I’ve always noticed that when I’m running on a treadmill, my HR tends to drift up far higher than it does when running outdoors. For example, the other day I ran RRe4, and despite my pace being well within my Z1 range, my HR was up at the top end of ZX by the end of it, and the perceived effort was certainly trending upward towards ZX effort range. At first I thought my treadmill calibration was off, but I timed & measured, and it’s pretty much spot on with what it’s set to. I usually run by pace, but should I instead run by HR indoors? What’s recommended in this situation?