The physiology of stress

Do adaptations to stress exposure show up as changes in blood chemistry or heart function?  The answer appears to be “yes”.  In his Newsweek article “Lessons in Survival”, Ben Sherwood reported on a very interesting study of elite Army Airborne and Special Forces soldiers that probed the differences between those who could and could not endure an extremely stressful 19-day mock-prisoner-of-war camp.  The Resistance Training Laboratory, located at a secret location near Fort Bragg, North Carolina, subjected participants to sleep deprivation, blaring music, semi-starvation and — worst of all — intense interrogation techniques used by enemy forces during WWII, Korea and Vietnam.  “The goal is to simulate hell on earth like the Hanoi Hilton in Vietnam or Al Qaeda’s torture chambers,” according to Sherwood.  In another test of mettle, at the Navy Diving and Salvage Training Center in Florida, trainee divers were put through stressful routines such as being thrown into a pool with their hands and feet bound, and underwater ocean swimming from 3 miles offshore to a target on shore.

Biological markers. After these ordeals, Dr. Andy Morgan of Yale Medical School found that the top performers had very different physiological responses from those who couldn’t hack it. He did extensive physiological monitoring and found that those who passed these tough tests had much higher levels of NPY (a neuropeptide) and DHEA (a hormone that buffers the effects of cortisol, a stress hormone).  In addition, those who did best also had “metronomic heartbeats” — very little heart rate variability (HRV), compared to most normal people, who show a lot of variability in the intervals between heartbeats.

These biological markers of stress-resistant individuals show that they are somehow different than most of us.  Perhaps this is worth looking for what it can teach the rest of us.   Certainly, there are other health known health benefits that have been reported for NPY and DHEA.

Autonomic nervous system. Regarding HRV, however, Sherwood raises a caveat, noting that numerous studies have associated metronomic heartbeats (low HRV) with cardiovascular disease, diabetes, and even sudden death.  However, other research into the HRV paints a more complex picture.  A paper on the Intellewave Method,  by Dr. Alexander Riftine,  indicates that low HRV may have different implications for the state of the autonomic nervous system, depending on the frequency of the heartbeat variability, derived from heart rhythmograms.  When spectral analysis (a mathematical technique based upon Fourier Transforms) is applied to the heart rhythmograms, the heartbeat frequency variations are resolved into high frequency (HF) and low frequency (LF) patterns.  The LF variations are associated with the sympathetic nervous system (SNS), where as high frequency HF variation correlate with the parasympathetic nerous system (PSNS).  The balance between SNS and PSNS states predicts much about an individual’s fitness.  According to Dr. Riftine, these states cluster into nine typical combinations.  The ninth state–an elevated PSNS with a reduced SNS state–is “rather unusual because normally an increase in PSNS is accompanied by an increase in SNS.  This rare condition is found in water polo athletes, long-distance runners, navy seals and persons with special heart training for deep sea diving.”

The physiological analysis of individuals who have successfully adapted to tolerate stress is a promising area ripe with lessons for the rest of us, as it could be used to assess, predict, and track our progress in getting stronger and more stress-hardy.



  1. Wayne Martin

    I just looked at the Intellewave website. It makes the claim that it’s “the first and only such system available today”, and as a psychophysiologist myself, I have to point out that there are a number of systems which measure the HRV signal and provide feedback to clinician and subject.

    BTW, I find the information you provide on Hormesis to be quite refreshing. It offers some balance, IMO, to the standard party line I was trained in: Decrease Distress. Little was said about Eustress in my training other than acknowledging that Eustress exists.

    Thanks, Wayne

    • Todd


      Thanks for the information on HRV measurement. Do you use that routinely in your practice? I had thought it was a fairly sophisticated and expensive technique, but perhaps it would be useful for average Joes like me to get tested periodically, so that we understand our stress response capacity.


      • Wayne Martin


        Yes, HRV can be quite accessible. Clinical grade equipment is what a biofeedback therapist would have (find them at That equipment runs in the 3-5k range typically. There is some cheaper equipment that is based on the same concept and is in the $200-300 range (,

        It looks like you’re in the San Francisco area, and I know of a terrific psychophysiologists there you could see for an assessment if you wanted.

