Exercise immunology sits right next to doping urine analyzer in a competition for most boring sport related jobs. That’s why even we have been surprised by our sudden interest in some recent research out of the immunology field as it pertains to your immune system and extreme exercise.

We have long cautioned athletes that while in general, exercise makes your immune system stronger over time, too much acute exercise (working out too hard in too short a period of time) leads to a short term weakened immune system and makes you more susceptible to attracting viruses and diseases during that ‘open window’.

Alex Hutchinson, a great Canadian sports sciences author, directed his readers to a few recent studies on this topic that caught our interest. The first, out of the United Kingdom, is a very thorough critical review of all research on the topic. The authors go into great detail to address what they call ‘the myth that exercise can minimize immune function’ and among other conclusions they state:

1. Exercise per se does not heighten the risk of opportunistic infections
2. Exercise can ENHANCE immune responses to bacterial, viral and other antigens
3. They also presented evidence showing regular physical activity and frequent exercise may limit or even delay immunological aging!

After reading this, it sounds to us like the advice we are doling out may be wrong.  They even suggest extreme exercise (ie running a marathon or crossfit) does not have reliable evidence to show a heightened risk of infections.

They do acknowledge that many people feel that they get sick after running a marathon, but they think any sickness is actually more likely to due with being around so many people and attending a mass participation event to begin with, and not the actual act of running the race.

Now you can never hang your hat on just one paper.  Hutchinson even points out some data showing 120 minutes of low intensity running reduces immune sensitivity vs 30 minutes, even if the 30 minutes was at greater intensity, suggesting prolonged exercise may be tougher on us.

The author of this research, Neil Walsh, recently published a large review almost as a sort of rebuttal to the prior mentioned review which still had heavy exercise as a risk factor in lowered immunity.

But, the same review also points out that elite distance runners actually get sick LESS OFTEN then non-elite runners.  It turns out there may be genetic and/or modifiable behavioural factors accounting for why these top level athletes get sick less such as better sleep, stress management and hygiene, as well as the fact that these athletes typically do not have the stresses of actual work on top of their athletics. So in general, they are ‘healthier’ and get sick less.  Something any of us can follow.

So then where does that leave us? We feel that our prior opinion that heavy exercise leaves you with a ‘window’ of susceptibility for infection is now shown to be a bit heavy handed. Maybe the fact that you got sick after your marathon has more to do with the stress of training for the race, and being around 15,000 people then with an acute decrease in your immune response. Food for thought anyways. The Walsh review provided  7 practical recommendations to decrease your chances of getting sick with training, which are pretty good.  Probably more important is OUR recommendation that if you stay healthy, sleep lots, and eat well, then you probably have nothing to worry about after a heavy bout of exercise. Happy (and healthy) training:

1. Manipulate training volume and/or intensity to manage training load
2. Keep the size of increments in volume and intensity to 5-10% per week; particularly important during winter
3. Increase the frequency of shorter, spike training sessions rather than enduring fewer but longer sessions
4. Implement recovery activities immediately after the most intensive training session
5. Undertake easy-moderate training sessions after each high-intensity session
6. Plan an easier recovery/adaptation week every second or third week of the training cycle
7. Permit athletes at heightened risk of illness several weeks of active recovery after completion of a season or major competition.