The Concurrent Training Effect Blog #3

To read the first two installments please see the ALN blog page here:

The Concurrent Training Effect Blog #3

As noted in our first installment, the concurrent training effect is a mitigation or cessation of the hypertrophy response to strength training when both strength and endurance training are performed concurrently.  Now that we understand mTORC1 (from blog #2) is almost exclusively the driver of strength training induced hypertrophy we know that looking into how endurance training can influence it is the key to insight into how to mitigate the concurrent training effect and thus to creating a superior CrossFitter or hybrid athlete.


In this blog we are going to seek a better understanding of how endurance training can effect mTORC1.  The molecular effects of endurance training on hypertrophy are much more equivocal than the molecular effects of strength training.  There is no single molecular source for the manner in which endurance training can or does effect hypertrophy.  This blog will focus on those sources most generally accepted to have the greatest impact.

We will begin with AMPK (adenosine monophosphate activated protein kinase).  Endurance training of sufficient intensity results in metabolic and molecular responses that activate AMPK.  AMPK has been shown in animal studies to be able to inhibit mTORC1.  In humans its effects on mTORC1 are less certain, but overall the scientific consensus is that it (a specific form of it) likely contributes to the concurrent training effect.

Our next focus is on the sirtuin family of NAD+ dependent deacetylases with SIRT1 being of primary interest.  In the previous paragraph it was noted that the intensity of endurance exercise is a controlling factor in AMPK activation.  The same is true for SIRT1.  The presence of SIRT1 has been clearly demonstrated to inhibit mTORC1, thus the effects on mTORC1 of relatively frequent intense endurance training may due fully, or in part, to SIRT1.

The final possible metabolic cause of the effect of endurance training on mTORC1 to be covered in this blog are unfolded proteins.  Intense and frequent endurance training and high fat diets are both triggers for unfolded proteins.  The body’s response to increased unfolded proteins includes the blocking of protein synthesis via a decrease in mTORC1 activity.

Hopefully you have already noted the fact that the intensity and frequency of endurance training are catalysts in each of the above possible metabolic pathways in which endurance training can effect mTORC1.  This fact will be the focus of our next blog when we take the information from the first three blogs and use it to propose specific training protocols which can mitigate, and even nearly eliminate, the concurrent training effect.

The Concurrent Training Effect Blog #2

This 2nd edition of The Concurrent Training Effect blog is going to focus on the molecular underpinnings of skeletal muscular hypertrophy.  Understanding the driving force behind the molecular response to strength training can provide us insight into why concurrent strength and endurance training can negatively affect muscular hypertrophy and strength.  In addition, a better understanding can lead to ways to mitigate the effect and optimize progress.  If you are a CrossFitter, or any other form of hybrid athlete this blog is for you.  Keep reading…

Mike Mentzer - knew a thing or two about muscular hypertrophy.
Mike Mentzer – knew a thing or two about muscular hypertrophy.

A Very Cursory Overview of the Science:

The currently agreed upon molecular key to skeletal muscular hypertrophy is the mammalian target of rapamycin (mTOR).  mTOR exists in two complexes with mTORC1 as the type associated with muscular hypertrophy.  mTOR is most commonly activated via growth factors, but with strength training its activation is executed in an entirely different fashion.  An unknown kinase gets activated causing a chemical cascade resulting in the potent stimulation of mTORC1.

Mechanical kinase activation is the not the only manner in which strength training stimulates mTOR.  We have all heard of the post-workout anabolic window for nutrient consumption.  The following molecular explanation is THE reason the post-workout window has been so widely touted (and misrepresented equally as often) in the fitness world.

After an intense training session (and for several hours) the skeletal muscles pull a significantly greater amount of the amino acids leucine and glutamine from the blood.  The leucine individually is a potent activator mTORC1 and augments the previously mentioned kinase based mTORC1 activation.  The increased glutamine yet again enhances this synergistic effect as the resultant transport of glutamine out of the muscle further up-regulates leucine intake.

Start and Finish provide both leucine and glutamine (as well as other great stuff).
Start and Finish provide both leucine and glutamine (as well as other great stuff).

The Bottom Line

Bottom line, and there is a lot more to it than described here, the end game for strength training induced muscular hypertrophy is it is almost totally dependent on mTORC1.  One can thus reasonably deduct that endurance training can somehow blunt mTORC1 activation, and or its ability once activated to execute its normal spike in protein synthesis and the resultant muscular hypertrophy.

The next installment of The Concurrent Training Effect blog will focus on the manner(s) with which endurance training may effect mTORC1.

ALN Concurrent Training Effect Blog Installment #1

Joan Rivers used to say, “Can we talk?”  So, can we talk?  I want to “talk” to you in this blog about something very important to anyone interested in complete fitness (CrossFitters, this means YOU), and that is building strength and endurance simultaneously.

Simultaneously training for both strength and endurance can (and will to some degree) result in the inhibition of the body’s ability to adapt to either stimulus with the greater inhibition seemingly focused on the hypertrophy response to strength training.  This is known as the concurrent training effect.  Until fairly recently this effect was generally misunderstood in the fitness community.  Most trainers, coaches, and trainees thought that simultaneously training for strength and endurance would pretty much negate the strength training results.  In other words, they thought the concurrent training effect was absolute.  It isn’t, and the balance of this blog is going to be a chronicle of my research into the concurrent training effect.  As I learn so will you…

CrossFit competitors who have significantly above average strength and endurance.
CrossFit competitors who have significantly above average strength and endurance.

In my opinion, the advent of Greg Glassman’s CrossFit has done more than any formal research to change the fitness world’s concept of what can be done in terms of increasing all aspects of fitness simultaneously (even beyond strength and endurance to things like skill development).  CrossFitters have shown that you can become bigger, faster, stronger, AND dramatically increase your strength endurance and endurance.  I would say that one of the best examples from the CrossFit world of how much the concurrent training effect can be mitigated is a woman named Tia-Claire Toomey.  She has placed second at the CrossFit Games (a massive test of all things fitness related) and made the Australian weightlifting team which competed at the 2016 Summer Olympic Games in Rio just two weeks after the CrossFit Games.  She performed better at the CrossFit Games than the Olympics in terms of placing, but the fact she was able to compete at a very high level in both CrossFit and weightlifting is a testament to what can be done in terms of building strength and endurance simultaneously.

My research will begin with examining adaptation to both strength and endurance training at the molecular level.  Don’t worry, this blog is not going to turn into a science blog, but the bottom line is that it is only a minor flub to say it all starts at the molecular level and if we can understand that, in only the most cursory sense, we can gain a much deeper understanding of how to optimize performance when simultaneously training for both strength and endurance.

Watch our page on Facebook and the blog on for the 2nd installment of the ALN Concurrent Training Effect Blog.

Chris Mason
Owner AtLarge Nutrition, LLC

Your author and his bae :).
Your author and his bae :).