We've all weighed the costs and benefits of working out when sick: "My throat hurts, so I'll stick to weights and avoid heavy breathing." Or, "maybe a good sweat will break this fever." Often times, it just boils down to, "yeah I feel like crap, but I have a plan I have to stick to." So we compromise and try to push through our workouts, even though we’re suffering (more than normal, that is). After all, what doesn't kill you makes you stronger, right? Well, while forcing a workout when you’re under the weather probably won’t kill you, it's also not necessarily making you stronger. Here's why.
How exercise affects inflammation and your immune system
First, let’s go over how your immune system relates to training and recovery: Exercise puts different types of stress on our bodies, typically physical. Take weight training for example; when you perform heavy squats, you exert physical stress on your muscles, which damages them at the cellular level. Your body then mounts an inflammatory response, which routes oxygen, nutrients, and immune cells to your muscles to kick off the repair process. It's this process that can cause elevated levels of hsCRP, a biomarker for total body inflammation, and creatine kinase, an indicator of muscle breakdown, after an especially tough workout.
In addition to mobilizing immune cells to our muscles, exercise has also been shown to affect our overall levels of white blood cells (WBC). In fact, certain types of interval training increase WBC in the body, and moderate-to-intense training can help optimize types of WBC known to fight viral and bacterial infections.1,2 So don't be too alarmed if you see increases in this biomarker after a change in your training routine. Think of it as immune system training; it's through this mechanism that exercise can help build a strong immune system. In fact, there’s evidence that those who exercise regularly have lower chances of catching the common cold than those who don't.3
Is it ok to train when I’m feeling sick?
Well, now you know that exercise can induce elevated inflammation levels and, in turn, WBC numbers. But, if we’re sick on top of this, our bodies might not be able to respond to both exercise-induced inflammation and that caused by a sickness. Therefore, our ability to mount a proper immune response to fight off infections is severely inhibited. Of course, we know it can be hard for some people to weigh a day of training with a day in bed. So, by following some simple guidelines about training when sick, you can still get in your workout and get rid of the runny nose at the same time.
When it’s ok
Generally, if you’re experiencing symptoms that are “above the neck”, it is ok to take part in mild exercise. These include symptoms such as a light cold, runny nose, sneezing, and a minor sore throat. In my experience, a light training day can actually help open nasal passages and clear out congestion – but do take some modifications into consideration:
- Reduce training intensity and duration. Long and intense workouts can suppress the immune system and make symptoms worse.4
- Avoid inverted movements like handstand pushups or GHD sit-ups which can put more, unwanted pressure in your head.
- Scale back on heavy weights. Even though heavy weightlifting doesn’t get you out of breath, it requires a lot of your body's recovery resources – which you should conserve for fighting whatever is making you ill.
When it's not
If you’re feeling any worse than what was described above, I recommend you put the sneakers away. If symptoms are “below the neck”, such as chest congestion, heavy coughing, or an upset stomach, it’s best that you rest and allow your body the recovery it needs to start feeling better.
If you have a fever, or flu-like symptoms, participating in any exercise can be very dangerous. Fevers can decrease muscle strength, impair coordination, and increase dehydration.5 On top of this, intense exercise can raise your internal body temperature which can cause serious problems if you already have a fever.
Immune-boosting tips to get you back in the game faster
If you do find yourself sick this winter, there are some immune boosting tricks you can use to get back on your feet faster:
- Get at least 7-8 hours of quality sleep. Lack of sleep is associated with a suppressed immune system and an increase risk of catching a cold.6 Getting enough sleep will allow your body to recover and give your immune system a chance to win the battle.
- Don’t forget to hydrate, especially if you are still participating in light exercise. Your immune system needs fuel – including fluids – so it’s important to rehydrate and replenish the electrolytes that you lose through sweat.
- Supplement with immune-boosting vitamins and minerals. Adding vitamin D, magnesium, and possibly a garlic supplement can boost your body’s response to infection, increase production of your immune cells and fend off unwanted inflammation.7,8,9
When trying not to let your sickness slow your training, remember: you know your body best. If you think you need rest, then rest! In the grand scheme of things, a few days off will have very little impact on your training. On the flip side, trying to push through a bad cold will only prolong the time it takes for you to get healthy again. Better to rest up and come back stronger!
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 Jamurtas AZ, Fatouros IG, Deli CK et al. (2018) The Effects of Acute Low-Volume HIIT and Aerobic Exercise on Leukocyte Count and Redox Status. J Sports Sci Med.17(3):501-508.
 Martin SA, Pence BD and Woods JA. (2009) Exercise and Respiratory Tract Viral Infections. Exerc Sport Sci Rev. 37(4): 157–164.
 Lee HK, Hwang IH, Kim SY, and Pyo SY. (2014) The Effect of Exercise on Prevention of the Common Cold: A Meta-Analysis of Randomized Controlled Trial Studies. Korean J Fam Med. 35(3): 119–126.
 Gleeson M and Williams C. (2013) Intense exercise training and immune function. Nestle Nutr Inst Workshop Ser. 76:39-50.
 Natalie A. Dick NA and Diehl JJ. (2014) Febrile Illness in the Athlete. Sports Health. 6(3): 225–231.
 Prather AA et al. (2015) Behaviorally Assessed Sleep and Susceptibility to the Common Cold. Sleep. 38(9): 1353-9.
 Martineau AR et al. (2017) Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. Bmj. 356: I6583.
 Laires MJ and Monteiro C. (2008). Exercise, magnesium and immune function. Magnesium research, 21(2): 92-96.
 Josling P. (2001) Preventing the common cold with a garlic supplement: a double-blind, placebo-controlled survey. Adv Ther. 18(4): 189-93.