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Magness Speaks — Crossfit Endurance, Tabata Sprints, and Why People Just Don’t Get it

 High Performance West Elite athlete,  McKayla Fricker . 

High Performance West Elite athlete, McKayla Fricker

Not terribly long ago, I stopped dating a girl because she did crossfit.

Okay, it wasn’t the only reason, but it was a major factor. I mention this not to show how messed up my dating life/requirements may be, but to show how strongly I feel about the marketing scheme that is Crossfit.  I’ve always wanted to write a blog post about it, but the article in this months Runner’s World has finally pushed me over the edge.  I’m writing this blog to give a 2nd opinion and to combat the marketing hype that surrounds crossfit.  I wouldn’t take much offense to crossfit and would let it do its own thing, except when you start telling people that this is the way of the future and that Ryan Hall would run faster if he did this stuff , then I have a problem (Yes, CFE founder has made this claim)

For this post, we’ll focus on Crossfit Endurance because it got some major publication in this month’s Runner’s World and has been getting some hype lately.  If you were at my presentation at the American Distance Summit in North Carolina, you got to hear me take a few jabs at crossfit (and Renato Canova even threw in a jab or two!).  Since it’s a question I get asked a lot, lets take a look at crossfit endurance.

The claim and exploitation

Crossfit Endurance and CF in general is a randomized non-system of training.  It’s basically a set of random workouts that are high intensity circuit based workouts.  In CF this refers to a variety of high strength circuits and in CFE it combines this with high intensity intervals like the famous Tabata “sprints” (sets of 20sec hard/10sec easy).  There are no easy runs.  It’s simply mix short intensity work with slightly longer high intensity work and that’s all you get.

Crossfit exploits a couple different natural reactions people have to get people on their bandwagon.  First, they create a straw man “us vs. them” mentality.  We’ll go over this straw man tactic a bit later, but they try and cultivate this idea that just because it’s different and new means its got to be better.  They throw in some pseudoscience or misinterpretation of science and they’ve bolstered their selling point.  Further exploiting peoples natural habits, they promise better results with less time commitment, which in today’s “busy” world is probably the number one selling point for many products or ideas. If you’ve ever watched late night infomercials, you might start to see some similarities…

Lastly, once you’re in they do something pretty creative.  They first created their own new performance metric on which you’re judged.  Because being good at all the other methods of establishing performance isn’t good enough, so now you’re judged based on some criteria that crossfit develops.  Being a specialist at something is apparently bad?  Additionally, they really go after this hard work/pain = improvement and results idea.  This is also known as the Rocky effect.  But if you’ve been in the coaching business long enough you know that hard stupid work doesn’t get you anywhere.  You can’t just do work that is painful just because it hurts and expect to get better.

Getting beyond some of the basic philosophical tenets of CF that are ridiculous, let’s look at some of their claims in regards to endurance performance and training.

What crossfit doesn’t get

The central claim is that you can get the same endurance benefits (or better) from doing high intensity work and limit any slower to moderate paced running.  They go on to claim that endurance training ages you faster and is detrimental to performance.  Their claim rests on their misunderstanding of VO2max as being equal to or critical to performance.

Let’s use their main research backed claim to look into their claims.

Tabata sprints and the high intensity misunderstanding

A researcher named Tabata did a series of studies on untrained and then moderately trained individuals in which he gave them a workout that consisted of 20sec hard/10sec rest for 4minutes.  When this program was researched, they noted that VO2max increased by a large amount and that certain aerobic enzymes also increased.  Using this and similar studies as their basis, CF has championed the idea that you can get the same, or better, performance off of doing intense work like that done in the study.  Lets use this as a way to look at why these claims are false.

#1) VO2max does not equal aerobic performance

While I’ve written before about the measurement of VO2max and how it relates to performance and you can read more in depth on it in those blog posts, it bears repeating the conclusions reached by Vollaard et al (2009):

“Moreover, we demonstrate that VO2max and aerobic performance associate with distinct and separate physiological and biochemical endpoints, suggesting that proposed models for the determinants of endurance performance may need to be revisited (pg. 1483)”.

The basic idea is that VO2max and performance are separate things.  Just because VO2max is increased or decreased, does not mean that performance will change to the same degree or even at all.  This is a key concept to understand because often times studies will track training’s effects on VO2max and not performance.  For instance, in much of the research cited by CF or even cited in journal articles that talks about the benefit of high intensity training or strength training, they talk about changes in VO2max.

