HIIT has nothing to do with switching up what your doing... its 110% intensity... to a low 10-20% intensity... and back and forth within time periods. To me swinging a sledge hammer or kettle bell doesn't work because of my back... but an elliptical going from slow and chill at level 1, to a burst at level 15 all out, back and forth worked super well and minimized any type of injuries. i mean do whatever you "enjoy" most, but over the years I've learned that fine tuning and focusing on what the "job is" instead of being all fancy pays off much more. the goal is raising your heart rate as high as possible and using as many muscles as possible.. but at the same time i like to think with the least amount of stress on your joints and stuff..
i used to sprint and do hill runs and all sorts of random things to try and lean out.. and when i cleaned my diet up and made it 100% perfect... i could get on a treadmill and walk like an 80 year old man and lean out.. and i have bad genetics lol. if your body fat is above 10% .. i would use as minimal amount of stuff per week to see weight loss.. when that weight loss stops.. make adjustments and try to shave an additional 500 calories a day off... this is where a lot of people screw them selves... me included...
they go into something say 15-20%+ body fat... and they wanna get shredded so they take every fat burner, pre workout, steroid etc.... then they cut their calories to 2000... then they do 6 mornings of cardio and lift 5 nights a week. almost exactly what i did.. and although i leaned out fast.. i got to about 10% body fat... and had no room to scale out calories... or add in more workout routines.... so pace your self.. start just with eating clean and lifting and not doing much cardio.. wait for your body to catch up and make its changes and stop your fat loss... etc..... then shave 250 calories and add 20 minutes of cardio.... then 2 - 4weeks later.. probably do the same thing... and so on.. its going to get to a point where you are quite lean and ripped.. then .. u back off and try to locate your maintenance calories.