A tempo run is a sustained effort at a comfortably hard pace, faster than easy running but not an all-out sprint, usually held for 20 to 40 minutes. It's designed to raise your lactate threshold, the pace you can hold before fatigue builds up quickly. Runners often describe the effort as hard but controlled.
It's a sustained run at a comfortably hard, controlled pace, faster than easy running but well short of a maximal sprint. It's typically held for 20 to 40 minutes within a longer run.
A common guide is roughly your current 10K to half marathon race pace, an effort you could hold for about an hour if pushed. It should feel challenging but sustainable, not a struggle from the first minute.
A tempo run is one continuous, sustained effort with no rest breaks built in. Intervals alternate hard efforts with recovery jogs or walks in between.
Once a week is typical for most marathon and half marathon plans, often replacing one of the easy runs. Overusing them without enough easy running increases injury and fatigue risk.
It raises your lactate threshold, the pace at which fatigue starts building up faster than your body can clear it. A higher threshold lets you hold a faster pace for longer in a race.