One of the reasons I like HH plans (n.b. I've only actually used the marathon one) is that compared to some other plans I've seen, they are fairly simple and tend to err on the side of caution, which is probably a good thing, and I remember treating the marathon plan as a sort of template to play around with. So if you're feeling particularly good maybe you can progress the race pace run to 10k or so.
As a rough rule of thumb, I've generally found that a tempo run of half race distance, at target pace, is a reasonably tough work-out in the middle of training. So ~10k @ HMP, 12/13 miles @ MP would be some of my tougher sessions. If they're feeling too comfortable, you could probably revise your target pace.
One of the reasons I like HH plans (n.b. I've only actually used the marathon one) is that compared to some other plans I've seen, they are fairly simple and tend to err on the side of caution, which is probably a good thing, and I remember treating the marathon plan as a sort of template to play around with. So if you're feeling particularly good maybe you can progress the race pace run to 10k or so.
As a rough rule of thumb, I've generally found that a tempo run of half race distance, at target pace, is a reasonably tough work-out in the middle of training. So ~10k @ HMP, 12/13 miles @ MP would be some of my tougher sessions. If they're feeling too comfortable, you could probably revise your target pace.