin, dextrose and sucrose. That's really only a few percentage points though. On 3-4hr hard rides, I usually take in around 80g of carbs/hr in gel/goop/liquid form because I don't get much GI distress from that. Better to err on the side of overdoing it than bonking earlier.

Personally I don't get along well with solid food on the bike. They tell my brain I want to poop...it's completely neurological. Also I just hate having a big dry energy bar soaking all the moisture out of my mouth as I fail to get it down.

joejack951
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Location: Wilmington, DE

by joejack951

Interesting question. I Googled some stuff and found a study which suggests that in the 'fat burning zone' you can expect to utilize fat for 1/3-1/2+ of your calories expended per minute, as opposed to when in the aerobic zone where it's more like 1/8-1/3.

From the study:
Image

Link: https://journals.lww.com/nsca-jscr/full ... ne.25.aspx
Last edited by joejack951 on Sun Aug 04, 2019 5:32 pm, edited 1 time in total.

JoO
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by JoO

When you are riding slower your ratio of used fat/carbs goes up. (how much can only be determined in the lab using a breath analyzer)
It also becomes easier to digest carbs.
I am absolutely fine with 20 grms/hour but I have trained my body to be efficient in fat burning (e.g. running 1.5 hour fasted)
If your training is more interval/high intensity based (1-2 hour sessions, SWIFTing,..) you might need more.

TobinHatesYou
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by TobinHatesYou

JoO wrote:
Sat Aug 03, 2019 1:28 pm

I am absolutely fine with 20 grms/hour but I have trained my body to be efficient in fat burning (e.g. running 1.5 hour fasted)
If your training is more interval/high intensity based (1-2 hour sessions, SWIFTing,..) you might need more.

Pretty much anyone should be able to ride Z3/Z4 for 2 hours "fasted" without bonking.

jasjas
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by jasjas

That is upper tempo/threshold for 2hours, fasted means not having eaten for at least 12 to 14 hours, so for me (& it is personal) i'd want a carb drink and some food after an hour, i wouldn't bonk but i'd start going slower!

As for endurance riding, just done a 4 hour ride (800m of ascent) on a banana, a 20gram fruit bar & water.

Home made rice cakes with fruit are quite moist!

Shrike
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Joined: Fri Jun 03, 2016 5:08 pm

by Shrike

joejack951 wrote:
Sat Aug 03, 2019 1:37 am
Interesting question. I Googled some stuff and found a study which suggests that in the 'fat burning zone' you can expect to utilize fat for 1/3-1/2+ of your calories expended per minute, as opposed to when in the aerobic zone where it's more like 1/8-1/3.

From the study:

Image

Link: https://journals.lww.com/nsca-jscr/full ... ne.25.aspx
You think that means we can drop carbs per hour by the same ratios?

I'm thinking maybe yes, but.. unsure.

Maybe it works more like you can simply maintain the say, 60g of carbs per hour, and forego the extra calories from other food sources, when doing a long endurance ride. Which is basically what I did today (though I used 50g per hour from dextrose only, no other food).

Near the end of the ride (around 7hr 30min) I did some intervals to test what sort of available energy I had left - I did a 25min tempo effort. No problem. Then I did a 7 minute threshold effort. Again no problem. So clearly there was more energy in the tank that I was needing, by only taking in 50g carbs per hour (200cals).

Worth noting that my power was lower end endurance zone, lots of coasting on downhills. Average watts at end was in the area between recovery and endurance. Over 5000kj effort.

Definitely feel there's some fundamental principle I'm not getting. Want to try again, but with slightly lower carbs per hour, or same again but for longer, like 200 miles. Would be amazing if you could simply roll along on like 40g carbs an hour and ride for 10 to 12 hours like that!

joejack951
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by joejack951

Shrike wrote:
Sat Aug 03, 2019 8:30 pm
Definitely feel there's some fundamental principle I'm not getting. Want to try again, but with slightly lower carbs per hour, or same again but for longer, like 200 miles. Would be amazing if you could simply roll along on like 40g carbs an hour and ride for 10 to 12 hours like that!
I think you are getting it but part of you is denying the science. Your last comment is spot on: at a certain exertion rate you could essentially ride all day simply topping up carbs a bit while using mostly fat for energy. Consider that 500g (0.5 kg) of fat has 4500 calories available in it (9 calories per fat gram). Most of us have well over half a kilo of fat on us to burn which in itself is enough to go on for hours.

Shrike
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Joined: Fri Jun 03, 2016 5:08 pm

by Shrike

joejack951 wrote:
Sun Aug 04, 2019 1:29 pm
Shrike wrote:
Sat Aug 03, 2019 8:30 pm
Definitely feel there's some fundamental principle I'm not getting. Want to try again, but with slightly lower carbs per hour, or same again but for longer, like 200 miles. Would be amazing if you could simply roll along on like 40g carbs an hour and ride for 10 to 12 hours like that!
I think you are getting it but part of you is denying the science. Your last comment is spot on: at a certain exertion rate you could essentially ride all day simply topping up carbs a bit while using mostly fat for energy. Consider that 500g (0.5 kg) of fat has 4500 calories available in it (9 calories per fat gram). Most of us have well over half a kilo of fat on us to burn which in itself is enough to go on for hours.
Thanks, but the part I'm sort of hung up on now is the huge calorie deficit that would be run up if you extended the principle.

