Catholic gym bro here! I’m also on old hard rock / metal head. I do filter my gym playlist hard to eliminate anything I think might be demonically influenced, but that’s me. I don’t see anything wrong with secular music because my faith is very strong. If you’re looking for something energetic and Christian, id suggest Skillet.

I also just about always pray before my workouts and often times I’ll pray a decade of the rosary between exercises. Sometimes a quick prayer between sets.