(Explaining how to find the LT pulse with a wattage based test.  ex. start at 120 Watt, increase 20 watt/minute until you no longer can maintain cadence the full minute) 

A:  The LT deflection seldom works I've found.  To find LTHR I recommend that you do 3 things.   

1) Rate your perceived effort (RPE) at every minute on a scale of 6-20 with 6 being very, very light and 20 being maximal.  Around 15-17 RPE you should be experiencing LT.   

2) Have an assistant listen to your breathing trying to note when it first becomes labored.  This *ventilatory threshold* also occurs at about LT.   

3) If you have a power-measuring device available (CompuTrainer, SRM) complete the test going as long as you possibly can.  Then multiply your finishing watts by 0.85 to predict LTHR.   

Between these 3 indicators you should get a pretty good estimate of LTHR

(Explaining how to find the LT pulse with a wattage based trainer, when max. pulse is 190 ) 

Do what Motorola, ONCE, and the USA CYCLING people do.  Take a good guess at your LT wattage (play around on the trainer to see what resistance, gear, and cadence bring you to 170), then run a 15 minute test at that wattage output (on a stationary trainer, it's defined by a particular cadence, gear, and resistance, so you need a cadence monitor), keeping the cadence on the mark, and see what your heart rate does.  If it stays the same, you're either at or below LT.  If it is really hard to even finish, or your heart rate goes up  
throughout the test, you're above it.  Re-take the test as many times (wait a few days in between) as it takes to narrow it down.  It's been my experience that most riders still OVER-estimate their LT heart rate, and that it's a good idea to back off the number three to five beats to get it right.  If you're on a heart rate based program that uses LT as its reference, making that number too high is a big mistake.  Too low is not as bad, and you'll dial it in as you ride.

Stephan Seiler ( the MAPP )

Exercise Physiology Page for The MAPP  

Maximal Oxygen Consumption- The VO2 MAX  

The Lactate Threshold  

Strength Training and Endurance Performance  

Principles of Training- Revisited  

Understanding Intervals  

Understanding Heart Rate and Exercise

Aerodynamics and Cycling

The lactate in your leg muscles will tell you  when you are over the LT pulse level, by the heat sensation and pain in your muscles. When the muscles can't reuse all lactate as energy, and the lactate starts to accumulate in your body, you get the signal from your muscles and your labored breathing. 

( No one can maintain an effort over the LT level more than 30 - 60 minutes. This means that the lower level aerobic training is very important, as it teaches the body to be efficient at supplying energy at lower pulse levels. This efficiency together with a good anaerobic efficiency gives you the edge. )