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Pain Equals Potassium by Brian MacKenzie - CrossFit Journal

Pain Equals Potassium

By Brian MacKenzie

Video Article

Oh the burn!

At some point during Karen, your quads start to tingle with a certain familiar sensation that can only be described as “burning.” As you work your way toward your 150th toss of the Dynamax ball, the feeling gets worse and worse until you heave the final ball to the wall.

We all feel lactic acid building up during a workout. Or do we?

It turns out the burning sensation actually comes from the accumulation of potassium outside the cellular wall. Lactic acid, more specifically lactate, plays a role in this process, but mounting evidence suggests it’s actually a fuel rather than the substance responsible for soreness.

The following video features Brian MacKenzie of CrossFit Endurance explaining the science of soreness and performance.

6min 35sec

Additional reading: Why You Should Sprint Train by Tony Leyland, published May 1, 2007.

Free Download


46 Comments on “Pain Equals Potassium”


wrote …

Excellent Information! We need to get this stuff - this type of info and training to our Olympic Marathon guys!


wrote …

so why are no crossfiters competing and winning at the elite endurance level? they have the aerobic capacity AND the strength component?

you say that the missing link to elevated elite performance is not found in sport specificity, yet you have not produced any sport specific elite endurance athletes using the generalist approach.

maybe instead of saying that this is why the elite community is wrong, maybe you should say, this is the science to how a generalist can be a generalist and complete longer events.


wrote …

Great video. More endurance stuff would be great.


because they're obviously gonna lose to the top guys who specialize in endurance events. but a good Crossfitter will be better in nearly every other area of fitness


wrote …

World Record for 5000m (5 Km) on the track is 12:37 by K. Bekele. Most world class 5K runners are presently knocking out 12:50's - Mack, that is 5K NOT 10K!
I also think it overly simplistic to claim that the muscle pain experienced is solely due to Potassium - No one really understands the extent and role of free radicals produced at this level of work. I don't think the Crossfit world has experienced an athlete yet who has achieved or been able to sustain a comparative work load of that calibre. By that calibre I mean a world class 5K runner, World class cycling time trialist, world class 400/800/1500m swimmer, world class single sculler (rower). The "sport" is still too young and just exploring its boundaries...


wrote …

I disagree.

It is the build-up of H+ ions, produced by glycolysis, that reduces he pH within the muscle from a normal 7.1, to the beginning of the "burn" at 6.5 and progressively worse as you go below and continue the effort.

"The breakdown of glucose or glycogen produces lactate and hydronium ions - for each lactate molecule, one hydrogen ion is formed. The presence of hydronium ions, not lactate, makes the muscle acidic that will eventually halt muscle function. As hydrogen ion concentrations increase the blood and muscle become acidic. This acidic environment will slow down enzyme activity and ultimately the breakdown of glucose itself. Acidic muscles will aggravate associated nerve endings causing pain and increase irritation of the central nervous system. The athlete may become disorientated and feel nauseous."


wrote …

Guys, I'm not sure if I follow this (so please correct me). I eat Potassium rich foods (like almond butter and sunflower kernels) before and after work outs to avoid muscle soreness and DOMS. This seems to be working very efficiently for me.


replied to comment from Josh Cline

"so why are no crossfiters competing and winning at the elite endurance level? they have the aerobic capacity AND the strength component?"

That's comparing apples to oranges. What would really be telling is if some currently elite endurance athletes fully adopted Crossfit training, then see what happens to their performances over time.


replied to comment from Kim Pedersen

Potassium, protein, and carbs are all needed. I would be curious to know how many people here take isopure. Such a magnificient protein. When I skip out on the isopure which is high in potassium I am usually miserable the next day to a point that even serious foam rolling is worthless.


replied to comment from Christopher tucker

Yeah i would be curious as to a proposed physiological mechanism for why potassium ions building up in extracellular matrix would be noxious


wrote …

I was under the assumption that the reason you puke is because you have reached a level of acidity in your blood from high CO2, and lactic acid concentrations, to the point where your body can no longer buffer it. Therefore your body in an acidosis state has to find a quick way of getting rid of acid; and dumping the HCL acid in your stomach is an easy way to free up more of your body's buffering capacity and steer your body back to narrow PH of 7.34-7.35. I too would like to find out how potassium comes into the picture.


