I had COVID and even exercised with it. I noticed a higher level of muscle soreness, and in fact that and anosmia tipped us off to what was happening. This was one of the early variants where flu like symptoms were rare.

In my N=1, any one of the myriad other common colds that I've had caused similar symptoms. The degree of muscle soreness was strange. Along with another person in my bubble who also got infected, we both measured increases in red blood cell count outside of the normal range several months after. It wasn't clear if this was due to COVID-19 or being athletes. I didn't have a baseline unfortunately.

I had a dramatically different experience with a flu that I got in December 2019. My resting HR was up by 10bpm for a month after. My exercise regime was broken, and it took almost two months to fully recover.

I truly hope that COVID-19 is just a window into these infection disease processes that are going on all the time, damaging our bodies without giving us clear feedback. This massive pulse of naive infection is a unique opportunity to understand this. I fear that we will not be able to generalize these lessons. And I understand why. COVID is very weird...