A tempo run is a sustained effort that’s hard but controlled. The word gets used a little differently across training plans. Here, I’m talking about a run at lactate-threshold effort, often described as “comfortably hard”.
That doesn’t mean running flat out. In the Daniels approach to threshold training, the continuous part of the workout is usually around 20 minutes. The roughly one-hour effort sometimes used to describe threshold pace refers to what a runner could sustain in a race, not how long every tempo workout should last.
Why include tempo runs in our training?
The aim is to build endurance at a demanding effort. Pace will vary with fitness, terrain and conditions, so effort matters more than holding on to a particular number. V.O2 has a useful explanation of threshold effort.