Josh, I suspect that the difference has to do with the fact that WR holders in most endurance events do not typically train for any other type of challenge, so they are unburdened by the weight of musculoskeletal development beyond that which is necessary for their specific discipline.


Andy, if you just look at the workload (measured in watts) I'm sure that the top CF competitors are putting out more energy than world class 5k runners. The difference is in efficiency of movement. Top 5k runner weigh much less than top CF competitors and need only move their own body weight using one type of locomotion in one direction. No top 5k runner could create sustain a significant workload when it comes to thrusters or muscle-ups or CF total.

As far as cycling is concerned, guys like Cancellara and Larsson are not small and have respectable leg strength, but every ounce of excess upper body mass makes them measurably slower on the uphills, so they have a negative incentive when it comes to building upper body strength.

Rowers have perhaps a more even distribution of muscular development than any of the other disciplines that you have mentioned, and as such might potentially have the least difficulty crossing over to being competitive at CF events, but the years of technique required to most efficiently convert raw power into speed on the water is likely to keep CF athletes out of the top ranks of sculls competitors. Moving things to Concept 2 rowers evens the playing field a bit, but even there the specialists are likely to retain an edge over the generalists.

The point that I take from all of this is that by training correctly I can be a generalist and still make significant improvements in my endurance capacity. Sure, I might make even better improvements in my 5k time or cycling time trial speed if I only worked on those things, but if I want to do a 30k bike TT in September, Swedish CF nationals in November, 6 track & field events (100m, long jump, high jump, shot put, javelin and 400m) in one night in May and ride 300k in under 9 hours in June, I can't afford to specialize.


wrote …

This is a very interesting subject, I agree with Andy that the sport is still exploring its boundaries. I am currently training for a marathon with 4 CF sessions and 1 long run per week.
So far I feel its going ok but the next 3 weeks is where my mileage will really ramp up and will be interesting to see if my body will be able for it.


Dane Thomas wrote …

[Geek warning]Anybody else notice that he keeps saying "K" when he is talking about Potassium?[/Geek warning]

I know that this isn't Slashdot but I just couldn't resist. ;-)


wrote …

98% of K+ is inside your cells (or intracellular fluid-ICF). K+ is supposed to be inside your cells. The dumping of Potassium to the extracellular matrix can be potent because Potassium controls so many things in the body. As the predominant ICF ion, potassium exerts a major influence in regulating ICF osmolality and fluid balance and for intracellular electrical neutrality in relation to hydrogen (H+) and sodium. Potassium is required for glycogen and glucose deposition in liver and skeletal muscle cells. It also maintains the resting membrane potential, as reflected in transmission and conduction of nerve impulses, maintenance of normal cardiac rhythms, and skeletal and smooth muscle contraction.

Dietary potassium moves rapidly into cells after dietary ingestion. However, the distribution of potassium between intracellular and extracellular fluids is influenced by several factors. Insulin, aldosterone, epinephrine, and alkalosis facilitate the shift of potassium into cells. Insulin deficiency, aldosterone deficiency, acidosis, cell lysis, and strenuous exercise facilitate the shift of potassium out of cells. Glucagon blocks entry of potassium into cells, and glucocorticoids promote potassium excretion. Potassium also will move out of cells along with water when there is increased ECF osmolarity.

Changes in pH and thus in hydrogen ion concentration also affect potassium balance. During acute acidosis, hydrogen ions accumulate in the ICF and potassium shifts out of the cell to the ECF to maintain a balance of cations across the cell membrane. This occurs in part because of a decrease in sodium-potassium ATPase pump activity. Decreased ICF potassium results in decreased secretion of potassium by the distal tubular cells, contributing to hyperkalemia. In acute alkalosis, intracellular fluid levels of hydrogen diminish and potassium shifts into the cell and the distal tubular cells increase their secretion of potassium further contributing to hypokalemia.


wrote …

Is it just me or does anyone else love watching Brian videos? That guy has a lot of good material.


replied to comment from Dane Thomas

In the periodic table of elements, Potassium's symbol is "K". It has an atomic weight of 19 (Hydrogen's the first element, with a weight of "1".)


replied to comment from Josh Cline

Correct me if I am wrong, but Lance A. trained a tremendous amount of intervals and high intensity training. Absolutely not CrossFit, but I think a good example of applying similiar principles to a predominately endurance sport.


wrote …

I myself am a crossfitter but I dislike how this article/video was published with no scientific citations/publishings.


replied to comment from Kim Pedersen


Eating more potassium rich foods won't increase the extra-cellular accumulation. The extracellular K+ results from the work being done. The work would not have happened without potassium. An increased ability to clear it by pumping it back into the cell is what blunts the negative effect.

