Training with a HRM, note sure what to make of recent ITT stats
Ok, so when I first got my HRM, the first thing I did was what Friel suggests. A good warmup, then a 30 minute time trial like effort on my trainer at home and record my heart rate for the last 20 minutes of it. I did that back in the fall and my average heart rate came out to 168. My max was 183. I then based all of my training zones off of that and begun my winter training.
Fast forward to 3 weeks ago. I do an indoor TT. Did a nice warmup like before, get ready to start, have my HRM start recording and go. 23 minutes and 29 seconds later, I finished and come up with an average heart rate of 184 and 193 for a max. I think its just a fluke and I don't adjust my training zones
Fast forward to yesterday. I do another indoor TT. 22 minutes of suffering like before and my average heart rate now comes out to 187 with a max of 195.
Is it time to adjust my training zones? Also, does anyone have any clue as to why this would have happened?