I have been doing in the last weeks since I got Expedition and before that with Fenix 5, about 4-5 runs per week. Or of these, two are intervals in HR Z4 and fewer in Z5, between 3-10 minutes each, about 3-5 intervals per run.
However, with only one exception I get no anaerobic benefit. The exception was one run two days ago when I got 0.2 benefit after 5 intervals of 8 minutes in Z4.
Is this expected?