“Why Do I Get Sick From Intense Exercise?”

February 6, 2008 – 3:40 pm

Some students following TACFIT® programs designed for my first-responders and fighters have been contacted me about a strange phenomenon, despite their amazing physical improvement. Some have experienced flu-like symptoms about 2 weeks into the initial phase of metabolic conditioning. It’s not unusual, and I thought I should take some time out of my schedule to explain one of the theories why this happens.

Firstly, get everything checked by your physician. That caveat aside, there is a phenomenon known as the Jarisch-Herxheimer Reaction (and sometimes just as “Herx”), which happens when the body tries to eliminate toxins at a faster rate than they can be properly disposed of.

High intensity conditioning can act like a furnace to bacteria, and when that bacteria dies, it can release large quantities of toxins into your bloodstream. Metabolic conditioning can release toxic stress chemicals stored in your fatty tissues at the same time. This places a toxic burden on your immune system temporarily, which is why powering up nutrition before metcon days and doubling your hydration after sessions – especially for the first few weeks – is critical!

The more toxic your system becomes, and the more severe your metabolic conditioning, the greater this event becomes, often referred to as a “healing crisis.” When the bodily systems start trying to process this sudden dump of sewage into your system it starts working feverishly to eliminate waste products through any and all elimination channels so it can start to set the stage for regeneration back to normal levels.

When an intense physical exercise program causes a large scale slaughter of bacteria, huge amounts of endotoxins (stored within the bacteria) release into your bloodstream. The more bacteria stored in your tissues – and the more intense the session, the stronger their endotoxins, producing even more stronger symptoms in the body to try and process out all the junk. When an intense physical training program (or for that matter, even fasting and detox treatments) causes your organs (such as the liver – your poison warehouse) to discharge their stored poisons, then these crisis symptoms can happen.

When you have a balls-out kick-ass session which causes fast breakdown of fatty tissue (another toxic warehouse), you can experience these symptoms as your body works to process out all of the toxicity. You often experience it as this temporary increase in symptoms in the first few weeks of turning up the juice in your metcons.

About 2-4 days after a very severe session you may feel horrible, like you’re coming down with the flue. But these symptoms are part of your body processing out toxic burden, impurities and imbalances.

You may feel horrible for a couple days, but on rare occasions you can feel sluggish for a couple weeks. You’ll feel fantastic from your session, and then hours later, just suddenly start to have a host of symptoms like headaches, joint aches, nausea, ear ringing, etc. A lot of fighters unused to this intensity of exercise will feel a little ill during the first few days because it’s then that your body “dumps” the toxins back into the blood stream for elimination.

In more serious situations, you may go through small crises like this for a longer duration, cleansing out the toxicity and restoring the purification process of stored waste by-products from high intensity exercise back into a free flowing state. For these more serious conditions, I strongly suggest working with an endocrinologist and/or naturopathic physician.

There are a wide variety of reactions that may manifest during a healing crisis, the most common are:

  • Arthritis
  • Joint Ache
  • Cramping
  • Diarrhea
  • Headache
  • Nausea
  • Congestion
  • Fever
  • Chills
  • Rashes
  • Hives
  • Fatigue
  • Restlessness
  • Insomnia
  • Moodiness
  • Rage
  • Anxiety

Hydrate in advance of a session and double your hydration afterward. To stay adequately hydrated, multiply your bodyweight in pounds by 0.55-that’s about how much water you should drink in ounces everyday. For example, a 200 lb. person needs about 110 ounces of water daily. This is about 10 to 12 glasses of water depending on the size of the glass. Juice and herbal tea also help you flush out these toxins.

In addition the following will help expedite your elimination of the toxicity: sleep, bowel movements / enemas, acupuncture, massage, steam baths, dry saunas, whirlpools, lots of green veggies, naps, skip your next metcon session.

A final restatement of my first suggestion: see your doctor for a check up. It could be something worse. This isn’t medical advice. I’m not your medical doctor. What you’re experiencing may not be the above. It could be something that was dormant or not above the radar of your attention until you trained intensely. You may have a severe health issue. Be safe by being certain.


  1. 10 Responses to ““Why Do I Get Sick From Intense Exercise?””

  2. i just wanted to let you know that your website is awesome information. i recently started working out at the gym. when i would get done, i would have hives that itch and they would stay for about 30 minutes or so. i didnt understand why this was happening. then if i would clean around the house, id get hives. anytime i worked up a sweat i got hives. when i read your information, it seems to be exactly what is going on with me. i am going to get a doctors oppinion if it continues, however for now, i am at ease…thank you so much.

