You know that feeling at the end of a marathon or long runs where your legs tighten and grow excessively fatigued, like you're running in cement? Blame it on lactate acid, a by-product of burning sugar for energy in your leg muscles. Is there a way to prevent this from happening? So they say: It's training at a "lactate threshold" pace.
What's that? It's more or less your 5K pace, plus 20 to 40 seconds a mile, or your 10K pace, plus 10 to 20 seconds. Top coaches believe you should regularly do 20- to 40-minute runs at your LT pace (tempo training), to increase your body's ability to transport lactate out of the muscles and prevent cement legs. For example, yesterday I ran 4 miles at 9:00 pace (36 minutes), a pretty good tempo run at this stage--and jogged home another 4.
In our schedule, I built in intervals (3rd session) and time trials for speed work, but not enough tempo runs. Tempo runs should be another option to mix in. The upcoming Marathon Pace runs (we have two 4-milers this session, at 8:40 pace) will serve as rather quick tempo runs for this session. (See Runners World, May 2005.)
Obviously, if tempo runs help the body become more efficient at moving lactate, the last 10K shouldn't be as stressed.