“Crossfit is distinctive, if not unique, in its focus on maximizing neuroendocrine response…”

– Greg Glassman

I took my Crossfit Level 1 in the fall of 2012  and while I definitely enjoyed it I distinctly remember feeling annoyed at how much the term ‘Neuroendocrine Response’ was thrown about but never satisfactorily explained.

“Olympic weightlifting and functional movements like the squat and deadlift are more effective than isolation exercises because they elicit a greater neuroendocrine response”

Photo Credit: Sean O'Grady

Photo Credit: Sean O’Grady

..but we didn’t get much of an explanation of what was actually going on other than that  it was

“something to do with building muscle and strength because we release more hormones “

To be fair it was only a 2-day course, there was a lot of content to cover and  its understandable that the course didn’t go into full nerd-level with detail.

Now if you take look at ‘Foundations‘ in the journal it does go slightly more in-depth

“neuroendocrine adaptation” is a change in the body that effects you either neurologically or hormonally

“substantial increases in testosterone, insulin-like growth factor & human growth hormone…[are vital to athletic development]” 

“Heavy load weight training, short rest between sets, high heart rates, high intensity training, and short rest intervals, though not entirely distinct components, are all associated with a high neuroendocrine response.” 


But even still it doesn’t really explain how or why it works. To be fair for a lot of people knowing that Crossfit elicits a higher NE Response and this in turn can lead to better results is enough;  however, as coaches and trainers I think it is our responsibility to actually understand what is going on and not throw the word around. If we want to ‘promote’ Crossfit as a better type of exercise based on the fact that

“functional movements such as squats and deadlifts elicit a greater neuroendocrine response and create better results”

then we had better be prepared to explain what this means.

Hormones 101

As Glassman stated in Foundations, the term ‘neuroendocrine response’ (adaptions) refers to the interaction between our nervous (neuro-) & hormonal (-endocrine) systems, in particular with regards to exercise. Hormones are chemical substances that act like messenger molecules in the body. Now there are A LOT of hormones in the human body, but some of the more crucial ones, when it comes to muscular development and increased strength are

    • Testosterone
    • Human growth hormone (GH)
    • Insulin-like growth factor (IGHF-1)
    • Insulin & Glucagon
    • Cortisol & catecholamines (e.g. norepinephrine, epinephrine)

So lets take a (semi) quick look at each of the ‘key hormones’


Testosterone is produced in the sex organs and is often referred to as ‘the male hormone’ because the development (and maintenance) of several male sex characteristics;  but it actually has an important role in both the male and female body. The level of testosterone produced by our bodies is affected by how much we

    • exercise,
    • eat/sleep and
    • ‘get stressed out’

and the more testosterone our bodies produce the more our bodies will build and maintain muscle and less it will hold onto fat stores.

Human Growth Hormone (HGH) & Insulin-Like Human Growth Factor (IGHF-1)

Produced and secreted by the adrenal glands GH’s primary function is to promote  growth of structures within the body. Among other things GH regulates protein creation, fat breakdown & muscle-building; all of which is mediated/assisted by IGHF-1 (sort of like a mediator)

GH is also associated with appetite control via the production of pancreatic hormones that regulate blood sugar (glucose) levels, and similar to testosterone, ‘optimal’ levels of GH and IGHF-1 depend on whether we have proper

    • exercising
    • sleeping and
    • eating habits.

Insulin & Glucagon

Insulin & Glucagon are pancreatic hormones that controls our blood sugar levels by converting glucose into glycogen for storage when levels are too high (insulin) or taking glycogen stores and turning them into glucose when levels are low (glucagon).

Insulin-Glucacon Feedback Loop

Insulin often gets a bad rep because ‘insulin resistance’ is a condition associated with weight gain, damaged arteries and type II diabetes; but this only occurs when insulin levels are chronically elevated due to unhealthy habits related to food, sleep, exercise or stress.  For most people – unless they have a genetic conditions like type I diabetes – a healthy lifestyle is all they need to keep glucose, insulin and glucagon levels in check.

Cortisol & catecholamines (norepinephrine and epinephrine)(aka the fight or flight and stress hormones)

Norepinephrine and epinephrine  (also known as adrenaline) are released under high-stress “fight or flight” situations in order to ‘prepare the body’ (e.g. increased heart rate, blood pressure, glucose levels etc) to react. Cortisol (a catabolic hormone) is also released when we’re ‘stressed’ and one of its key roles is to  increase blood glucose levels and provide a readily available energy source  should we need to  “fight” or “run like hell”.

Stress Reaction

Unfortunately, the body can’t differentiate between the different types of stress

    • emotional
    • physical or
    • psychological

which means a large portion of the population is walking around with chronically elevated stress hormones. So not only are they constantly ‘feeling stressed’ but also all our hard-earned work is being undone because cortisol can

    • eats away at muscle stores
    • increases appetite
    • slows metabolism and
    • contributing to weight gain.

But wait, doesn’t exercise ‘stress’ the body? and isn’t that supposed to be a good thing? 

Yes, exercise does stress the body and yes it is usually referred to as a good type of stress; however, its important to monitor our training and make sure we recover adequately and take “de-load weeks” otherwise we are doing more harm than good.

So thats  the endocrine portion of the NE response and thats where I’m going to stop for now; but stay tuned for Part II in which I’ll address the neurological component of exercise and how the two work together to create the “neuroendocrine response”.












Marion · March 11, 2014 at 12:31 am

Great article. I was getting concerned about Crossfit putting too much pressure on my endocrine system since I have thyroid problems. My doctor fears that it may “burn out my thyroid”. Great to read some factual info that shows that there are some excellent hormonal benefits to high intensity training that go beyond cortisol. Thanks!

Darrell · September 23, 2014 at 8:47 pm

Awesome post that I now have saved under my book marks for future reference. Thanks for putting all this info together as I’m skimming through my CF Study Guide right now and was just thinking of the same thing about Neroendocrine and decided to do a google search and ended up clicking on your link first. Thanks!!

Wes · October 14, 2014 at 3:32 pm

Thank you for this! This article was extremely helpful in understanding everything more clearly.

Leave a Reply

Your email address will not be published. Required fields are marked *

%d bloggers like this: