Tempos are great for building your speed stamina, and they raise the point at which lactic acid builds up in the muscles.
They are ran at a lactate threshold pace- which is roughly 25-30 seconds per mile slower than 5k pace, or a pace you can sustain for an hour in a road race. (I think the pacing is more adequate with the latter target).
Tempos vary from at least 20 min in effort duration, to over 30. Although anything over 30 minutes tends to be targeted more for marathon runners ran at a more moderate pace.
These sessions differ to interval sessions as intervals are used more to refine raw speed. These are ran in and around 5k pace and the reps themselves are more frequent and/or shorter. Recoveries tend to be static and you're looking for more natural pacing progression for most of the session, as opposed to tempos which are ran at even and consistent splits.
Terrain, conditions and how the body is feeling will always determine effort, so listen to it. But a good rule of thumb to know you've paced tempos right is that when you finish the session, if I were to tell you to run a rep again, you could easily do so. You should be satisfied after the session, but not exhausted. Think 'comfortably quick'
Cameron Harris- Head Coach