Radon test results came back as 1.7 pCi/L, is it safe to exercise in my basement?
As you have probably learned doing research, there isn't a hard-and-fast cutoff between "safe" and "dangerous". But 2.0 pCi/L seems to be the threshold for considering remediation, and that's for a living space. If you're using the room for exercise you'll probably only be spending a few hours per week there, which would dramatically reduce your exposure.

Personally I wouldn't worry about it.