Sometimes when you come down with a cold or flu while training intensely, you know that pushing yourself too hard was the culprit. While it’s understood that excessive training can make you vulnerable to illness, the factors that make it more or less likely are not well understood. This month, the Journal of Strength and Conditioning Research released an in-depth study investigating the effects of exercise intensity on immune response.


Training intensity, exercise duration, lack of rest periods, or even how your training makes you feel may all make you more likely to get sick, but we just don’t know which of these is to blame. One way to figure it out is to study the body’s defenses to illnesses. In this study, the researchers measured an antibody called immunoglobulin A to gauge exercise’s effects on immunity.


Immunoglobulin A is primarily found in the mucosal linings of the body. It can also be found in our tears, saliva, and stomachs, and is hardy enough to survive in harsher environments than other immunoglobulins. Immunoglobulin A is produced in large quantities in the body every day. In fact, you probably produce more of it in a day than you consume potassium, the body's most abundant micronutrient.

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Here’s how immunoglobulin A works. As the first line of defense in preventing illnesses, immunoglobulin A is active at the places of your body where infections are most likely to take place. Anything that suppresses the immune system results in fewer antibodies, and thus a reduced defense. According to the researchers in this study, reduced immunoglobulin A can be a sign of an upcoming illness, and is detectable several weeks prior to it becoming symptomatic. Immunoglobulin A may be suppressed for weeks after an illness, as well. Once your immunoglobulin A levels drop below forty percent of normal levels, you have a fifty percent chance of contracting an upper respiratory infection within three weeks. In other words, this stuff is critically important.


In the Journal study, the researchers used a simple saliva test on a group of soccer players. The athletes either performed four high-intensity training sessions, which were characterized by greater distance and higher perceived exertion, or four low-intensity training sessions, which focused on technical drills. The researchers measured immunoglobulin A levels for a one-week period to determine immune response.


The researchers found that after the first three sessions of the week, the immune response was roughly the same for the low- and high-intensity groups. However, the high-intensity training resulted in a significantly suppressed immune response after the full week. This trend was observed immediately after the four sessions of intense training when compared to lower intensity sessions. Interestingly, the pre-training values were the same for high- and low-intensity sessions, meaning both groups of athletes recovered at the same rate.


Since more work and greater perceived intensity both lead to a greater suppression of the immune system, it is prudent for athletes and coaches to track their intensity and adjust if they start to notice symptoms of overtraining. You can also get a kit to test your actual immunoglobulin levels, but careful tracking might make this unnecessary.



1. Adam Owen, et. al., “High Intensity Training and Salivary Immunoglobulin-A Responses in Professional Top-Level Soccer Players: Effect of Training Intensity,” Journal of Strength and Conditioning Research, DOI: 10.1519/JSC.0000000000000380.


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