Demystifying Lactate Threshold

For VeloNews

Demystifying Lactate Threshold

© 2006 by Joe Friel and Doug Bush

With the advent of sophisticated training tools such as GPS, power meters and heart rate monitors it has become increasingly confusing for athletes to determine training intensity zones and to monitor fitness.  The old adage of riding as much as you can, as hard as you can is being replaced by the mantra of precision.  Athletes and coaches are developing detailed, periodized training plans based on very specific training intensities. 

Lab and field tests are excellent tools for establishing training zones as well as monitoring current levels of fitness and for making training adjustments before important races.  The key to such testing is finding your lactate threshold.  There are many ways of defining lactate threshold (LT), but simply put it is the intensity at which the muscles produce lactate faster than it can be metabolized. 

LT and Muscle

Lab and field testing are simply ways of determining which muscle fibers are utilized and the energy system supplying them at various intensities.  LT should correlate with the point at which fast twitch muscle fibers are first employed and the body begins to rely more on carbohydrate than fat as an energy source. 

Muscle consists of three main categories of fibers, — slow twitch (Type I), fast twitch (Type IIb), and a group of fibers that share properties of both of slow and fast fibers (Type IIa). These fibers are recruited to help carry the load in a very orderly fashion as exercise intensity increases starting with Type I. The next fiber type is not called on until all of the preceding fibers are in use.

Once LT is determined by testing training zones can be developed. These zones are specific to cycling and based on information in The Cyclist’s Training Bible.

The point at which LT occurs in relation to VO₂ max is a great snapshot of fitness.  In sedentary people LT usually occurs at about 50% of VO₂ max while in elite athletes during peak form it is not unusual for LT to be around 90% of VO₂ max.  For most active cyclists a range in LT from 70% to 85% occurs throughout the season depending upon the type of workout and training volume.  Because lactate threshold in relation to maximum varies from person to person and throughout the season, basing training zones upon heart rate maximum is not the best method.

The most precise methods for establishing lactate threshold are with lab tests using a metabolic cart to monitor expired gases or with blood samples measuring lactate.  These methods of testing can yield quite accurate results, but blood sampling can show wide ranges of variability based on where and how blood samples are taken as well as the testing protocol and equipment used.  Due to the extremely high cost of testing equipment, in the past expired gas testing (VO₂ testing) was available only to elite athletes and subjects in university-sponsored studies.  Fortunately many commercial testing centers and coaches are beginning to offer expired gas testing for all levels of athletes.

Lab Testing

Blood lactate testing has often been considered the gold standard for determination of LT.  When done correctly it yields quite accurate results.  Unfortunately, blood testing is susceptible to errors based on blood draw location, exercise test protocol, as well as type of equipment used for the measurements. And getting blood drawn during an exercise test is not for everyone.

Expired gas testing measuring oxygen and carbon dioxide when performed correctly can also yield accurate results.  This test has been primarily used for measurement of VO₂ max but  can also be used to determine anaerobic threshold.  Some physiologists argue that anaerobic threshold and lactate threshold are different, but a large body of research supports them as being the same.  Expired gas testing is much less painful than blood sampling. as the gases you breathe are captured and measured while you wear a mask attached to a gas analyzer. 

Your caloric expenditure at various intensities, fat and carbohydrate utilization during exercise, cycling efficiency, and more can also be gleaned from an expired gas test.  The downside is that expired gas testing can be a bit expensive as the equipment costs tens of thousands of dollars.

Field Testing

Field tests are a great way for an athlete to measure fitness as a supplement to being testing in the lab.  All tests should be preceded with at least a 20-minute warm up including three to four 30-second intervals at the planned test intensity on a track, indoor trainer or road course with little traffic and no intersections.

The 30-minute time trial is the field test we use. It is very useful to estimate both LT power and LT heart rate.  The effort for this field test should be all out but it is best to start out a bit easier and really try to increase effort over the last 20 minutes.  Average heart rate and power over the last 20 minutes is a good estimation of lactate threshold.

Other Methods

Tests based on maximum heart rate and heart rate or power deflection point (often referred to as a “Conconi” test) have also been used in the past to estimate training zones.  Using max heart rate equations or actual maximum can be inaccurate as these do not account for the variability of LT.  Maximum heart rate equations assume that everyone’s lactate threshold occurs at the same point relative to max heart rate, which is just not true.  A substantial amount of evidence in reputable journals has questioned the validity of using the Conconi method as a deflection point is not found in the majority of test subjects.

Determining lactate threshold can be useful information for an athlete before and during the race season.  It is important to reevaluate lactate threshold periodically throughout the year as values can change.

Joe Friel is the author of The Cyclist’s Training Bible and the founder and president of Ultrafit Associates coaching group. Doug Bush is a coach, exercise physiologist, and member of Ultrafit.  More about Doug and Joe may be found at www.endurancefactor.com and www.ultrafit.com.