Thursday, August 09, 2007

Is Muscle Fatigue Inevitable When You Exercise While On A Low-Carb Diet?

Anthony Colpo flashes rock hard abs he got while on a low-carb diet

A man I have grown to respect and admire over the past year or so is Australian independent researcher and certified personal fitness trainer Anthony Colpo. He's one of those polarizing figures in the world of diet and health that you either absolutely love or completely eschew! And he wouldn't have it any other way!

When I interviewed him at my blog in June 2006, we got a giant gulp of Colpo mania in one swell foop! The man just has a way of putting things in very plain language to confound his critics while educating the common man with plain, unadulterated truth.

Colpo's much-awaited debut book last year The Great Cholesterol Con helped fill the void left by the sudden absence of his wildly popular He then began a new low-carb bodybuilding forum site called in August 2006 to share some of the secrets he has learned about strength, fitness, and fat-burning.

These principles he has been teaching in one-on-one sessions with people have been in such increasing demand that Colpo decided to share them in his newly-released e-book called The Fat Loss Bible. It's a comprehensive plan to help cut through the typical dietary advice by educating you with scientific truths. I will be reviewing this book soon here at my blog and Anthony has agreed to another interview.

In the meantime, I occasionally receive a fitness-related question from a reader that is well beyond my own personal experience and/or knowledge. Such is the case with the following e-mail concerning muscle fatigue while livin' la vida low-carb.

Here's what he wrote in the e-mail:

Hey Jimmy. I've lost 20 pounds on Atkins and only have 10 more to go! I feel pretty darn good overall. Anyways, in regards to my exercise routine I go to a spin class at my local gym.

For some reason, though, I have muscle fatigue especially in my legs. I started taking a fiber supplement three days ago. When I went on the national spinning web site and looked up nutrition, they said if you spin on low-carb diets you're going to get fatigued.

Personally, I think that's just BS! Maybe you can discuss on your blog the benefits of low-carb eating on an exercise program. Maybe I just need to continue the fiber supplement and see if the fatigue improves.

Please continue your awesome blog. I visit it at least TWICE A DAY. It's so exciting! God bless you.

While I have experienced some muscle fatigue at times while undergoing mostly low-intensity exercising on my low-carb lifestyle, the severity has not been as crippling to me as it has this reader. It really depends on how long and vigorous the individual's physical workout routine is.

Because of that, who better to ask this low-carb fitness-related question to than Mr. Low-Carb Muscle himself, Anthony Colpo? He was more than happy to respond.

Here's what Anthony had to say about low-carb muscle fatigue:


Your problem is a common one among low-carbers, and here's why: low-carb diets, as prescribed by most popular authors, are hopeless for meeting the metabolic demands of any meaningful volume of glycogen-depleting exercise.

You are probably asking, "What the heck is glycogen-depleting exercise?"

Low intensity activities, like walking, jogging, or light cycling rely heavily on fats for energy production. After adapting to a very low-carb diet, performance during these activities is not usually adversely affected.

Higher intensity activities (those performed at 75% VO2 max or greater) rely primarily on glucose to meet the energy needs of working muscles. Most of this glucose comes from the working muscles themselves, where it is stored as glycogen. These activities are known as 'glycolytic' and include such forms of exercise as body building, fast running or sprinting, mixed martial arts--and spin cycling.

Sometimes low-carbers can perform a low volume of glycolytic activity and not notice any untoward effects. That's because they're not depleting the glycogen stores of the working muscles to any great degree. If the only glycolytic exercise you do is a relatively brief weight training workout 2-3 times a week, you may feel just fine on a strict low-carb diet.

However, the picture changes dramatically after you introduce activities that make deeper inroads into your glycogen stores. These activities will deplete glycogen from your working muscles faster than your diet can replace it. The inevitable result is fatigue, premature exhaustion, and reduced performance. One of the telltale signs of glycogen depletion is a 'heavy' or fatigued feeling in the working limbs - which is exactly what you are experiencing.

I'll tell you what to do about this in a second, but first I need to warn you about something. Many low-carb devotees of the armchair variety insist that low-carb diets can indeed fuel glycolytic exercise, and that the symptoms you are experiencing are occurring only because you are not yet "fat adapted." According to these folks, you just need "to give it more time".