        If you like, contact me privately for some further discussions because I can share some relaxation recordings with you which may be helpful.


  2. Carmelite

    I am a single mother to a young son, and am also a student about to start my last year of nursing school. I live with my mother and sister, who are a huge help to me. My mother, however, can be a challenge to live with as well. She has a rare autoimmune condition (CIDP), as well as celiac’s, obesity, and depression. She needs a lot of help and is frequently extremely reactive emotionally. My family does not have very much money, and we are struggling to get by on various aid programs until I graduate. Despite the difficult circumstances, I am determined to take care of my health and manage my diet, exercise, and psychology as well as possible. I don’t want to end up like my mother. My question is this: how best to proceed when chronic stress is an unavoidable aspect of my life right now? Nursing school allows or almost no routines. Schedules shift day to day and week to week. Some nights I might get 2 hours of sleep and have to get up for clinical at 4:30am. His last semester, my diet and exercise routines completely fell apart. All of my energies went into sleeping, studying, and trying I be kind I my son. Now that I’m on winter break, I’m trying to restart some healthier habits. I was drawn to your site because if the emphasis on gaining strength, adaptability, and tolerance to stress. I have been taking cold showers for a week now, and am loving them. I want to start the deconditioning diet this week as well. I’m a little concerned about adding too much stress to my life, even intentional stress. Should I be concerned? Do I need to alter any of your recommendations to account for my baseline high stress levels (ie, should I not be doing IF when my life is frantic)? Do you have specific recommendations for how to handle chronic, unavoidable stress? Hopefully, after I graduate next year things should et easier. I will no longer be living below the poverty level, at least, ad hopefully my mother will be moving to live with my older brother, so I will have some help dealing with that stress source! Thank you!

    • Todd

      Hi Carmelite,

      I admire your efforts to rise above your circumstances. You are right to realize that trying to avoid stress is unrealistic. Gaining strength and resilience is the only sustainable solution. And it has a hidden benefit: not only does hormesis help you to resist and adapt to stress; it also builds a sense of pleasure, accomplishment and pride that serve as their own rewards!

      Your concerns about adding too much stress too quickly are very perceptive. This is the single biggest mistake that people make in trying to increase their resilience! It may seem paradoxical, but you’ll build strength more quickly if you approach it gradually. Just as training to run a race or compete athletically is best done gradually, the same applies to exercise and diet for health.

      If you want to try the Deconditioning Diet, do it in steps as I outlined in my Diet post. I think that a low carb diet with lots of protein and fat is a good place to start. Don’t skimp on the fat — it really speeds the adaptation and the weight loss — and keeps you feeling satisfied.

      The deconditioning part is probably best tried first when you have a calm week, and do it in small steps. Eventually you can try it during a normal, stressful week.

      Intermittent fasting is a very powerful way to get control over your eating and the stresses in life. But it is generally a bad idea to start out with long fasts. This often causes hunger headaches, light headedness, crankiness, and rebound eating. Start off very slowly by just eliminating snacks and eating 3 solid meals. After you have that down, you might consider delaying or skipping breakfast or lunch. The secret is to to this gradually.

      I’ve collected my suggestions and tricks for doing in this in my post “Learning to fast“.

      Another benefit to building your resistance gradually is that you’ll see yourself succeeding — and success breeds self-confidence.

      I also believe that you will benefit enormously by learning the psychological techniques of the Stoics. The best book on this is “A Guide to the Good Life: The Ancient Art of Stoic Joy” by William Irvine. After you read that book, I bet you’ll be smiling and even laughing at the stress from nursing school, lack of disposable income and your wonderful family — and wanting to take on even more challenges!

      Good luck to you, Carmelite. I think you have just what it takes to succeed!


