While scientists debate which theory to follow, here’s what we know and how to think about it:
Regular exercise practiced over time is beneficial to the immune system. It will make it more robust.
But like with performance, if you push into or near over-training, your risk of infection likely goes up. It’s not rocket science. It’s stress and adaptation.
Rather than defining hard/moderate/easy for your training, think of it as drastic changes which alter your risk of infection. If ‘normal’ for you is running 10 miles per day and you continue doing that, you’re likely fine. If normal for you is running 2 miles per day and you try to run 6 miles per day, your risk of infection likely goes up.
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