Two zone 2 workouts can have very different heart rate profiles. During the first one below, it felt like it took me a long time to warm up, and was then a struggle to stay above 70% MHR. In the second one, my heart rate jumped right up to zone 2, and the workout felt easy, despite being at the upper end of the 70-80% range.
I don't really have a good explanation for what is going on here, if anything. The frequency of workouts for both sessions was only about 2-3 per week, and I didn't make any changes to my sleep or fasting schedule. Neither workout was fasted.
