What's the Right Way to Find LT?

QUESTION: I've read conflicting advice on how to determine lactate threshold (LT). One way says to ride a 10-mile time trial on a flat course, and your average heart rate is your LT. I've also read that it should be a 25-mile TT. Other books say that 80% of max heart rate is LT. Finally, I've heard that you should multiply your average heart rate for a one-hour time trial by 0.87. Many training programs are based on LT, so which is the correct way to find it? -- Robert B.

COACH FRED: You're right that lactate threshold is important. The key to successful training is to do a significant portion from slightly below to slightly above your LT heart rate.

One problem, however, is that there are two definitions of LT.

First is the lab definition. LT is the level of exertion that causes your blood lactate level to reach 4 millimoles. There's nothing sacred about 4 millimoles that I can determine, but it's the number that has been agreed on.

This lab LT usually results in a heart rate quite a bit lower than the highest heart rate you can maintain for an hour -- the standard on-bike definition of LT. Hence, the disparity.

Most training plans that are based on LT use the second definition because it reflects what happens in the real world rather than in the lab.

For most of us, average heart rate during a full-out 10-mile time trial, minus 3-5 beats, gives a good number on which to base LT training. Techniques and workouts are covered in depth in "Spring Training for Roadies."