Let's set a few things straight:

First of all, fat-adaptation almost always takes place within the first 10 days of switching to a low-carb diet. This is the cause of the notorious but short-lived energy 'crash' that many folks experience shortly after switching to very low-carb diets. In a study with competitive cyclists, Phinney et al found that 4 weeks of a ketogenic diet did not affect cycling performance at low intensities. The cyclists complained of the characteristic energy crash during the first 7-10 days, but after that their performance at 60-65% VO2max returned to normal. However, their ability to perform more intense activity (sprinting) deteriorated[1].

This was not due to a lack of "fat adaptation." Respiratory quotient (RQ) testing confirmed that subjects had indeed become fat adapted. Measuring RQ is one of the ways in which researchers check how a person's fat adaptation is progressing. This is typically expressed on a scale ranging from 1.0 (pure carbohydrate oxidation) to ~0.7 (pure fat oxidation). At the completion of the study, Phinney's elite cyclists displayed a mean RQ during testing at 60-65% VO2max of 0.72 - very darned close to 0.7![2] In other words, the cyclists were as fat adapted as they were ever going to be!

Another study by Helge and co-workers found that 7 weeks on a low-carb diet produced much less improvement in cycling performance than a high-carb diet[3].

To anyone intimately familiar with the metabolic demands of glycolytic activity, the findings of the above studies will come as no surprise. No matter how fat-adapted you become, glucose will always remain the primary energy source during sustained, high level exercise. The reason glucose is utilized as the primary energy substrate during high-intensity activities like sprint cycling is because fatty acids simply cannot be broken down fast enough to replenish ATP (the ultimate cellular energy source).

Furthermore, the findings of Phinney and Helge suggest that fat adaptation may actually impair the delivery of glucose to working muscles during glycolytic activities!

Does this mean you have to give up your low-carb diet if you wish to restore your performance during spin classes?

No way!

Despite the highly-polarized and often hostile sentiment that exists between low-carb and high-carb advocates, nutrition isn't an 'either-or' affair. There is absolutely nothing to stop you from utilizing a strategy known as 'carb-cycling'. While carb-cycling gets little mention in popular low-carb diet books, many athletes and bodybuilders have been utilizing it in one form or another for decades.

There are numerous ways to approach carb-cycling; I'll outline what I have found to be the safest, most convenient, and most effective form. It involves taking a large serving of carbohydrates in liquid form immediately after you finish your training. The period that immediately follows a glycogen-depleting workout is a unique one, especially the first 30-60 minutes. During this time, any carbohydrates consumed are preferentially shuttled straight to the muscles where they are used to restore glycogen. Contrary to popular mythology, post-workout carbs do not lurk around in the bloodstream causing damage, they are not converted to fat, and they do not suppress growth hormone release.

The amount of carbohydrate you consume after training depends on the type and duration of the activity. I thoroughly explain the science of post-workout nutrition in my new book The Fat Loss Bible, and I give full details on how to calculate your post-workout carb intake.

However, to get you started, I would suggest you begin drinking 75-150 grams of carbohydrate in liquid form, along with either 30-40 grams whey protein and/or 6 grams of a powdered amino acid formula that is rich in branched chain amino acids, immediately after your spin classes. It is important that you utilize both carbs and protein/aminos after training. Suitable forms of carbohydrate include maltodextrin (a.k.a glucose polymers) or rice syrup, diluted in around 500 ml water. You can add a little glucose or honey to sweeten the mixture. I recommend liquid carbohydrates over solid carbs because the former will be assimilated much quicker; remember, post-workout the goal is to get glucose to the working muscles as quickly as possible.

After finishing your post-workout drink, hit the shower, head on home, and then eat a solid meal when hunger returns or within 2 hours of finishing your class (whichever occurs first).

Try this, and I'm sure you'll be amazed at the difference this will make to your spin class performance!

All the best,

Anthony Colpo


1. Phinney SD. Ketogenic diets and physical performance. Nutrition & Metabolism, 2004; 1:

2. Phinney SD, et al. The human metabolic response to chronic ketosis without caloric restriction: preservation of submaximal exercise capability with reduced carbohydrate oxidation. Metabolism, Aug, 1983; 32 (8): 769-776.