      • Carmelite

        Thank you so much for the reply, Todd! I am definitely going to pick up that book. Reading is one of my greatest pleasures in life, so I’m planning on using it as a possible counter conditioning tool for cravings (I have skipped many a meal to finish a good book before:). I have continued with the cold showers and am loving them, and have been eating moderate carbs for about 10 days now (<200grams/day). I am also about to start a once weekly workout at a local gym with a trainer who specializes in HIT resistance training. I am feeling well on my way! I have a couple more questions for you regarding assimilating some of your reccomendations. One that I struggle with is scheduling meals. My days are so utterly lacking in routine, that I find the idea of keeping regular meals a bit daunting. Some days I start clinical at 6am and won't have a predictable break to eat 'til noon. Work days can start at 6:45am, school days at 7 or 8 or 9. When I'm at the hospital, things can get busy in random waves, so that I may break for lunch at 11am one day and not til 2 pm on another. My sleep schedule is also pretty erratic, which doesn't help. I'm a night owl by nature, but often have to get up early for school or work. I have a really hard time getting myself to go to sleep at a regular and reasonable hour each night, even when I know I will be working a hard, physical 12 hour shift the next day, and some nights I have to be up late to study. So, I guess I have two questions: 1) can I modify your diet reccomendations to not include regular meal times? Perhaps limit to three meals a day but plan very broad windows of time in which to have those meals? 2) do you have any advice on how to shape myself into going to bed on time when I need to (and when my schedule allows) that still allow for the odd nights when I need to stay up or choose to stay up later?

        Thank you so much! Your site has really struck a chord with me. I have intuited for a while now that resilience and adaptability are my goals, but had not realized others were out there collecting data on how it can be achieved!

        • Todd


          I don’t think I said anywhere in my article that meal times should be regular, did I? I’m like you: my pattern of eating is irregular. Some days it’s just dinner, other days lunch and dinner or breakfast and dinner, and occasionally all 3 meals! And the time of eating each meal can vary by hours. I agree with Art DeVany that eating should be “fractal” — a bit unpredictable and irregular. (Another book for your reading list:: The New Evolution Diet). It keeps your body guessing, rather than locked into a pattern of expectation. The result is that anticipatory appetite doesn’t build up, probably because ghrelin signaling is weakened.

          Some of the Paleo advocates think we should maintain very strict daily patterns in synch with “natural” circadian rhythms. I tend to think we humans are quite adaptable, within fairly wide limits. That’s not to say we have infinite flexibility. Certainly it is important to get adequate sleep. So unless you have a problem with insomnia and fatigue, I would not stress out too much about regular sleep times. The main advice is to get enough exercise and healthy stress that you sufficiently exhausted each night to fall asleep readily and sleep pleasurably.


          • Carmelite

            Thanks again, Todd! I think I was misunderstanding the part of our Deconditioning Diet where you advocate scheduling mealtimes. I assumed that meant you should schedule the same times each day. I just realized that you actually said to schedule the night before and then you can still change them as long as you plan to at least 30 minutes beforehand. That’s quite a bit easier to do:). I think, most likely, that scheduling the night before will nearly always be pointless for me. I’m thinking I’ll just aim to have my 2-3 meals most days, at least 3 hours apart and 3 hours before bedtime, and try to wait until the peak of hunger has passed to eat as often as possible. I’ve been inching my way in that direction this week already. I have been an all day snacker for awhile now. Today is my first day cutting out all snacks except my bedtime snack (that will be the hardest one for me to drop), and it is going well! I’m loving the gradualism of this approach.

            As far as sleep goes, I have no troubles with insomnia. When I turn my light out and lay my head down I am generally out within 10 minutes. My problem is with the will power needed to convince myself to stop reading my book and turn out the light by 9:30 pm so that I can wake up by 5:30 am. I generally feel pretty wide awake at 9:30, even if I’m sleep deprived and was exhausted the whole rest of the day. Basically I’m seeking a way to motivate myself to turn off the light and go to sleep so that I don’t end up more sleep deprived than I have to be. There are some days I will not have the choice to get enough sleep because of unavoidable scheduling issues, so I need to catch up when I can so as not to be chronically deprived.

            The problem is that that time in bed at the end of the day, reading a good book, is often my only time alone all day and it is often my favorite time as well. I frequently fail at convincing myself to keep it to a reasonable length:)


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