30 Day Shred calorie burn differences between levels

fhttrs

So I wear a heart rate monitor during my 30DS workouts. I'm on day 3 of level 3 and I've noticed that my calorie burn is significantly less than level 2 and even today less than my norm for level 1. I'm wondering if that's because level 3 is more (or at least seems more to me) strength-based. I feel like I was really pushing myself cardio-wise (and thus my heart rate skyrockets since I am very out of shape) during levels 1 and 2 and for level 3 its more of an "oh my god my arms are burning" feeling for the most part.

When I went from level 1 to 2, my average calories burned went up about 50 for the 28 minutes. Now it's dropped about 20 from level 2.

There's also definitely the possibility that it's really just that much harder and I'm not able to push myself as much. I've been getting terrible exertion headaches for the past three days so I guess it is a possibility. They always start during the same part and then last through until about 3/4 of the way done. My head just POUNDS and drinking water/trying to focus more on breathing/etc. doesn't seem to be helping that much.

I have noticed, however, that as the calorie burn decreased, my HRM is showing that I'm spending more time in what it considers a "fat burn" heart rate zone rather than my heart rate being skyrocketed for most of the time. I was getting sub 3 minutes of the in fat burn during level 1, between 3 and 5 in level 2 and now on level three today I was almost at 11 minutes of fat burn for the 27 minute workout. I'm sure that its because during the 2 minute cardio sessions and some of the strength sessions my heart rate still skyrockets up to the high 160s/low 170s and during the ab section it'll drop back into my "zone" (~120-140).

So I'm not sure if the decreased heart rate / lower calorie burn is a good thing or not... Or if I just need to push harder.