High intensity exercise, YES!  This has been the latest trend in workouts, and for good reason. These types of workouts have so so many benefits!

How do you know if you are in ‘high intensity’?

I have definitely seen some (myself included) saying they worked out at a high intensity, but being nowhere close to it.  The surefire way to know what intensity you are in is to get a heart rate monitor.  With your new heart rate monitor on, you will be calculating what percentage of your maximum heart rate (MHR) you are exercising at.  (Maximum heart rate meaning this is around the highest rate your heart can beat at for your age.)  The most simple way to know your MHR is to take 220 – your age.  I am 34, so 220 – 34 = 186 MHR.  The American College of Sports Medicine has another formula, which is supposed to be more specific, but for simplicity’s sake we will use the former.

[col1]Level of intensity







40-55% MHR


55-69% MHR


70% or greater[/col2]

[col3]Physical Cues

No sweating. No change in breathing.

Sweat after 10min. Breathing is deeper & more frequent. Cannot sing.

Sweat after 3-5min. Breathing is deep & rapid. Only talk in short phrases.[/col3]

Neuroendocrine-Immune Responses to Exercise Intensities

Now we wanna get down to the benefits of high intensity exercise, in comparison to lower intensities.  What that big fancy word in the heading means is what does exercise intensity do to our hormonal system and our immune system.  So let’s do another chart (since they’re fun) and then I’ll expand after.

[col1]Exercise Outcomes

Growth Hormone Release

Opioid Response

Nitric Oxide Response

BDNF Release

Insulin Receptor Sensitivity

Immune Enhancement

Oxidative Stress & Risk of overtraining syndrome[/col1]
[col2]Light, Moderate Intensity



⇑, ⇑⇑

⇑, ⇑⇑

[col3]High Intensity








Growth Hormone Release

You may have heard of growth hormone, since it was big in the news at one point with baseball players taking it.  Growth hormone is produced by your pituitary gland and is responsible for promoting growth in children and maintenance (healing) of body tissues in adults.  It also helps to keep blood sugar levels within a set range.  When growth hormone levels are too low, we heal more slowly and our hormones are most likely unbalanced.  High intensity exercise is seen to cause large increases in growth hormone production.  Whereas we do not see the same increases with lower intensity exercise.  Having normal levels of growth hormone will improve immune function, improve brain synapses, increase bone density, promote anabolic (related to growth) metabolism, improves cardiac efficiency, improves recovery, improves blood glucose levels, and increases burning of body fat.  Who wouldn’t want more growth hormone?!  It’s a no brainer.

Opioid Release

It is seen that high intensity exercise increases the release of beta-endorphin peptides.  This same response is not seen with low or moderate intensity exercise.  This increase is responsible for decreases in pain, improvement in mood, and activation of part of your immune system.  We all know that exercise can improve your mood, but high intensity exercise is well above lower intensities.

Nitric Oxide Response

You may have heard of nitric oxide, as it has become a goal of many pre-workout supplements to increase it.  High intensity exercise will increase the response of nitric oxide (you will also see it’s release to a lesser degree with lower intensity exercise).  This will cause an increase in blood flow, specifically with cerebral (brain) circulation, an increase in vascular health, and more nutrients and oxygen going to the cell mitochondria.  All of this leads to tissue repair and more energy.  Wahoo! There is also an increase in muscular contraction and brain performance, so you may feel like you can think more clearly.  However, with high intensity there can be an increase in free radical production will can lead to inflammation and possible injury, muscle wasting, or overtraining syndrome.

BDNF or Brain-Derived Neurotrophic Factor Release

This particular substance you may not have heard of.  It is released by the neurons in our brain, and helps new synapses to form.  How cool!  It is seen that in high intensity exercise, this substance increases the most.  It helps nerves to grow, improves neural synpases, make communication more efficient, and reduces neurodegeneration risk.  All in all, BDNF helps your brain to function more optimally.

Insulin Receptor Sensitivity

In order for insulin to be able to do its job, the receptors on our cells need to be sensitive to accept insulin.  When our receptors are sensitive and insulin can do its job, blood glucose levels become normal.  With too much glucose in our blood, we age more quickly and become more susceptible to inflammation, heart disease, and diabetes.  We also see an increase in energy, decrease in lipids, and a decrease in blood pressure.  With high intensity exercise we see this sensitivity for insulin go up, allowing insulin to do its job.  This response is also seen, but to a lesser degree with lower intensity exercise.

Immune Enhancement

With high intensity exercise, we see our immune systems functioning more optimally.  T cells are stimulated.  Growth hormone speeds healing.  Insulin receptors allow insulin to store blood glucose.  All of these helps with our ability to fight off infections.

Oxidative Stress & Risk for Overtraining Syndrome

With all the previous good, also comes the risk of increased oxidative stress.  This means an increase of free radicals.  Free radicals, once formed in the body, will go around scavenging healthy cells.  This will cause a decrease in healthy cell functioning and a decrease in energy production.  Excess of free radicals can also lead to cancer formation.  Along with an increase in free radicals production, it is also seen that with higher intensity exercise there is the possibility of a decrease in antioxidant production, which is what helps protect us against free radicals.  So it is important to understand this concept, to protect ourselves.  This is not a reason to not participate in high intensity exercise.  It is a caution to understand when you may be at risk for overtraining syndrome.  If one is at risk for overtraining syndrome, more rest and nutrients are needed for the body to recover and remove inflammatory cytokines.  I will address overtraining syndrome is a subsequent article.

Now that you know all of the benefits (and are aware of the risks), it’s time to get your but out there and get moving!  If you have trouble self-motivating, find a friend or find a trainer!  Both are probably readily available!  There are always people ready to help you with your fitness!  What do you have to lose?

My love,

Dr. Kristin



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