The cold and flu season are well underway and in Canada this year, hospitals are seeing higher volumes of patients with influenza (Dangerfield, 2017). Many of us who exercise regularly debate when a cold hits whether it is smart to “sweat it out” or stay home and get some rest instead.

Every day out bodies face germs, bacteria and viruses. The most common invaders are upper respiratory tract which include but are not limited to: colds, coughs, influenza, sinusitis and tonsillitis to name a few. Luckily when our immune system is faced with a foreign invader it works hard to defend us. Our immune cells originate in our bone marrow and thymus. They interact with invaders through the lymph nodes, the spleen, and mucus membranes. Which ultimately means they first make contact in your mouth, gut, lunges and urinary tract.

When trying to decide if you should consider exercising with a cold or the flu it’s important to understand the effect exercise has on the body. Exercising boosts the body’s metabolism, as well as the immune system. However, a vigorous workout can have the opposite effect. During exercise our body releases chemicals to repair itself and control the level of stress in our bodies (Gleeson, 2007). This is very helpful when fighting off infections. However, when levels of exercise get too intense a steroid, cortisol, is released by our body to fight off stress (Gleeson, 2007). Cortisol can decrease the ability of the cells that fight off infections to work and therefore lowers our immunity temporarily (Andrews, 2018).


A structured workout plan, one where you’re working hard, sweating and feeling some discomfort awakens a stress response in the body. When we’re healthy our bodies can easily adapt to stress. Over time this adaptation is what makes us stronger. But when we’re sick, the stress of a tough workout can be too much for our immune system to handle.

A study on mice tells us a good story about exercising when sick. Three sets of mice were given the flu virus. The first set were sedentary mice and this group caught the flu. The second set did 120mins of running on a treadmill. Unfortunately, they had the highest number of flu infections and deaths. The third group were previously active mice. They also caught the flu infection, but they recovered faster than the first set of mice. From this experiment, the conclusions were that exercise can expose you to germs, but you can recover faster and have fewer complications (Murphy, 2008).

There is still much research in the field of immunity and the role it plays in exercising. However, for now the following conclusions can be made:

  • Consistent training can strengthen the immune system. Train hard while you’re healthy!
  • A single high intensity or long duration training session can interfere with immune function when you have foreign invaders in the body.
  • You can’t “sweat out a cold”. Plain and simple, no matter how good you may feel after a sweaty workout there is no proven research that working out helps combat a cold. Instead, a temporary serotonin boost might account for your overall sense of feeling better (Gleeson, 2007).
  • If you are participating in high intensity exercise when you have a cold be sure to drink plenty amounts of fluids.

Listen to your body when you’re feeling under the weather and make the appropriate adjustments to your training when needed.

Author: Megan Cook


Andrews, R. (2018, January 11). All About Cortisol. Retrieved from Precision Nutrition:

Dangerfield, K. (2017, January 11). The flu season in Canada is getting pretty nasty; here is everything you need to know. Retrieved from Global News:

Gleeson, M. (2007). Immune function in sport and exercise. Applied Physiology, 693-699.

Murphy, E. (2008). Exercise stress increases susceptibility to influenza infection. Brain Behaviour Immunity, 1152-1155.