I’ll be 52 this month and have been following TFtNA for years. Recently, I’m finding that my heart rate is spiking into Zones 3 and 4 at the outset of my Z1/Z2 runs. I’m not running materially faster at the start than I am at the end, and I’m not even heavy nose breathing at the outset. HR drops quickly if I slow to a walk but then spikes up again the moment I start striding it out. After about five minutes, it settles into Z1/Z2. This is quite new for me– I even thought it was my TICKR malfunctioning, but the reflection of the downward tick when I slow seems to indicate it’s working fine. Any thoughts on what’s going on? Do I just power through that first five minutes at the elevated rate? Do I go slow-normal/slow-normal? Do I just walk for the first five? Appreciate any guidance here. Not sure it matters: my max HR has been in the 190s for years but, just recently, I noticed heavy nose breathing at the top of my Z1. I retested max HR to find it had dropped into the 170s and recently readjusted all of my zones accordingly.