Neurotransmitters and Prolonged Exercise

Written by: Kevin Cann

            We live in an age where sleep is a luxury, chemicals fill our air, and processed foods make up the majority of our supermarkets.  To attempt to stay healthy and de-stress, we may go for a run, or sign up for a membership at our local gym. The lack of sleep and poor food choices may have made us get a little soft around the midsection, and instead of fixing those issues a lot of us decide we need to workout harder or run longer.  What we fail to understand is that this could be devastating to our physical and emotional health.

When we decide to make these decisions, we are wreaking havoc on our biochemical balance in our brains.  Serotonin and dopamine are two neurotransmitters that are responsible for our mood and energy.  We need enough of them floating around to elicit a response, and they also must be in balance with one another for us to feel good.  With our current lifestyles and living conditions, we compromise this balance, and this compromises our emotional and physical health.

Poor diet, lack of sunlight, stress, and caffeine consumption can all affect the abundance of these neurotransmitters.  What a lot of people do not know is that prolonged exercise also affects these neurotransmitters.  Studies showed that exercise caused an increase of serotonin precursors, as well as dopamine, in the brainstem and the hypothalamus.  These researchers stated that it is possible that the changes in the neurotransmitters could affect both physical and mental fatigue as well as mood (Blomstrand, 1989).

The central fatigue hypothesis was a theory developed to explain the fatigue associated with prolonged exercise.  Originally it stated that fatigue was associated with increased amounts of serotonin in the brain.  That hypothesis has now been changed to state that it is related to increased amounts of serotonin in the brain in relation to dopamine (Meeuessen, 2006).  These studies are important to understand for a couple of reasons.

For one, if we have decreased amounts of dopamine, or there is not the proper balance between serotonin and dopamine, exercise will be a difficult task.  We will fatigue quickly and it will not be a pleasant experience.  Also, if we decide to keep increasing exercise due to failure to reach goals, we can eventually burnout our ability to make these neurotransmitters, leaving us deficient in them.  This is where negative mood changes can occur.

Another issue comes in terms of our hunger response.  An increase in physical activity will drive us to increase our caloric intake to balance off the energy lost.  Kenneth Blum developed the Reward Deficiency Syndrome for addiction, and stated that he believes that glucose cravings and obesity are due to a lack of dopamine receptors in the brain (  Not only may our moods and energy levels be affected, but an increase in food cravings can occur as well.

Exercise that fits our lifestyles is an important factor to overall health.  If we lack sleep, are stressed, vitamin D deficient, etc. it may be a good idea to not exercise too strenuously. Also, we need to manage our stress, get some sleep, and eat a diet rich in amino acids and nutrients to give us the tools to build our feel good neurotransmitters.  There are times when we need some extra support to get through stressful situations and finding the appropriate healthcare practitioner can help.



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  1. says

    I agree, Kevin. The hardest thing is to know when to back off from exercise because too much of a good thing is starting to impact general health. This is why I stopped training Brazilian Jiu Jitsu *tear wells up in eye*. But replacing that chronic cardio 5x/week with 1x/week sprints and “intuitive” weight training sessions…my mood and libido and everything else is just so much better.

  2. says

    1) What is “prolonged exercise?”
    2) What is “exercise that fits our lifecycle”
    3) You say, “Fatigue associated with prolonged exercise is due to increased amounts of serontonin in relation to dopamine.” (Did dopamine decrease, or was there a surfeit of serontonin? Did both decrease, just not as much serantonin as dopamine?) If we increase exercie (even though it is difficult and we are fatigued) we will be unable to make these neurotransmitters at all. This leads to obesity and increased glucose cravings due to–
    4)”An increase in physical activity will drive us to increase our caloric intake to balance off the energy lost.” But this is part of the homeostasis sytem which, I thought, was “broken” in obese people (or how did they get fat in the first place?)

    Interesting article, but kind of confusing.