    By jen on Mar 24, 2009

  3. Since I can remember up until age 37 I’ve always been in shape. I never understood why people struggled with push ups or pull ups, I was never big, but definitely strong for my body size. At age 38 some aspects of my lifestyle started changing, mostly b/c of stress. I recently turned 40 and decided to get back in shape, every time I start a work out I come down with a bad cold/flu like symptoms lasting about 1 week, then I start again only to fall in the same problem. Doctor clears me as healthy, suggests I loose some weight (no kidding). Your website gave me some awesome information and I now know to look in another direction. Thank you for your information.

    By John on Mar 4, 2010

  4. THANK YOU! Hits the nail on the head for me. I felt better as soon as I read the article, knowing that 1) this meant toxins were being release from my body 2) I was buring fat during my workouts (spin followed by weight training) even though the scale hasn’t moved yet.

    By Jamie Lynn on Feb 21, 2011

  5. I googled this topic and read your article. Explained my situation exactly. Is there hope for the arthritis part? Will the intensity of symptoms pass or is it likely that if it’s still present 8 months later it’s here to stay. I have been taking a rx for this and would like to go off it, but have not been successful d/t continued bi-lat knee pain. Zumba 2 x a week and am active and busy the rest of the week with day to day things.

    By christa webb on Apr 6, 2012

  6. This is the most helpful article I have read on this subject and it is exactly what I am experiencing. For my whole adult life I have worked out intensely for 5 days a week minimum. I recently had my first child and my workouts are few and far between. When I do find the time I work out the way I used to and it just trashes my body. Almost exactly 36-48 hrs after my workout I get severe chills, sweats, and body aches. These symptoms go away within a day or two but are uncomfortable to put it lightly. Thanks for the insight, I am sure this article will help many people.

    By Jeff Baldino on Jun 18, 2012

  7. This is the article that keeps on giving! I too agree with all the other commenters. This is by far the most informative and educational article on the web relating to feeling I’ll after high intensity met-cons.
    I ate some steamed spinach and am now on my 3rd 8 oz glass of water. Feeling better already. Thank you, Thank you!!! :)

    By Andrea on Nov 26, 2012

  8. I am currently home from work sick because I have had a fever for 2 days, nausea and vomiting. I am a 51 year old female who has never been an avid exerciser but I keep trying! About 2 weeks ago I started walking daily on the treadmill in work on my breaks,15 minutes twice a day. Not a huge amount of time and hardly a killer workout but I was moving. Last week I pushed the level up and changed the intensity level slightly. This week I am so sick I can hardly stand without getting dizzy or nauseous.My doctor can not find anything wrong and calls it a virus. This happens every time I start an exercise program. I get into it then get sick and am off course again for what could be weeks until I feel totally better. How do I prevent it or make it easier to handle? I mentioned this to my doctor and she had no idea what I was even talking about and looked at me like I was crazy. I am so glad to find your article so I see I am not the only one that equates working out with getting sick!

    By Kathy on Jun 18, 2013

  9. Kathy, go to a naturopath and get a blood exam: thyroid, adrenal, iron and blood sugar levels.

    By Scott Sonnon on Jun 18, 2013

  10. Thank you for this article, Im a 21 y/o male lean 6′0 170-180 pd Firefighter/Emt in Florida and im experiencing this- I train 4 days a week, usually every other day, I begin a training routine slow and steady working my way up but after about 3-5 weeks at about the 5th week my intensity during my workout has increased drastically from the first week. After lets say a heavy leg day I begin to feel tired and exhausted, 2 days later I have a cold… It is extremely frustrating because every time I get to my peak this happens to me… It gets in the way of my job, paramedic school, lifestyle. I love what I do and I have a passion for fitness as well but this has been a constant road block.. Any advice would be highly appreciated. Thank you very much

    By Bam R on Jul 9, 2013

  11. I am currently in bed recovering from headaches and quite bad nausea to the point where I haven’t eaten for 2 days. Just before this started I did 2.5 hrs of solid netball and am still so sore it hurts a lot to walk. Loved your article. I’m starting to feel better but hoping this doesn’t occur after grand final in 2 weeks time. Will do some cleansing and liver/ immune support over the next couple of weeks.

    By suzie on Aug 11, 2013

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