CrossFit and Hormonal Response: HGH, Cortisol and Lactic Acid Response

In exercise physiology, researchers commonly test levels of human growth hormone (HGH), cortisol and lactate threshold.

Some vocab from good ol’ Wikipedia:

Human growth hormone– peptide hormone that stimulates growth, cell reproduction and regeneration in humans and other animals

Cortisol– a steroid hormone, more specifically a glucocorticoid, produced by the zona fasciculata of the adrenal cortex. It is released in response to stress and a low level of blood glucocorticoids. Its primary functions are to increase blood sugar through gluconeogenesis; suppress the immune system; and aid in fat, protein and carbohydrate metabolism. It also decreases bone formation.

Lactate threshold– the exercise intensity at which lactate starts to accumulate in the blood stream.


Now that everyone has the short 101, I first want to discuss how CrossFit triggers the HGH response and why we (everyone, even women) want it.

Vital to athletic development are substantial increases in human growth hormone. Young adolescents secrete Human Growth Hormone at a rate of about 700 μg/day, compared to around 400 μg/day for healthy adults.

Why do we want a large response in HGH?

HGH plays a primary role in several body processes including the body’s growth and repair of tissue, increases in calcium retention, growth of bone, stimulation of the body’s immune system, increases in lean muscle mass, mobilization of fat stores and even the metabolic shift to burning fat as a fuel source. Recent research has also suggested that bone mineralization and skin thickness is increased with a trigger in HGH.

“One study and frequently cited example showcasing the effectiveness of HGH was performed by a group led by Dr. Daniel Rudman, and published in the New England Journal of Medicine. Dr. Rudman et al. showed that tiny amounts of growth hormone injected under the skin produced unbelievable results in just 6 months: lean body mass increased 8.8%, adipose-tissue mass (body fat) decreased 14.4%, bone density increased in the lumbar spinal bones, and skin thickness increased 7.1%. Subjects didn’t change their diet or exercise levels – meaning all of these changes were a result of the growth hormone increase. According to Dr. Rudman, the improvement experienced by these subjects was “equivalent in magnitude to the changes incurred during 10 to 20 years of [reverse] aging”.

How can we get these responses short of injection?

Here are some natural stimulators of growth hormone release:

  • Decreased blood glucose levels
  • Increased blood protein levels
  • Fasting (14 hours for women, 16 for men)
  • Increased protein diet
  • Free fatty acid decrease
  • Stage IV sleep (the deep stage of non-REM sleep in which the body repairs and regenerates tissues)
  • Exercise – especially weight lifting, and especially when done at high power/intensity

Heavy load weight training, short rest between sets, high heart rates, high intensity training, and short rest intervals are all associated with a high neuroendocrine/HGH response.

Weight lifting strengthens joints, increases bone density, prevents osteoporosis, increases muscle mass, improves endurance, decreases insulin levels, and stimulates the release of growth hormone.

CrossFit coupled with a primal diet is WILL increase your Human Growth Hormone levels, meaning you’ll look younger, will have more energy and will be more powerful. “Your muscles will not necessarily become larger (especially if you are female and lack male hormones), but certainly will get denser and more tone in appearance.”


Now I would like to discuss research on CrossFit and the cortisol response and lactate threshold.

Research was conducted on an “extreme conditioning program”. They took the CrossFit workout “Linda,” switched cleans for back squats, and put nine trained men and nine trained women to the task.

Cortisol is a bad guy. Exercise always increases cortisol levels, but you want to keep cortisol as low as possible during rest for optimal recovery.

Lactate and lactate threshold is one of my favorite topics. This phenomenon has been studied intensely over the past twenty years, and unfortunately, we still don’t know very much about it. We now know that lactic acid is a good guy.  We once thought lactic acid was a waste product of exercise and that it led to muscle soreness. Wrong. Now we’re unsure if it has anything to do with soreness. Then we discovered that you can actually make energy from lactic acid. My college professors devoted years of studying this area of exercise physiology and would cringe anytime anyone mentioned “lactic acid” and “soreness” in the same sentence.

The eighteen participants completed a modified “Linda” workout, and then their hormone levels were compared to baseline. Their post-exercise lactate levels were in line with other studies on “high intensity, short-rest” protocols. These lactate levels are somewhat higher than traditional strength training that uses longer rest intervals of 2-3 minutes – with one exception: a 10RM back squat. Apparently no length of rest interval can save you from the burn of a 10RM squat.

Cortisol levels rose after the workout was completed, as they would with any type of strenuous workout. Even an hour after the workout was over, cortisol levels were still higher than baseline. However, after 24 hours cortisol levels had not just returned to normal – they actually dropped just a tiny bit. The researchers pointed out that this means the workout “does not pose an immediate recovery problem in terms of circulating hormone concentrations.”

“These people didn’t die, get injured or require immediate hospitalization. They produced a lot of lactic acid, but no more than if they had worked up to a heavy 10RM squat. The rise in cortisol after the workout was in line with other exercise programs, and participants actually enjoyed a small decline in cortisol the next day. “

Ultimately, CrossFit alone is not the cause of chronic overtraining. It is more likely that too much training in general and poor training decisions is the cause, not the workout, itself.



HGH is your best friend, lactic acid is an ally and cortisol is the enemy. CrossFit and a primal diet can lead to increased HGH for tissue growth and repair and fat mobilization. High intensity interval training can push your lactate threshold farther so you can avoid the “redline” that I’m sure we’ve all hit in a WOD. (“Redlining” is when you want to continue, but are unsure of if you can in-fact pick up the bar without injuring yourself, fainting or losing control of ability to hold in bolus.) Training at these high intensities will increase cortisol like all exercise, but will lead to a DROP in cortisol in 24 hours as compared to other intense exercise protocols.

CrossFit works. I am not in the least surprised at its rapid growth and the addiction that all CrossFitters possess to keep going and get better.

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