    • kevin cann says

      To answer the first couple questions, it all depends on the individual. Question 3, the evidence suggests that there is an increase in serotonin around the neuron itself and when this outweighs the increase in dopamine we get fatigued. Dopamine and serotonin need to be in balance. Question 4, physical activity increases our need to eat and replenish lost energy. This is a mechanism that has allowed us to survive as a species. If we are dopamine defficient and burn off enough energy to spike hunger we can get sugar cravings from two fronts (lack of dopamine and due to lost energy) and it will make it very hard to resist. Hope this helps!

  3. Zach says

    Good questions^
    I have another: if serotonin is increased in relation to dopamine would taking a drug that increases dopamine also decrease your feelings of fatigue? If so, what implications does this have for sport? A new drug program?

    • says

      I think that if we could find a way to keep serotonin and dopamine balanced during sport and glycogen stores full we could seriously delay fatigue. The problem is in figuring out current neurotransmitter levels and proper dosage.

  4. Sienna (also in Canada) says

    Good points and questions Alana. I agree w/ you. I wonder too what prolonged exercise means exactly. I mean most of the day I’m in front of my computer, sitting in my car or otherwise pretty sedentary. It makes sense to me to exercise every day, whether it’s a martial art, Bikram yoga, a strength training class or what ever.

    • says

      A definition of prolonged exdercise is completely individualized. Your current lifestyle and training experiencen will dictate it. Listen to your body. If you are having trouble recovering from workouts, not excited about working out, don’t feel good after a workout, then back it off a little. Pay attention to performance gains as well. If they start to dwindle, or you start to move backwards then you need to back off the exercise.

  5. Rella says

    As I read it, exercise is neurotransmitters depleting when it is 1) difficult to engage in 2) unpleasant and tiring 3) does not produce gains 4) leads to bad moods. The amount will be different for each individual.

    Having messed up my own serotonin and dopamine balance by years of unhealthy living, I think I am finally recovering because there are days when I look forward to exercise. And I am charting small strength gains in the gym. I just wish there was better understanding on how to rebuild neurotransmitter function after it has been trashed.

  6. Ann Marie says

    Love this article! I’ve been running into problems with mood swings and energy crashes after crossfit. Lifestyle is soooo important to take into account. As a full time graduate student, I have some weeks where I get much less sleep than others. I was also bartending for over 6 months where some days I would wake up at 7 or 8 am (after going to sleep at 3 am some nights), and other days I wouldn’t wake up until 12 or 1. I always struggled with trying to figure out when
    I should listen to my body and when I could “tough it out” and get a work out in. I love the social aspect of crossfit and hated to miss it when I could go but felt too tired. Sometimes I would feel better afterwards, but other times I would push myself too far and wind up crashing very soon after or having a HUGE emotional response. As soon as I stopped bartending I was able to go more times a week. However, I still run into days where I haven’t completely recovered from lack of sleep or soreness and low energy from an abnormally hard work out the day before. Those times I’ve literally come to tears mid or post work out! I guess that’s the nature of the beast though. Some weeks I can only make it once or twice, and others I’ll go four with no problem.

  7. Martin says

    The problem with prolonged exercise is that we use it to compensate for the lack of natural ‘movement’.

    Here is an extreme example: I used to work from a home office for a year, spending ~12 hours a day in front of my computer and I naturally lacked movement. To compensate for it I would run every day for 60-90min, then do yoga/gymnastics/stretch for another hour and would go climbing for another 2 hours every other. I needed that much to stay barely in shape (I hardly walked beside that!) and it seemed to work in the beginning but in the end I got seriously burned out, gained weight and my performance in all relevant areas went seriously down.

    Now, five years later, I move a lot, walking, cycling (relaxed, not pushing hard), etc. and I do not need long workouts. I still do a long run (in the woods, meditation-style) once a week, climb twice a week and do sprints and gymnatics once a week. I am in the best shape of my life.

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