I already have one day designated to hill sprints, but instead of doing 2x week hills, I want to add a 2nd day of either just flat track sprints (100-400m) or HITT (jog curves "sprint" straight for 2-4 miles). Which would be better to do for just overall conditioning, fat loss and grappling? Sprints I can go 100% each with rest. HIIT obviously you try to sprint, but you get drained and can't go 100%. I also do long steady runs 2x week or so along with tire flips in as well.