If your kidney's are normal, you're really not in danger of getting too much K from dietary sources. In fact, I'd say a good number of people don't get enough.

And yes, we do deplete potassium. Since it's needed for a host of functions (see Mark's post above), including muscle contraction, keep eating sources rich in it. You're doing good.


replied to comment from Mark Pinamonti

I'm curious... Is the problem that the potassium is outside the cells, and therefore doing some kind of damage? Or is the problem that the potassium is no longer inside the cells, and therefore cannot perform its normal functions?

And with all of this great and very interesting information (that I used to understand better when I was in school), what do we actually do to gain better performance? Take more potassium (as Kim P pointed out)? Or is there something else in this message that I'm not getting?



replied to comment from James Berg


Many of these claims seem to suggest the POTENTIAL for better performance such as increased lactate threshold, efficiency of Na/K pump, etc. However, there are too many factors at work during a long distance race such as increased body mass due to muscle mass and possibly a lack of comfort in a long time domain. I am not an expert at long distance racing or training, which is all the more reason that I would like to not only see citations for the claim that CFE is superior to long slow distance training, but I would also like to see the athletes that have reaped the benefits at high levels of competition. These presentations lack the data that Crossfitters are supposedly so adamant about to carry any real significance. I realize that its not necessary to discuss the minutiae of the physiology that goes on, but it has to be grounded in some kind of data or else it's just a guy talking (albeit a very smart guy).



wrote …

Yikes. I'm with James Berg on this one. If one is going to venture into explaining the exercise physiology/biochemistry black box then PLEASE make sure you provide complete, accurate and cited information. Temporary Na/K pump dysfunction and ion imbalances might be associated with muscle fatigue but it is FAR more complex than has been presented. Yes lactate is a fuel but "Lactate retards the acidosis process"?!?! Huh? Any undergrad ex phys student could correct him on that one! Intense training is having numerous effects on the body, far more than just on the Na/K pump!!!

I was once considering taking the Endurance Cert but seeing that vid makes me reconsider. I'm sure Brian is an excellent coach and very knowledgeable and this was only a short clip of a lecture but CFJ you need to do better than that! Maybe stick to the CrossFit mantra of staying away from explaining the black box and sticking to measuring results only? Simpler and easier for everyone.


replied to comment from Brian Ross

Yes, Lance Armstrong trained a tremendous amount of intervals, but he also trained a tremendous amount of long (not necessarily slow ;-)) distance where he was riding for more than 6 hours a day. That is decidedly not Crossfit-like. Intervals have always been a part of a serious cyclist's training, as has hill-riding, which is a kind of forced interval in a way.

I don't see how Crossfit endurance will ever really dominate endurance events. But I wouldn't expect it to dominate powerlifting, either, and there's nothing wrong with that. If you want to train and compete in both endurance events and powerlifting, Crossfit is the way to go, but if you're looking to specialize, there are plenty of good tidbits to get from Crossfit, but most of your training should be in that specialty, right? If I know I'm going to be in a 50 mile bike race in 2 months, I'm going to ride my bike enough to be prepared.


wrote …

I read an article givin to me by my Biochemistry professor about the possibility of Ca+ pumps being the cause of muscle failure and and also DOMS. Since no one else here is citing their sources I will follow suit. It described a study where cyclists rode vigorously for three days in a row to bring about DOMS. Snippets of their muscles revealed elevated levels of Calcium in their muscles cells compared to levels with fresh legs on day 1. This was attributed to Ca+ pumps in the muscles cells. When these pumps release Ca+ in muscle cells, the muscles contract. Repeated cantractions of the muscle cells forces the pump to continually open and close. Eventaully these pumps loose their ability to fully close, leaking Ca+ ions in the muscles cells. When the muscles can't tell the difference between higher and lower levels of Ca+, the muscles cannot contract when called upon; muscle failure. To me, within this context, this whole argument is null because the body's ability to withstand muscle failure and also avoid DOMS with higher and higher levels of capacity is dependant on the Ca+ pump in the muscle cells ability to withstand leaking. Obviously fitter people can do more without their muscles failing or having DOMS the days following. The ability to withstand work capacity is synonymous with the ability to avoid Ca+ leakage in the muscles cells. So what are we talking about? Well obviously research has not definitevely proven any of the above reasons for muscle failure within excercise physiology: higher [H+], lactic acid, [K+], nor [Ca+]. Just somemore gristle to chew on. The study I refere to actually started studying Ca+ in the heart muscles of people whom suffered cardiac arrest. They discovered the leakage of Ca+ in heart muscles because of muscle failure (cardiac arrest), and continued on to the study with the cyclists.


