Lactate threshold causes a lot of confusion for athletes trying to determine accurate training zones. Threshold can be determined with several methods, but understanding the implications of each and how they relate to determining individual zones is vital.
Two common methods for testing lactate threshold and determining power and HR training zones are:
1). A graded exercise test in the lab measuring blood lactate and
2). A time trial field test.
So what's the difference?
Should you use lab test data for prescribing training zones or use the average power/HR obtained in an all out time-trial?
The Lab Test
First, let’s discuss each test and what they actually measure. In the lab test periodic blood samples are taken from the fingertip or earlobe as an athlete exercises at a gradually increasing intensity. The test starts easy and increases 15-30 watts every 3-4 minutes. At the end of each stage a blood sample is drawn. Each sample measures the lactate response to a given workload.
With each workload the lactate will rise linearly as a result of increasing carbohydrate oxidation. However, sooner or later your lactate will start to rise very fast and break from this linearity - this is typically termed the lactate threshold. This rapid rise typically occurs around 4 mmol of lactate but can range from 3-6 mmol. This is the point where the production and burning of carbohydrates for fuel occurs so rapidly that the body’s clearance system cannot keep up and lactate begins to accumulate. The workload where this shift occurs is defined as the lactate threshold and used to define training zones for our athletes.
The Field Test
During a field test athletes complete a 10-20 minute time-trial effort as hard as they can. The average power and HR are recorded and training zones are based on a certain percentage of these averages. The single best predictor of endurance cycling performance is the average power one can sustain for about 60 minutes. In order to predict what they could do for a 60 minute time trial using a 20 minute test, we only take into consideration 95% of the power that they can average for 20 minutes.
Beginner cyclists who do not have much experience pacing for longer time trials typically do better with shorter efforts. In this case, you can do shorter 3 mile time trials and take 90% of the average to determine their training zones. You should note that the shorter the test, the larger the potential for error. This is due to the larger relative percentage that anaerobic power plays in determining the result, i.e. 2 minutes of anaerobic power is more than 20% of a 9 min test and less than 10% for a 20+ min test.
The Breakdown
Both methods are relevant ways to determine training zones. Average power during time trial efforts lasting about 60 minutes correlate very well with the results found in a lab test. However, many cyclists do not do 60 minute time-trials. It is typical to see threshold power determined from a TT test higher than that of a test taken in the lab.
A field test is simply a method to estimate the individual lactate threshold you would get from a more accurate lab test. The reason these values do not always match up is that your OBLA power is highly correlated to the power you can maintain for 60 minutes, not 20 minutes.
The bottom line is this: if you choose not to use a lab to determine your training zones, keep in mind that the shorter your field test is, the more disparity the results may have from a test done in the lab. Having accurate threshold values and a knowledgeable coach will go a long way towards improving your fitness and getting the most out of your training.
Chad holds a Master of Science degree in Exercise Physiology and a Bachelor of Science in Exercise Science/Cardiac Rehabilitation from Ithaca College. He is a certified Health and Fitness Instructor with the American College of Sports Medicine and has over 10 years experience coaching, testing, and consulting individuals. Chad is a USA cycling certified coach and has been published several times in The Journal of Medicine and Science in Sports and Exercise. Visit www.enduranceWERX.com for more information.