Endurance Training & the Immune System


Experience From - Shelli Johnson, Karl King, Lynn Newton, Anders, Scott Sullivan, Jennifer Aviles, Dr. Bill Misner, Ph.D.,

Shelli Johnson

Although I haven't increased my weekly mileage by more than 10-15% at a time, I suddenly came down with the flu and bronchitis last Sunday, a day following a 16-mile training run. (my longest for this year)

I know the flu and bronchitis spread like wildlife, especially during this time of year.

But recently a physical therapist friend told me that distance athletes (athletes who put a relatively large amount of time per week into training) are more susceptible to infection. . .that distance athletes often walk a fine line between being 100% healthy and being sick.

Is this true?And, just how does training affect one's immune system? It seems like such a contradiction that one who trains hard and is in good physical condition is more susceptible to infections such as flu, colds, bronchitis, etc.

If anyone can shed some light on this for me, I'd be grateful.

Karl King

Well, this is a subject that has gotten a lot of study. Let me see if I can simplify the biochemistry for a short note instead of a dissertation. The immune system requires protein to function properly. When you run a short run, you burn very little protein, and get very little immune system suppression. When you run long enough to take down your glycogen supply, the body starts burning some amino acids (building blocks of protein ). That robs your immune system of needed materials. Immune system function declines until the amino acids in the body are back to normal.

The major focus of studies has been the use of branched chain amino acids, and the amino acid glutamine, as they are tied into immune system function.

Blood levels of these amino acids can be depressed for a day or two after a long run. That is enough time for your immune system to let you down, resulting in illness.

How to avoid this situation? Be sure to NOT skimp on protein in your diet. Take in protein or amino acids *during* your long run, and take in protein after your long run. When you take in protein, be sure to get some carbohydrate along with it so that the protein is effectively utilized.

In summary, suppression of the immune system following endurance exercise is real, and the way to avoid it is to replace amino acids during and after the endurance exercise.

Lynn Newton

Shelli wrote:

"... recently a physical therapist friend told me that distance athletes (athletes who put a relatively large amount of time per week into training) are more susceptible to infection. "
I don't have any answer to your questions, but am posting merely to second the query, because I've had a similar experience.

The first of this year I started ramping up with multiple long runs, and have been successful with that, i.e., I haven't suffered from injury, excessive soreness, or any of the maladies one might expect.

Then twice in three weeks I came down with cold/flu or whatever it was, bad enough to miss work. The first time was January 24-26, when I was home from work Tue-Thu following a particularly hard weekend on the trails.

Then last week on Thursday night I got whopped again, missed work Friday, and didn't run at all over the weekend. (I did get in some walking.) The weekend before I hit an all-time high in mileage for the weekend, and felt fabulous afterward.

Normally I don't get these bugs very often. Both my wife and daughter also came down *twice* before me. It's been like we've all been taking turns. So I assumed that it was just a case of catching the current thing going around. At the same time, I have to wonder to what degree running as hard as I have may have increased my susceptibility to catching the grunge.

Documented analysis on this would be interesting to read, if anyone knows of any.


It seems to me, ultra-novice that I am, that when increasing the load on the system (body, and therefore the immune) via increased training (read mileage, for most) that it is imperative to boost the amounts of things like vitamin C, E, Zinc, (etc. ...).

As the load on the system increases, the requirements to fight off cold, virus's, and alike, also increases. Where as before the increase, the body has an equilibrium regards the training volume (read load) and the requirements of the immune system to fight off the bad guys, the increase of training requires a boost of the items that support the immune system.

To wit: If I have been training 20 miles a week, with no ill effects on the immune system, and I increase the mileage to 40 miles a week, I can expect that my immune system may require additional help to ward off what I would normally be able to handle with no help.

Bottom line, the more I train, the more I feel I have to eat the right things, follow good training guide lines (rest on rest days), and supplement my diet.

Scott Sullivan

A couple of years ago, I seemed to always get sick after 50 mile races. I sometimes also got sick after hard training weekends. I started taking vitamins (which I never took before), and I have barely gotten sick since. I take a one general mineral pill, 500mg C, 400IU E, 100mg B complex, and 1000mg A. I think these vitamins really help me stay well.

Jennifer Aviles

My husband, Enrique, developed a formula a few years ago that he titled " Larson's Law. [don't ask me why that name; I haven't a clue.] that involves something he calls Larson's constant. The concept goes something like this:

the number of miles you run plus the number of hours you work raised to a stress factor is a constant called Larson's constant. The formula is: (hrsworked + mi run)**stress = K_larson. As you get older, your constant decreases. If you train consistently and healthily, your constant can increase.

So, for example, Enrique has figured out that his constant at age 43 is 80 based on the fact that if he works 60 hours a week with a stress factor of 1, he can run 20 miles that week (if he pushes himself) without either getting sick or "breaking (stress fracture, e.g.." Incidentally, this is tied into the thread just brought up re staying well and running ultras. If suddenly his stress factor went to .5 (highly unlikely), he could run farther.

When I was younger (eight years ago)I used to be able to run 40-50 miles a week and work 40 hours a week and still have energy left over. My constant was 90. This past 7 months I've been working 40 hours a week and running 10-15 miles a week and my stress points (father's terminal illness and recent death, new home, new job) have been off the scale plus I caught what we are calling here in Tucson the 4-5 week virus. Normally I catch a cold once a year at most. Don't you love diversity, though? We're all different in this respect and I often think we need to remember this individuality rather than try to adapt our bodies to follow someone else's training program without the necessary tweaks to recognize our individuality.

Dr. Bill Misner, Ph.D.

Chuck Zeugner's Search Query:

"Question 5. Do you know of any references or texts suitable for someone who has a good grasp of the physiology involved but does not have a medical education? "
Some of my favorite search-websites are here listed to assist you re: specific research-reference queries:




NEURON(Very Specific)










***Signifies RESEARCH studies which may provide you with specific answers to your questions from either abstracts or full copy texts.