3. Helge JW. Adaptation to a fat-rich diet: effects on endurance performance in humans. Sports Medicine, Nov, 2000; 30 (5): 347-57.

Special THANKS again to Anthony Colpo for his typical thorough and well-documented response to my reader's question. If you would like to learn more from him about his recommendations while engaging in intense fitness training, then be sure to check out The Fat Loss Bible for yourself. ENJOY!

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Blogger Pot Kettle Black said...

That's good stuff.

Now, question: If I'm losing with a ketogenic diet, will this infusion of carbs kick me from ketosis? That seems like it would be sub-optimal. Would like some further insight. Perhaps the Fat Loss Bible.

Ultimately, I suppose it talks to specific goals as specific times. If it's burn fat, maybe muscle fatigue is part of the trade off. If it's build muscle, then I don't see an alternative.

Thanks Jimmy and Anthony.

8/09/2007 8:11 PM  
Blogger Jimmy Moore said...

Anthony does address that in his new book, but I'll see if he will answer it. THANKS PKB!

8/09/2007 8:30 PM  
Blogger CJaneWinn said...

Fabulous information, and with what I am familiar with regarding human physiology and cellular respiration it all makes perfect sense.

pot kettle black, I'd think with the muscles using the glycogen quickly after an intense workout that it probably wouldn't kick one out of ketosis, but that's just my guess...let's see what Anthony has to say.

8/09/2007 9:08 PM  
Blogger Jimmy Moore said...

Kamran sent the following comment:

To the comment above, ketosis is a very catabolic state, and Anthony Colpo, being one of the biggest advocates of low-carbing, says that.

KETOSIS IS WAY OVERRATED. Reducing carbohydrates to a level where one is still above ketotic levels, is the most optimal way to lose fat and preserve muscle.

8/10/2007 8:11 AM  
Blogger jm_funk said...

I've actually been thinking about emailing you a similar question. Loved Colpo's cholesterol book so much, I have both the physical and ebook for quick searches. Will definitely buy the new one.

I've lost 70 pounds doing lc (100 long term) and road cycling (used to do spin). I've never had the fatigue (or at least willed through it). Last saturday I rode 30 miles in Florida heat after breakfast with no problems. My problem is that for the last 6 months I've been on a plateau. I bought the Tanita Ironman Scale to measure everything. It shows that the weight I lose is muscle and then I gain it back. It just seems to be a fluctuation of muscle, fat much less so.

I have been trying to figure out the cause. Do I need more protein, more sleep, less calories (haven't changed diet) or less pseudo stuff (CarbSmart ice cream, splenda, Chocoperfection, my daily Jack Daniels) even though none of this has changed. I ride about 100 miles a week. I don't really need to gain muscle just want to keep losing fat (currently between 23-24%, 6'4", 250lbs).

Any help would be appreciated, if not maybe I will find it in the book.

Thanks, Joe

8/10/2007 8:38 AM  
Blogger Science4u1959 said...

More pearls of wisdom. As always Colpo provides a wealth of quality information. This is indeed good advice for those that participate in high-intensity training. Speaking for myself: I don't need these post-workout carb-cycling techniques, as I hardly ever experience severe muscle fatigue - probably because I'm the laziest guy on this forum - although I do consider backpacking 30-50 kilos of cameras, lenses and assorted gear on wildlife photography treks a reasonable workout :)

8/10/2007 8:47 AM  
Blogger katherine said...

Awesome, thanks for this post Jimmy! I've been low carbing for about 3 weeks now, and started Thai boxing at the same time. My body was really, really craving some carbs after a crazy workout last weekend that left me exhausted, so I had a non-low carb protein shake with some berries and honey...this let me know that I was actually doing something right! I am definitely going to get his book!

8/10/2007 9:15 AM  
Blogger mrfritznyc said...

the thing is, except for competitive athletes and lunatics, nobody needs to be doing any activity that drains you to the point that you need to "carb cycle." Do some strength training, lifting heavy weights slowly to failure, low reps, 1 set only, cut the carbs and don't overeat. You'll get where you want to be-slim, fit, and strong, just as fast, without all the damage done by all that high volume lifting/excesive cardio.

mrfritznyc, aka "the pig headed mrfreddy"

8/10/2007 10:37 AM  
Blogger Pot Kettle Black said...

