I did a Z1-Z2 run last week, and I was startled to see my heart rate go to the high part of Z2 in the first 4 mins of my Z1 warmup…
I train in power (but also recording HR, pace, and GPS) and while this was a run up hill in my Z1 warmup, my power and pace were both controlled and solidly in Z1 while my heart rate jumped up almost to Zone X and stayed elevated for about 3 mins before dropping back down. Weather/temp was not an issue – it was neither hot nor cold. I think I’ve seen this early HR spike before, what’s this all about?
Hard to pin down. It’s just part of the nature of HR and is not an uncommon issue reported by athletes.
If you are watching TV and I stand behind you and say “boo!” your HR can jump to Zone 2. Clearly, it’s not due to intensity, it’s due to other systems. We just don’t know what your body is doing in the “background” sometimes. Stress, sleep, hydration, or as Ebenezer Scrooge might say “a fragment of an underdone potato.”
If your HR crosses 2 zones (you’re in Zone 1 Pace/Power but Zone X HR) then back off. Otherwise, I’d reply on Pace and Power and let HR do it’s thing.