Running While Sick

By Kathleen Leninger, DPT

When you’re training, experiencing sudden post-nasal drip, fever, headache, or any other initial signs of illness can really throw a wrench in your plans. You have a hard decision to make; to run or not to run?  

Your immune system has a lot of jobs. It treats illness, attacks foreign bodies, keeps all of your vessels healthy, and repairs the damage done by illness or injury. When you are ill and fail to adjust your training, your immune system has to work overtime to try to heal both of these areas. Unfortunately, you do not make double the amount of immune cells, you’ll just have half the less cells fighting each battle. This will lead to impaired recovery from your activity.  

Research has also shown that a rapid increase in training can result in an increased risk of getting sick. If you aren’t increasing your recovery as you increase your training, your immune system has to work overtime to repair your muscles. As a result it isn’t able to fight off foreign bodies as well. Ever start to get a cold during peak week?  It’s not a coincidence.  

The following statements are some of the major research points featured in The Exercising Female: Science and Its Application

  • Prolonged activity (90 minutes or more) at 55-75% of your max aerobic capacity is the point at which your immune system starts to function sub-optimally.

  • Exercise causes a decrease in neutrophil and lymphocyte (most common white blood cell) function.

  • Cell cytotoxic activity (cleaning up the bad stuff) spikes immediately after exercise and then falls for 6 hours post-activity.

  • In women, estrogen actually binds to lymphocytes (white blood cells, which increases immunity! HOWEVER, increased amounts of cortisol (stress hormone) can damage estrogen cells and kill the lymphocytes, drastically weakening the immune system.

So what’s the take home message?  This is just one more chapter in the novel “All of your systems are relevant when running.” Don’t ever pretend your cold or fever isn’t going to affect your training; it’s all related. Use caution and don’t be afraid to rest when you’re not feeling well. Your body will thank you. 

Allgrove, J. And Davison, G.  ‘Chapter 10:Immune function and the exercising female’. The Exercising Female:Science and Its Application.  Forsyth, J. And Roberts, C. New York, NY: Routledge, 2019 125-141.