Tempo

When training for marathons, I usually think the standard twenty minute tempo run to be too short. If I'm going to be racing for three hours, shouldn't my tempo workouts be closer to forty or sixty minutes?

The way I do longer tempo runs is by using cruise intervals. The purpose of the tempo run is to run at or near your lactate threshold so your body improves its threshold. It also has a mental component where you mentally get conditioned to holding your pace for a longer period of time. Cruise intervals are done by running at your lactate threshold for five to fifteen minutes, taking a short rest interval and then repeating. You could do six repetitions with one minute rest. This would give you thirty minutes at your tempo pace with the rest intervals making sure your body didn't exceed your threshold for too long.

It's a good way to do a longer tempo run without exceeding your limits.