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Susan Ivy
Susan Ivy, Nurse (RN)
Category: Health
Satisfied Customers: 4058
Experience:  BSN, MSN, CNS
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Recently after a very difficult 12 mile hike, with not other

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Recently after a very difficult 12 mile hike, with not other symptoms but tired knees and fatique, I had a sudden shaking chill lasting about 30 minutes. I am a very fit and active 65 year old woman.
Hello and thank you for using JustAnswer health for your question.

This is actually a commonly reported occurrence most often by marathon runners and athletes. They will often report having "flu symptoms" after an extremely intense work out. It has been found that certain immunomodulating proteins, called cytokines, are released during exercise, and some of these are "pyrogenic" (cause temperature elevation). There are also several studies showing a decrease in certain functions of the immunity, especially in the short period after intense exercise. So it is possible that your body was actually fighting off an infection or "bug" that you caught (the temperature elevates as one experiences chills, again, a sign of the immune system 'reveing' into action.) Getting less than optimal fluids and electrolytes during exercise can contribute to becoming hyperthermic (over heated) and this can also result in intense chilling as the body adjust to the temperature elevation.

Make sure you are continuing to drink adequate fluid, as there can also be some muscle destruction and these cellular breakdown products will be eliminated from the kidneys easier if you have adequate fluid intake.

It is also recommended to approach exercise cautiously, starting out gradually, and building to longer more intense periods of exercise over a period of weeks or months.

If you have further questions or comments about this please reply to this post so that I may assist you further.
Customer: replied 7 years ago.
I was not overheated nor febrile. The intense shaking chill ocurred about an hour after the hike ended. I had no "flu symptoms". AND when it was over, it was over.
In most cases there is a momentary spike of temperature when there are chills, even though not realized; that is the physiology behind chills.

But perhaps you did not have chills. If you had tremors or shakes this could have been due to an electrolyte imbalance, especially if it resolved after drinking or eating, and an electrolyte imbalance does not always occur with overheating, it can occur simply from exercising.

And, though it was not clear in the way that I stated it, I see when I re-read, it is still known for individuals to have the symptoms you described after exercising - some describe it as "flu like" because there can be intense shaking with chills, but that does not mean that they actually have the flu or have other symptoms of the flu. There are several kinds of cytokines.

If you are concerned by all means see your physician so that a physical can be completed. It seemed by your report that you were no longer having symptoms, (you mention that again in the next reply) so that is why I did not originally mention evaluation.
Customer: replied 7 years ago.

I have not made myself clear or given enough information. This event was two days ago. I am fine now and was fine thirty minutes later. It was an actual chill.....I was freezing cold and shivering in spite of blankets.....though no fever or other symptoms. It was very sudden, about an hour after extreme exertion. I have no symptoms now. I am simply interested in figuring out why this happened.....and, of course, preventing any future episode.


I did understand you, and am not sure why you do not understand my reply, except that probably too many details that do not make sense if you do not have a background in biology and human physiology were added. I apologize for any confusion. What is important for you to understand is that, chilling such as you describe can occur after an intense period of exercise. It is a physiological response of the body resulting from a type of protein that is released into the blood stream during intense prolonged exercise of which the body is not accustomed.

To prevent it from occurring again, it is recommended that you do not take a hike of this length.

If you are interested in further hikes of this nature, it is recommended that you gradually build up your physical tolerance, over a period of months; or spread the hike out over several days.

As a health care provider it is of my nature to teach prevention, so I remind you, in case you are not aware, that it is also recommended, for everyone, to see their physician before starting a new exercise regimen or a higher level of physical activity. Another action that can benefit those that are planning on increasing their level of activity is to hire a certified fitness trainer (with doctor's approval). Some fitness trainers will work with a group of individuals at the same time, not only to make it more cost effective for the participants but also because some people enjoy the social interaction. If you are a member of a gym or fitness center, you may be able to obtain these types of services at no additional cost.

Customer: replied 7 years ago.
Hmm....Well, not too surprising that you would not exactly know how to advise someone "outside the box". I said I was a very fit 65 year old woman...participating in hi-lo and or step aerobics four to five days a week for almost 26 years and doing lots of recreational hiking, including a hiking vacation in the Italian Alps. Also, I have regular physicals and a degree in Biology. This was not my first 12 mile hike. Just the first time to experience a shaking chill afterward. That's why I was curious!!

Being a backpacker and hiker myself, I know very well that 12 miles is a lot at any age!. But besides that, it was you your self that said it was a more difficult hike than usual. Also, you indicated that you did not understand what I was talking about, and this information is related to the immune system mechanics, and since I took physiology myself there has been a lot more discovered about how it works - so any one not reading this information and keeping up with it yearly might not understand all the details about how it works. So there should be no offense taken at any thing I have said. I will opt out though of your question and this will allow another expert to take a shot at it. It has been nice working on your topic, and I hope you continue to enjoy your active and healthy life!

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