First time poster here so please bear with me if this question has already been asked.

I have a bad lower back from when I was in the Army and am not able to do more than five minutes of high impact (running, jogging, etc) activities without my back starting to act up.

Ive been back into the gym for a month now and feel that Im ready to "take it up a notch". Currently I do 30-45 minutes on an elliptical 4-5 days a week and do resistance training 4 days a week, and 15 minute warmup on an eliptical on my resistance days.

My question is, is there a way of doing HIIT without having to do sprints or running? I know Im reaching here, but if I exerted maximum effort on an elliptical, would that be considered HIIT?

Yes, that would do just fine. So long as you follow the "rules" of HIIT. Check the sticky for more info.

Yep, it's fine. You can hop on the bike instead, too.

Thanks for the replies. Today I did 10m warm up, then did light shoulder work and did my first HIIT session!!
I started with a minute of warmup on the elliptical machine. Then i did intervals of:
15s sprint
30s moderate
For maybe 3 cycles.

I didnt feel like i was recovering fast enough so I changed the intervals to:
30s sprint
1m moderate
for another 6 or 7 cycles

It pretty much kicked my butt!
Now, since this is considered an anaerobic excersize, should one also be doing some form aerobic training on the same day as well?

Oh, an observation I made after HIIT for you newbs (like myself) out there is this - even though my total time on the elliptical was roughly 10min give or take a minute or two (which is all Im able to do my first time), the machine displayed that I still managed to burn 120 calories! I know, take that reading with a grain of salt, but heck, I usually do 30 minutes at a moderate speed and I end up burning around 300 calories, so if you do the math:

HIIT - 10 minutes/120 cal = (10mx6) x 120 cal =720cal/hr
Aerobic - 30 min/300 cal = (30mx2) x 300cal = 600 cal/hr

Yeah, I know, its pretty obvious considering the effort you put into HIIT, but hopefully by pointing it out and looking at it from this point of view, it will turn more people on to do it!