#2) Intervals increase aerobic ability of FT fibers

At the coaching clinic I presented at Renato Canova made a nice point that somewhat fast interval training can increase the aerobic ability of Fast Twitch fibers.  It’s best to think of it as an interplay between FT and ST fibers.  In that different intensities and volumes will increase aerobic or anaerobic enzymes in each type of fibers along the spectrum.  What that means is that although high and low intensity might both hit similar aerobic enzymes, they do so in different ways and in different fiber types.

#3) Why does VO2max improve?

Understanding why VO2max improves is another key to understanding this whole debate.  VO2max does not simply reflect aerobic ability.  Instead VO2max is influenced by several mechanisms.  First off, if you’ve read Noakes central governor or if you’ve read recent research on VO2max testing protocols, you’d know that VO2max isn’t an actual max.  You’re body self limits it.  One way to improve VO2max in a test is to be familiar in pushing closer to that “edge”.  If your body knows you can go there, it loosens the limits a little bit.  Very hard interval training lets the body know it can handle high stress loads.

Secondly, we know that VO2max is influenced by muscle fiber recruitment.  So if we increase the amount of recruitable muscle fibers during a test, the VO2max will rise.  What’s a way to increase muscle fiber recruitment? Sprinting, strength training, etc.  It’s one of the reasons why you see VO2max increases in untrained athletes but not so much in trained following strength training.  The trained ones are pretty good at recruiting more and more fibers as they get closer to fatigue.  The untrained, not so much.

#4) What Happens when we build a base and follow it up with intensity?

A major problem with research studies is that they are all short term.  It’s the nature of the beast.  But let me pose a few questions to all of you.

What does the typical recreational endurance athlete do?

If you answered jog around or do easy and moderate runs with little hard workouts you’d be correct.  Most recreational runners for instance simply go run.  Why does this matter?

What happens when you take people just doing mileage and add intensity?

If you answered they improve over a short time, you’d be correct!  Think back to your HS days when you spent a summer building a base of almost just mileage and then you hit the season and your coach starts throwing interval training into the mix.  You get a nice boost in performance right?  This is essentially what happens in these research studies.  They take recreational runners who just do easy/base stuff and then throw 6 weeks of training hard on them and they improve.  Ask any coach and they’ll say this is just a simple old school peaking/training program. In fact, it might resemble your typical HS application of Lydiard training.

#5) What CrossFit endurance does is reminiscent of training done in the early 1900s

I harp on people to know their history so that they don’t repeat training mistakes.  In the history of endurance training it’s been a constant back and forth between intensity and volume of work. Early on there were very very big swings.  So we went back and forth between training that was almost all easy slow running and that which was all hard interval training.  As training has evolved we’ve gotten closer and closer to that sweet spot and mix.

What CFE has done is ignore all that and try and go back to a time when all that was done was very hard very fast interval work.  It worked to a degree, but performance got much better when we modulated things so that there was a nice mix.

Essentially, Crossfit is living in like the 1940s. We’ve learned from those times and evolved.

#6) A straw man of LSD vs. high intensity

Crossfit, and many others, typically create a straw man where they compare their training to a type of training that isn’t used but by very beginners.  They paint running training as almost all LSD (long slow distance), when the reality is if you look at any elite, college, or high school training program there is a nice blend of volume and intensity.  No one is just jogging around each day.  Yet that is what they have you believe.  This even happens in research when they compare interval training with just jogging around, as if jogging around was the norm for training.

What happens in the real world of course is that there is a nice mixture and blend between volume and intensity.  Essentially, they are arguing for something that doesn’t occur.

#7) Two ways to improve aerobic endurance

In fact, if you look at how some endurance adaptations happen, you can see that to increase things like mitochondrial density, several different intensities trigger similar adaptations.  This goes along with the point on enzyme activity and FT/ST fibers.  But if we look at this nice graphic from Laursen (2009), we can see that two different pathways to achieve some of these functional adaptations are activated by endurance and interval training.  So why the heck would we want to use only one pathway when two different means of getting these nice adaptations are there.  If you just attacked the problem from one side, you’d maximize that side quickly and have nowhere to go!

Additionally, we know that repetitive stress and activation of signaling pathways is what triggers adaptation.  It’s one of the reasons why we train pretty much every day for maximum performance even if some of it is low intensity.  That low intensity easy to moderate work helps to enhance recovery and applies a consistent signal for adaptation.  Pure rest in this case isn’t better (which is often the counterargument).

high intensity versus volume pic.png

#8) Periodization matters

It seems simple enough that people would know that how you plan and periodize training matters.  Training isn’t a random collection of hard exercises or workouts.  There has to be some sort of logical sequence and progression.  If there’s not, then you can expect to get exactly what you trained for, random results.

