It would help to specify if you mean miles or km. This changes the answer significantly.For a first time marathoner who plans a 6:10 min/km pace, targeting a 4:20 marathon, the objective is most likely just to finish, and may as well just do all of his runs at "easy" pace simply to develop sufficient endurance. Tempo runs and speedwork are not vital for this first time marathoner.But I guess you mean 6:10 km/mile, targeting a 2:41:41 time. The answer then depends on your principles.There is a principle of specificity, which says that only paces around a race pace specifically benefit that race pace. My rule of thumb is +/- 20%. This means paces from 5:00 to 7:30 min/mi. should still provide some specific benefit. Outside of that, the training takes on a different purpose (e.g. general recovery, or for sprints)For a 6:10 min/mi pace, 5:30 is about 10K pace, and 4:50 is about 1600m pace.There is another principle of balance. You can surely put in a good marathon performance strictly on tempo runs, progression runs, and long easy runs. But at some point, strength and speed (and form?) become your weak points, and the remaining improvements will come from developing these weaknesses.One last "rule of thumb" I've heard. For your first marathon, you should add 15 minutes simply due to inexperience of race pacing.
first time thoner wrote:
If you plan on running, say, 6:10 pace for a marathon, how beneficial is it to do shorter repeats (1000m - 2miles)at sub-5:30 pace. I'd imagine that it would probably help your performance more doing longer progression runs and tempos at slightly below Marathon pace (6-5:50?)- maybe doing a few quicker repeats a week or two before the 'thon would help, but I find it tough to believe that faster stuff is vital for a good marathon performance.