wrote …

There is way too much conjecture in the video and the comments. "Trust me, I'm right" is not a convincing argument.

It's one thing to argue that a certain thing works but you don't know why (Black Box model). But it's entirely different, and useless, to argue why without proving it.

With an undergrad degree in kinesiology and currently studying medicine, I would love to see this video and conversation expanded and explored in much more detail. Unfortunately, I won't/can't comment because the substance isn't there.

If pain is potassium, why aren't hyperkalemic patients in agony?


wrote …

I am a biochemist and I got my source straight from my brain and word for word from Understanding Pathophysiology 4th edition(Huether/ McCance)because I didn't want to get anything wrong. Sorry for not citing my sources earlier.


replied to comment from Mark Pinamonti

Appreciate that but your post doesn't really talk about potassium and exercise, just potassium's role in general. Unless I'm not connecting the dots...


wrote …

Also, It is NOT an increase in function of the Na+ K+ pump that is causing this outflux of K+ to the extracellular fluid. If you will read my post from above and put two and two together:

"Insulin deficiency, aldosterone deficiency, ACIDOSIS, cell lysis, and STRENUOUS EXERCISE facilitate the shift of potassium out of cells.

During acute acidosis, hydrogen ions accumulate in the ICF and potassium shifts out of the cell to the ECF to maintain a balance of cations across the cell membrane. This occurs in part because of a DECREASE!!!!! in sodium-potassium ATPase pump activity. Decreased ICF potassium results in decreased secretion of potassium by the distal tubular cells, contributing to hyperkalemia."

-Understanding Pathophysiology, 4th edition page 109 (Alterations in Potassium and Other Electrolytes

BRIAN: you said K+ shifting out of the cell (acidosis during strenuous exercise) was due to the increased activity of the Na+K+ pump! This is wrong information!


Brian MacKenzie wrote …


replied to comment from Brian MacKenzie

Thanks, Bmack!

For others, from the discussion of the article:

"These observations suggest that speed endurance training is a powerful stimulus to improve performance even in an event lasting >30 min despite that the duration of each exercise bout was 30 s. In our previous study (31), which also examined the effect of speed endurance training, no change in 10-km performance was observed, but in that study the amount of training was reduced by 80%. Apparently, maintaining some aerobic sessions with high-intensity running, together with the speed endurance training, played a key role in causing the better performance in the present study. This is the first study to show increased long-term performance in endurance runners with a reduced volume of training and speed endurance training."

Goes on to re-enforce that intensity is more important than amount, and say that the lower potassium levels are likely due to an increase in the number of Na+-K+ pumps (alpha2-subunit).


wrote …

If you don't have a science background, this abstract is easier to understand...


wrote …

For those incredulous about lactate as a buffer:

It's a bit tedious to get through. The gist is that at higher intensities, lowered pH is buffered more than would be expected by the usual suspects [at lower intensity, the "usual suspects" are sufficient]. So, there has to be something else available that needs protons in order for the math work. Proton production happens at earlier steps in the whole process than does lactate production. So, the earlier steps "donate" H+ to the production of lactate, which, apparently increases pH (I've got to go back to get clear on why that is) and exactly accounts for the above discrepancy. That's a rough summary of a lot of stuff. Read the link to geek out if you want.

New stuff is discovered all the time. Mistakes, miscalculations, and just flat out new findings. The assumption that Brian just makes this stuff up is pretty silly. I always think, "damn, I learned something different, what am I not up on?" If you doubt it, that's cool, but google a little first before shouting heresy, and/or dismissing the material.


replied to comment from Brian MacKenzie


This research article supports the use of a taper in order to peak a performance which has been known and used by almost every running coach and athlete for decades. This study does not provide any evidence that it is a build up of potassium creating that "burn" sensation, it only uses 17 participants whom are split into two groups and by their times they are beginner runners who would adapt to almost any training stimulous.