Jimmy, CJane, thanks.

FWIW: today, post lifting, I had a couple of eggs, some cottage cheese, a SF energy drink and sport beans. If I recall correctly, jelly beans have very fast absorption of the sugar (I think in the atkins book I have it was like 91 compared with table sugar being 100). It's not the 80+g that Colpo is talking about, but I figure we can work up to that and monitor. Nothing to report yet, but I dunno that I but Kamran's sentiment. Since recommiting to Atkins level carbs and rekicking my ketosis, I seem to have lost a few pounds, but kicked up my LBM. If it's catabolic, it's catabolic in the right places.

8/10/2007 12:03 PM  
Blogger joycen said...

I have been on a low carb diet for four years and spinning 4 to 5 times a week where my heart rate is between 75% to 85% and light weight lifting. I have been tired but I thought it was just because of how much I have been doing. I probably am around 75 to 100 carbs a day. Does this give me enough to not feel this muscle fatigue? If I take the carb/protein drink that Anthony talks about will I find a significant increase in my muscle building? Maybe I need to buy his book. Thanks.


8/10/2007 12:25 PM  
Blogger Charles said...

I agree with the "ketosis is way overrated" comment. I don't think I spent much time in ketosis during my weight loss at all.

I don't disagree with Anthony Colpo's view of fatigue, but I have also found that these symptoms happen when an athlete overtrains. Those cyclists in Dr. Phinney's studies were highly trained. New low carbers can't make that claim, and once they get the initial energy boost, they may tend to overdo it because it's the best they've felt in years. I certainly add whey and casein after workouts to speed recovery, but you also have to listen to your body and back off when you get that fatigue feeling that just won't go away. Sure, maybe you can't immediately repeat the hard efforts of guys on a sugar-high, but I believe you can make up for that with intelligent training.

Make sure you're getting plenty of sleep and ensure you're getting enough recovery between workouts. Many of the great running coaches, like Bowerman at Oregon, were big on hard/easy workouts, and many new marathon training programs like FIRST, encourage quality over quantity so it gives the athlete time to recover before the next hard workout. Elite athletes rarely train over 75% VO2 Max and studies show that fat adapted athletes leave much of their glycogen levels intact after exercise.

I don't know about cyclists, but we runners tend to think that if we train harder and harder, it will automatically result in greater performance and this isn't always the case. As Gordon Pirie writes in his book, "more and more intervals with less recovery time will turn a champ into a chump."

Again, I'm not disagreeing with Mr. Colpo, but I've also experienced overtraining and the symptoms are awefully similar. I've also found that I can reproduce and even increase my running performance as long as I give myself adequate recovery time.



8/10/2007 3:02 PM  
Blogger Sue said...

I think we were never meant to exercise so hard and for so long. I'll keep my exercises at low intensity so I don't need the extra carb. It makes perfect sense that athletes would need carbs after a workout when they work to a level that is depleting their glycogen supplies in their muscles.

8/13/2007 2:38 AM  
Blogger Pot Kettle Black said...

Some thoughts:
1- I was a lot less sore from my workout on Friday after adding 25G of post workout carbs. It didn't seem to affect ketosis or loss or anything really, but I didn't feel sore all over all weekend. Experiment being repeated today.

2- On further reflection (and comment reading), I suspect that Mr. Colpo's recommended levels of post work carb are high for the average LC dieter/exerciser. Since 25g (plus the normal milk sugar in the cottage cheese) seemed to fix what was ailing me, it might be that 25g is closer to optimal, at least for me. Time will tell something closer to the true story.

3- Re: Sue: "I think we were never meant to exercise so hard and for so long." I read protein power and other paleo sites and they suggest feats of "superhuman" strength and endurance by our ancestors who were pretty much the same as us. I find these somewhat incredible, but at the same time, I think we were meant to hunt with tools that didn't include projectile weapons like guns and bows. That would involve running, cunning, and/or some brute clubbing. So, I dunno what the optimal level of exercise is, but its probably closer to "so hard and for so long" than "not at all." Course, I currently do 14 exercises, none more than once a week, spread out over 5 workouts, so I'm not doing as much as many.

4- As always on the good stuff, Thanks Jimmy and company.

8/13/2007 9:41 AM  

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