I've been dabbling with spending the last 3-4 minutes of my treadmill sessions walking backwards on an incline. I haven't done enough to see results, I've done

I've been dabbling with spending the last 3-4 minutes of my treadmill sessions walking backwards on an incline. I haven't done enough to see results, I've done maybe 5 sessions so far. One thing that surprises me is how much it gets my heart rate up, I'll do an incline of 10 and a speed of ~2, and usually it'll keep my heartrate in the 150s. If I've just been walking rather than jogging, it'll usually go up.