HIIT Calorie Burn Estimation?

mngrsh

Hello, I've recently purchased a Polar FT4 HRM and loaded it with my information (5'0", 132lbs, 19 years old).

I've attempted estimating calorie burn using my average heart rate during the duration of the HIIT session and it seemed completely absurd, so I am rather lost with logging the calories burned for a HIIT session on MFP. I am aware that HRMs are not particularly accurate with estimations of caloric burn during work-outs that are not steady-state cardio and that it is relatively impossible to measure EPOC with one. I haven't been logging my HIIT work-outs at all because of this. I am not too worried about 100% accuracy (since calorie counting in and of itself has some degree of estimation and inaccuracy as well), but I guess I'd like to know at least what I'm burning during the work-out, and not necessarily after the workout.

Example:
Max heart rate during work-out: 100% or 200bpm
Average heart rate during work-out: 90% or 180bpm
Duration: 18'30"

20s work, 40s rest on 75% resistance and 50% resistance respectively for 12 minutes with 3 minutes warm-up and cool-down on an elliptical.

My HRM tells me I've burned 187 calories, whereas using the equation ((-20.4022 + (0.4472 x HR) - (0.1263 x W) + (0.074 x A))/4.184) x 60 x T, I get the number 238 calories, which sounds ridiculous for an 18 minute workout.

Does anyone have a solution to logging calories for interval training? Thank you very much!