The bottom line is that so called high intensity interval training (HIIT) which is the new fad word with strength coaches is good.  But for endurance performance it’s even better when it is supported!  You have to support it with something.  Endurance work of various kinds and even pure speed work (with lots of recovery) serves as support for the intense stuff.

#9) Interaction matters

Endurance and strength gains fight each other a bit for adaptation.  While I don’t want to get bogged down in the details, if we look at the signaling pathway for some endurance adaptations and then muscle hypertrophy which are two goals of CF and CFE, we can see that they interact and in fact impair each other in some cases.  For example, doing endurance work right after strength can impair hypertrophy because the mTOR pathway(which signals hypertrophy among other things) is basically switched off with endurance work. This isn’t meant to show that they are mutually exclusive, but instead to show that when you do things matters.  Sometimes a whole heck of a lot!  Thus why you have to think about and plan things, not just do random hard workouts.

This goes for not only sequencing of endurance and strength work, but also in regards to sequencing different strength workouts.  You have to know what pre-fatiguing muscles does to the subsequent training effect.  And you have to know what the effect is on the Central Nervous System.  Crossfit doesn’t think about this at all.  They don’t care.

#11) Individualization

My number one pet peeve.  There is no individualization.  Workout of the day.  That’s the norm.  Beyond that, everyone does the same crap for the most part.  I could go on for days on the importance of individualization, and CF and CFE fail miserably.

What happens in the long term?

Again, I’m going to ask a rhetorical question, for you HS coaches out there what happens if you mess up the balance and do too much intense interval training after that base phase?  The answer is the kids fried.  You see it all the time in High School.  A kid hits the interval training hard, runs some amazing early season times and then fizzles out and is fried by the end of the year.  That’s what happens training wise.  If you want lactate proof, this is what happens aerobically if you mess things up.  You shift the balance to working anaerobically too much (Test #3) and you produce more lactate at each pace, and you are done!

The reason is that there is an interplay between easy to moderate running and intense running or even strength training.  If you work too much on the intensity or strength side you shift things towards that way.  In practical terms your lactate produced at each speed might go up or you might decrease aerobic ability a little bit.  Same goes if you do too much volume with not enough speed support.  You’re speed side would be neglected so that would go down.  It depends on what you are training for but achieving some sort of balance is key.

Additionally, if we look at very long term implications for performance we know that the foundational aerobic mileage does a few things.  First in long term studies on Cross Country skiers, the high volume of training created a fundamental shift in fiber type towards those which improved their performance.  So we got a ST fiber type shift for guys who needed lots of ST.  Secondly, the high volume of training leads to long term increases in efficiency.  Yes, high intensity work or even lifting can do this too but again it’s through different mechanisms.  Lifting for example can increase efficiency via modulating stiffness of the system.  Or essentially creating a stiffer spring.  High Volume training on the other hand works via increase the efficiency of both motor program patterns (because of the repeated nature) and at the muscular level in terms of oxygen utilization and waste product removal.  Again, two different ways to hit the same functional adaptation (improved efficiency), so why would we just want to work on one of them.

So we have research showing that in very elite runners, long term high volume training is needed to make functional changes.  We have practical experience in that throughout history we’ve shifted towards the volumes we do now and that practically every single good runner does a solid amount of mileage (with good intensity mixed in) and we have the theory of why mileage should work.

If we simply put crossfit endurance through the same kind of review we have:
Research- short term studies on high intensity training shows improved VO2max and in some cases performance, but we have looked at why those don’t apply neatly already.  No research on crossfit endurance in particular

Theory - It goes against all known scientific theory for how endurance performance should be improved and how it actually happens.

Practice - No good runners do it.  We know from history what happens and what kind of performance you get even if you do a lot of high intensity work with very little volume.

And lastly, it doesn’t help that they subscribe to every fad from diet to pose method of running that there is.

Finally, if you want a very interesting research approach to the high volume/intensity paradigm read Stephen Seiller’s nice summary here:


And finally, I’d like to point out that finishing and racing are different.  I’ve heard far too many times that so and so did crossfit and finished a marathon so it must work.  No offense and sorry to sound elitist, but if I took off 6 months and did nothing I could still finish a marathon.  It doesn’t mean my program of doing nothing worked.

What does this all mean?

While this was a lengthy rant, it only touches the surface of the Crossfit or Crossfit Endurance phenomenon.  My point wasn’t to critique everything they did (that might be later) but to teach you why some of their claims they make, even research based claims, might be wrong.


Any questions? You can send me a Direct Message on Twitter.  Thank you for reading.| SM

*note: a previous version of his post was originally published by Steve Magness on The Science of Running on Jan. 13th, 2012. It has since been very slightly updated.

Steve Magness