There could be a number of reasons why you may feel like you’re sick or coming down with a cold — or worse — after a workout, particularly after taking part in some resistance training.
But some of it may have nothing to do with the workout at all.
It’s possible that your body may have been fighting something off in the days leading up to the workout. The type of workout may also play a role.
The Immune System
Anytime you experience muscle soreness, the body’s immune system gets activated to try and repair those sore muscles. And when the immune system becomes activated, we may feel fatigued or like we’re coming down with a cold or the flu.
I’ll start by discussing the type of workout first. Researchers are discovering that the immune system takes a slight dip after performing high-intensity interval training. This means the immune system may not function as well immediately after this type of activity.
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Luckily, this is temporary.
But let's say your body was fighting something off before you performed your sprints or CrossFit workout. It’s possible that, if the timing is just right, that bug may take advantage of the fact that your immune system is temporarily hindered and cause you to feel under the weather.
Before you swear off high-intensity interval training, know that this drop in your immune system’s effectiveness is temporary. In fact, these same researchers have found that after this time has passed, the immune system rebounds and is even stronger than before.
Build-Up of Lactic Acid
Now, there’s another potential reason why you may feel out sorts after a workout, particularly after high-intensity interval training and even resistance training.
I’ll explain: imagine you’re sprinting really hard across a field… besides your heart feeling like it wants to explode, at some point, your legs will start to feel like they’re on fire. This burning sensation is caused by the build-up of lactic acid, also called lactate.
When we perform high intensity exercises like sprints, high intensity interval training, and particularly when we lift weights we can experience lactic acid build-up. This build-up of lactic acid can irritate the muscles and lead to muscle soreness.
When our muscles feel sore, it’s because they’ve been torn up a bit.
Now don’t get me wrong — so long as these muscle tears are minor and not permanent, the body will repair them. In fact, when the body repairs these small muscle tears, the muscle actually gets larger.
However, this process takes a slight toll on the body. Our immune system gets activated to help make these repairs to our muscles. Like I said, if the immune system begins to wake up, we may start to feel like we’re coming down with something.
Avoid Feeling Sick: Stay Hydrated
I should also mention that if you do experience soreness after a workout, hydration is super-important.
This is because some of the byproducts of muscle soreness can cause damage to other organs, like the kidneys.
When some folks hear about this, they misinterpret what I’m saying and think that they should never ever workout to the point where they feel sore the next day.
That’s not what I’m saying. Instead, if you do feel sore, just be sure to pay more attention to your water intake. This will help the body flush out some of those byproducts.
Stretching after a workout can also help remove these byproducts. It’s also a good idea to gently work some of those sore muscles through some gentle stretching or even a light cool down workout.
I discussed warm-ups and cooldowns in another episode.
The following video is a cool down workout by FitnessBlender.
The following video by Chloe Ting is a deeper, 10-minute stretch:
This will bring blood that’s rich in oxygen and nutrients to the sore muscles and help them repair faster.