Mona,

It can be either speed or inlcine.

I myselg use speed as my levels for the most part, but I have done some where I will jog at a constant speed and then just up the incline.

The levels BFL talks about do not translate into MPH speed on the treadmill.  Your levels 5 and 9 will be different than other people's levels.

Hope that helps and good luck.

Thanks for the input. That makes sense :)

I agree with Rick. Speed is what you want to achieve with cardio. You dont want an incline that then makes your quads work out - you did LBWO yesterday and they need to rest.

I have been using my Gazelle for cardio - for fun I can squat a little to work my quads, but on cardio days it is all about speed and stride length for me.

Mona-This is what I had posted for someone else the other day...keep working hard and gradually increase your speeds and before long you will AMAZE yourself!!

When I first started the challenge back before Christmas my speeds for the intervals were:

2 min. @ 3.5 mph (this is at 0 incline), then 4, 4.5, 5, 5.5, and I tried 6...These are my words I used when I wrote in my journal:"First HIIT...OMG! Kicked my butt! Couldn't do last 9.5/10. Think I started out @ too much..." The next HIIT I dropped it down to 3.5, 4.0, 4.2, 4.4, 4.6 with a 10 at 5...was more manageable cause I was in TERRIBLE shape. I look at that now and feel so happy of where I have come.

Now I'm almost finished with C2 and I start at 4 mph for 2 min. then 5.2, 5.7, 6.2, 6.7, with a 10 @ 7.5/8! I encourage you to write in your journal how you felt so you can gradually increase the speeds.

I was proud of myself because I've never ran - ever, on or off the treadmill. So for me to last the whole 20 minutes doing HIIT showed me that I must really be getting into some kind of shape!

Take care!

I'm new on the treadmill, only been on it twice (I'm in week 10) but here's what I do:

Level 5 (twice) speed 3.5

Level 6 - speed 4

Level 7 - speed 4.5

Level 8 - speed 5

Level 9 - speed 5.5

Level 10 - speed 6

Back to level 5 - speed 3.5

So you could start out at a low number or go up in smaller increments 3 - 3.2 - 3.4 - 3.6 etc.

Experiment to find what works for you!

Have Fun!