Take a 14 hour easy paced ride at say around 150 watts roughly 550KJ per hour (550cals per hour for argument's sake), with fueling being 60g carbs per hour (240 calories)


Out: 7700 cal
In: 3360 cal

To fill out the picture you've got your BMR and whatever else you burn calories on that day, lets say 2000cals. Pre ride calories in, like breakfast (for me it'd be around 600 usually).

Total Out: 9700 cal
Total In: 3960 cal

That's a massive 5740 cal deficit!

Going by your fat/calorie numbers, you'd have burned over half a kilo of pure body fat, and should still not have bonked.

Can you really get away with that, or would some other factor kick in?

joejack951
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Location: Wilmington, DE

by joejack951

Shrike wrote:
Sun Aug 04, 2019 3:15 pm
Thanks, but the part I'm sort of hung up on now is the huge calorie deficit that would be run up if you extended the principle.

Take a 14 hour easy paced ride at say around 150 watts roughly 550KJ per hour (550cals per hour for argument's sake), with fueling being 60g carbs per hour (240 calories)


Out: 7700 cal
In: 3360 cal

To fill out the picture you've got your BMR and whatever else you burn calories on that day, lets say 2000cals. Pre ride calories in, like breakfast (for me it'd be around 600 usually).

Total Out: 9700 cal
Total In: 3960 cal

That's a massive 5740 cal deficit!

Going by your fat/calorie numbers, you'd have burned over half a kilo of pure body fat, and should still not have bonked.

Can you really get away with that, or would some other factor kick in?
I don't believe that when looking at calories expended during exercise that you would add in BMR on top of that. For short 1-2 hour efforts, the difference isn't huge either way but for a 12-14 hour effort, that ~1000 calorie standard burn during that period really adds up. But I believe it is encompassed in the typical calculations for exercise calories burned. So your total out number is more like 8500 for your theoretical 14 hour ride.

Further, the body stores about 2000 calories of easily accessed energy in the muscles when fully topped up. That's the reason I can go run/ride for a few hours (about 2.5-3 in my experience) first thing in the morning on just water and not bonk. So assuming you are able to use a large portion of that energy during the ride, the total deficit is now down to ~2500 calories, or about 0.25kg of fat.

Starts to sound more reasonable. Perhaps some Ironman or ultracycling/running participants can chime in with their experience. I've done one 12 hour ride but it was many years ago and I certainly did not fuel optimally for it. I'm still surprised I even managed to finish that ride given all the mistakes I made!

Shrike
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Joined: Fri Jun 03, 2016 5:08 pm

by Shrike

Yes! That sounds much better. So basically if you're doing a normal daily calculation for a small workout like 600 cals in 45 mins, it'd be something like 2000 cal BMR + 600 workout.

But because this is a whole day ride, you wouldn't do it as it's factored in. And even with the 45min workout day, you would still technically take 45mins off from the BMR figure if you wanted to be accurate?

TobinHatesYou
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by TobinHatesYou

2000kcal BMR is like a 200lb/90kg extremely fit 23 year old male, BTW.

Shrike
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Joined: Fri Jun 03, 2016 5:08 pm

by Shrike

I wanted to double check about the KJ value from power meter definitely including BMR, so I posted the question on TrainerRoad forums. Guys there are saying that the KJ value is isolated and only accounts for the work done on the bike, so you’d have to add BMR to your ride total.

TheRich
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by TheRich

Seems like an unnecessary risk to depend on fat burning to fuel anything past BMR.

Shrike
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Joined: Fri Jun 03, 2016 5:08 pm

by Shrike

TheRich wrote:
Mon Aug 05, 2019 8:08 am
Seems like an unnecessary risk to depend on fat burning to fuel anything past BMR.
The science points towards that's what's happening at a low pace. Small amount of carbs and a high proportion of fat. If you're just pootling along, seems unnecessary to be eating a lot of any type of food, carbs, fat or anything it seems.

This does seem closer to being on the right track again from what people are saying elsewhere:

Total Out: 9700 cal
Total In: 3960 cal

You really would be getting close to that huge 5740 cal deficit. Maybe knock a few hundred off as the BMR figure of 2k earlier also included other calories for daily activities, which you would get much of on a 12 to 14 hour all day ride.

So back to square one. Are you really losing half a kilo of body fat a day if you do a ride like that? If you're fully glycogen loaded you may dip into some of those stores, but shouldn't deplete them if in theory you're taking in 60g carbs per hour, which is likely more carbs than what's needed for an easy pace as it is..

by Weenie


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