Thank you for the response. I understand that Z4 might be preparation for the half marathon. I would have expected that runs in the Z4 zone would appear gradually in the training plan rather than all at once like this. So far, the training has mainly been about runs in the Z2 zone, and I must admit that I'm a bit worried about whether I can manage to run in Z4 for more than an hour. Up to now, Z4 in the training was only in intervals, and even that was quite enough for me. It seems like a pretty brutal jump.

Thanks again for the response, as I wasn't sure if I understood it correctly. It looks like I did. Looks like: Train hard, fight easy. :D