I'm disappointed.


wrote …

When/where have you ever seen a 9 week taper recommended?

If these are beginners, why didn't the control group make any significant gains over a 9 week period of continued endurance training at 55k/wk if they would adapt to "almost any training stimulus"?

Maybe the magic of a traditional taper has little to do with the high volume preceding it and every thing to do with the dose and type of stimulus it provides.


wrote …

The LDH step, production of lactate, uses a proton, buffering the accumulation of positively charged ions.

My question is if we know this to be true, then why are not more people using a pH threshold test instead of the 'old school' lactate threshold test?


wrote …

I always love to learn new things, I had read an article a while back with regards to muscle fatigue... not necessarily "burn". But it talked about "Calcium Leakage", which this article made me think about.

Quick Google search

Would there be correlation between the two?

While CrossFiter's are just that "Cross Fit", I would also say aside from the chemical aspect you are also looking at two different muscle types(I & II) which make a difference. Perhaps that is the conditioning aspect though.


Rob Barrese wrote …

Good Stuff B Mack... thanks! Maybe some of the commenting folks will make it to a cert and get a better understanding of what you are talking about? OR maybe they like the distance of a computer to pop off at the mouth?

Anyway, great stuff. Hope to see more of your video's.


wrote …

Always wondered what the phys was behind the sickness/weakness one feels doing these WODs. Totally different experience than the fatigue of an LSD training day. Running is a weakness for me, have not found the right approach to address it ... yet.



Since this is all pretty much conjecture...I would say, both the increase in extracellular K+ and the nausea are caused by global cellular hypoxia. Very high intensity exercise requires so much of the body's fuel (think substrates, increased blood flow to the involved muscles) that an relative shock state is produced. An oxygen, substrate and, ultimately, ATP debt is created.

This ATP debt could cause ATPase Na-K pump failure, K+ accumulates on the outside, but more dangerous, Na+ stays inside. This Na sucks fluid into cells, cells swell to the point of breaking open, releasing myoglobin, leading to rhabdo. This is one of the possible causes of rhabdo in exercises. This physiology follows the mechanism seen in heart muscle during an MI.

Additionally, as blood flow gets shunted to the working skeletal muscles, less goes to the brain and gut. Both cerebral and gut ischemia (due to the shunting of blood away from these organs) are pro-emetic. I do not think LSD (overdistance is a better term) creates enough of a global oxygen debt to cause this gut/cerebral ischemia.

Anyway, that is my 2cents,



replied to comment from Ian Bonesteel

Yes, I read that same article. I didn't see your comment when I posted mine with a couple of links. Definitely interesting stuff.


replied to comment from Andy ORourke

At #5, I am not exactly sure how you classify "world class". For example, in my opinion, if you qualify for NCAA Division I Swimming and Diving Champs, you are close to "world class" in that specialty, considering it is the toughest single meet to qualify for in the world (significantly harder the U.S. Olympic Trials). In this context, there are altheletes of this caliber floating around in the crossfit community.


wrote …

I have a question.

I understand the concept of CrossFit, fully support it, and am always trying to learn more about nutrition and physiology both in school and at home. Is there any way that potassium in one's diet could effect this? I'm sure this sounds like a dumb question and I just don't get it, but it seems like there would be a correlation between diet and fitness in this case.


wrote …

Sorry, guys, I'm just a police academy instructor and have no big letters behind my name, but the deep discussions about post workout vomiting and potassium have me blinking in confusion. Forgive my over simplistic thinking, but 1) hypoxia causes nausea. 2) overheating causes nausea. 3) stress (physical and mental) causes nausea. 4) insufficient perfusion (shock) causes nausea. How is it that an intense workout, which can bring about all the above to one level or another, can cause really smart people to discuss the causes of vomiting? I'm sure some supergenius out there with the whole alphabet behind his name can slice my thinking to ribbons, but from what I've seen and experienced it's nothing more complicated than that. Thanks and good workouts.


replied to comment from Christopher tucker

Haha, incredible response! Finally someone that follows the science behind the performance!

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