Is Cycling or Running More Likely to Lead to Colds in Triathletes?


I train in swimming, cycling, and running multiple times a week.  While I am not as fast or efficient as I want to be in any of these three disciplines, I always feel the most drained after a hard run. Based upon this experience (an “n of 1”, so to speak), I would predict that intense running would make the typical triathlete more vulnerable to colds.  But, what is the evidence?

A recent abstract addresses this question.  My previous post in this blog explained that the level of the antibody, IgA, is affected by intense exercise and that people with lower levels of this antibody are predisposed to get colds (upper respiratory tract infections or URTIs).  In this study, eight male high-level triathletes (average age: 32.8 and average VO2 max: 72.6 ml/kg/min) performed a two hour bout of exercise at 55% of peak power output on both a cycle ergometer and a treadmill, separated by seven days.  Saliva samples were obtained pre- and post- both protocols to measure IgA (salivary IgA or sIgA).  Rates of secretion of sIgA and flow of saliva were also calculated for sIgA based on volume of saliva and time taken to produce a set volume.  Here were the findings (units were omitted for clarity):

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sIgA pre sIgA post IgA secretion rate pre IgA secretion rate post saliva flow pre saliva flow post
Treadmill 595 841 (*) 396 223 (*) 658 289 (*)
Cycle Ergometer 594 779 284 216 487 320
(*) statistically significant change

The authors state that “previous studies have shown that with a decrease in sIgA secretion rate and saliva flow rate there is subsequently going to be an increase in URTI episodes [e.g. colds] in the individual. This increase in URTIs can hamper an athlete’s preparation for competition resulting in sub-par performance, which may result in loss of sponsorship deals or contracts.”  They conclude that “the results suggest that long duration running may be more detrimental to immune function than long duration cycling in triathletes.”

These interesting results must be viewed with caution.  First of all, this report is an abstract, not a peer-reviewed journal article.  This means that the methods and conclusions were not carefully critiqued by experts in the subject, and, also, since abstracts are brief reports, we, the readers, cannot see all the details of the study.  Another area of caution has to do with this study possibly being underpowered.  This means that the sample size (8) may not have been large enough to capture true differences or to filter out “outliers” that can significantly alter results.  For example, suppose that, in the treadmill test, seven of the volunteers showed very similar results to their efforts with the cycle ergometer, but the remaining volunteer had a very high initial flow of saliva.  This would affect the average, but is is really representative of the average person?  Since this is an abstract, we cannot see the individual numbers to decide for ourselves.  Also, please note that the statistically significant changes in secretion of IgA and saliva flow in treadmill participants were related to their very high initial rates and that their post-exercise values were very similar to the participants in cycle ergometry.  Finally, the treadmill participants had statistically significant rises in total sIgA, not falls in sIgA.  Therefore, I am not sure if running is a bigger drain on the immune system than cycling.  For triathletes, we have to train in all three disciplines, anyway.  The practical application of this study to you may, possibly, be to choose cycling over running, if you have a choice, in peak periods of training, if you feel you may be particularly vulnerable to illness, such as after air travel.


The effect of exercise mode on salivary IgA secretion in high level triathletes. Barrett, S, Storey, A, and Harrison, M.  J Sci Cycling. Vol. 3(2), 3


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