Max Heart Rate

(ianrobo) #22

We should remember that we are all different and the best advice is to do what feels best and comfortable ?


Sorry for new reply on an old thread … how did this end up for you?
I recently switched to a very low carb diet for gut health reasons. I do a lot of biking also and my power is way off. Did yours get back to normal? Did your idea of carbing up right before your ride help? Did it mess up your diet?
Thanks for any info


Sorry for the late post on an old thread, but how did this work out for you? I bike a lot and since I started keto diet (gut health reasons, not to lose weight) my power is way down. I don’t know if I can safely work out in anaerobic levels without my body going after muscle, since glycogen is so low.


Eventually got my power back. I started doing some carbs morning of a big ride. I think it helps. Your going to burn it all of so it doesn’t make a difference. Also remember that loss of weight also means loss of some power.


Just did some controlled workouts on a trainer. @ 150 W, I used to be at 115 HR, now 130. @ 200 W, used to be 135 HR, maybe 150 now. However, the 130 HR effort “feels like” a 115 HR effort used to, if you catch my meaning - feels like Z1. My theory is that the ketones supply energy in a lower density per unit blood to the muscles compared with glucose, so the heart has to pump more.

At max effort over 15-20 seconds, I have about 950 W which is down 100 W from a year ago but I don’t attribute this completely to the keto diet.

Still haven’t really tried a max interval (1 minute, 5 minute, or 20 min) effort on keto. I’m scared of those - what will my body do when it really, really wants glycogen? I don’t want it going after muscle fiber.

Keep in mind I switched from a very high carb diet to a near zero carb diet about 8 days ago. Thx for any comments!!

(Bob M) #27

Riddle, you’ll have to wait at least a month if not several to get back to where you were, with the keto diet. Your body takes a while to transition to being able to use ketones efficiently.


Thanks! I guess my question is whether anyone doing the kind of exercise that normally requires glycogen EVER gets all their power back. I’ve not found anyone who did - think of HIIT exercise; high effort for 1-20 minutes.
Running/biking at steady effort for hours on end is at a low intensity and is properly fat-burning anyway. Weight lifting (5 reps or so) or sprinting is all ATP, cells have what they need; this also could be unaffected. I am not sure that the body COULD get the same energy over a 5 minute effort from ketones that it can get from glycogen. I’m fishing for someone (especially a bike nerd like me) who has data on that type of exercise but I think I will have to add back in carbs for heavy training days and race day.


@brownfat, the two articles from Peter are outstanding! Thanks for passing them on.


This is the closest thing I’ve been able to track down as far as a reasonable discussion on the subject.

Noakes is a keto evangelical, so I take everything he says with a grain of salt. I think the podcast itself balances that out to some degree.

The one study that I found somewhat close to settling the issue:

… but Noakes disputes the findings, since they were going through fat adaption during the study itself, as opposed to being fat-adapted before!

So I don’t have an answer, other than to say you’re not alone in having the question. :slight_smile: I don’t think it’s a settled matter.

Oh one other thing - there’s an Utramarathon guy Zack Bitter, he is a Keto athlete, but he does use carbs for certain training:

Granted, he’s doing 20h of training a week… so the carbs are gone pretty quick :smiley: … which I think is key. If you hit the carbs at the right time, they won’t spike insulin because your body is burning them as quickly as you’re getting them down your throat!


(Life is bacon, bacon is life) #31

Have you looked at any of the papers published by Phinney and Volek?


Not yet - thanks for the reminder. Within the week I think!




@Riddle you’ve got me going down a crazy rabbit hole.

I was reading this:

I don’t think there’s anything that should be that shocking here. As you get closer to VO2 MAX (ie. as intensity increases) your body shifts to use a higher amount of carbs for fuel.

I found this interesting though:

Maximal fat oxidation has been reported to occur between 47 and 75% of VO2max, and varies between trained and untrained men and women [1, 5, 6]. Nonetheless, MFO has been observed to range from 0.17–1.27 g/min [7], where ketogenic adapted individuals can exceed ≥1.5 g/min

Put another way - keto adapted folks can significantly increase the point at which the body starts really blowing through carbs, so can theoretically do more intense exercise than a carb-athelete before they “need” carbs.

They have a chart that shows the crossover-concept…


… so basically a fat-adapted athlete should be able to move that point over, so that intensity can increase before CHO (carbs) become dominant fuel.

Diets that have higher proportions of a specific macronutrient (e.g. fat/CHO) have shown an increased ability to oxidize the primary macronutrient consumed [66–68]. Furthermore, endogenous substrate concentrations increase after acclimating to high fat/high CHO diets [65, 68, 69]. High fat diets increase IMTG concentrations while decreasing glycogen levels within muscle [17, 35]. Alternatively, high CHO diet conditions increase glycogen concentrations while IMTGs decrease [17]. After acclimation, during exercise the body favors oxidation of specific substrates [65, 67] based on long-term (>48 h) cellular adaptation in accordance to macronutrient consumption [3, 35, 69]. However, post-exercise predominant macronutrient (CHO) consumption has been shown to influence cellular protein expression in as little as 2 hrs [69]. The plasticity of cellular changes relevant to chronic adaptation are compromised when macronutrient content is altered.

Basically: if you eat fat as primary, your muscles adapt to store fat as primary. If you eat carbs as primary, your muscles adapt to store carbs as primary. And they adapt quicker than you think.

IMTG = fat stored in your muscle fiber (not your belly).

And here’s the big one:

However, during sustained high intensity exercise (>70% VO2max) which is common during competition, CHO is the primary substrate relied upon despite short and long term fat acclimation

CHO is carbs. So if you’re going high intensity… the carbs matter.

There’s also something there about adapting to fat, then doing a carbo-load like Zack Bitter does (see the link I posted earlier).

And it’s all highly personal, so your VO2 max crossover and mine could be wildly different.

All of which is to say… it’s complicated.




@Jono , Many thanks! Yep, no surprises but great insights. Probably if I am better fat adapted it could really help for day-long rides, where you won’t have enough glycogen in any case. For the last 2 years I have been focusing on 1-2 hour high intensity stuff, SUPER glycogen-dependent. So this is probably good for me but at the moment I suck at it!!! (pedaling that is; the diet itself is going fine!)
Thanks again