In these low intensity aerobic zones the distinction between Recovery and the bottom of Z1 is not well defined. Meaning, there is quite a bit of overlap in the HR zones and even the training effect. Think of these zones this way: Z2 is the maximum intensity that is still predominately aerobically fueled by fat. So, the best intensity for increasing aerobic this basic aerobic quality. Z1 is best thought of as aerobic maintenance (rather than building). Recovery can be anything from a very easy jog to even a brisk walk. It’s purpose is to speed recovery to get you back to training (building fitness) as soon as possible. These need to feel very easy and leave you feeling better at the end that you did when you started. I’d suggest using Z1-2 in place of those suggested recovery runs. But need to base this decision on how tired you are feeling. Use a recovery workout when needed.