Thanks Alex. I did a search and found quite a few posts about hr workout. Let me go through the ones I think that can help me. To tell you the truth I realized that changing the target hr on the fly is maybe easier. Whoop suggest me a time and target hr. I just write them down on a piece of paper and look at the timer. When it’s time to change target I just press the up or down arrow.
I like more old school training like this. Many pros still use this technique outdoors.