By: Jim Rutberg, CTS Pro Coach
A physiologist friend told me a story about working with an elite wrestling team. She conducted VO2max tests on everyone on the team, and one athlete asked, "How many times a week should I do the test to get better?" A bit surprised, she replied, "No, you go and train, then you come back and do the test again." As it turned out, the wrestling coaches hadn't explained the purpose of testing or the relationship between training and performance testing.
Similarly, endurance athletes sometimes make the mistake of treating every ride or every climb like a test, or neglect testing altogether. Let's take a look at why performance testing matters, when you should do it, and how it's done.
Why Performance Tests Matter
You have to know where you're starting from in order to design training that will make you faster and more powerful. At the beginning of training, or when you first start working with a cycling power meter, it is important to establish a baseline value for at least your lactate threshold (maximum sustainable power output). You can also perform a VO2 max (maximum aerobic capacity) test, and/or a power profile test that establishes values for your best power outputs in specific timeframes (5 sec. power, 30 sec., 1 min., 5 min., 20 min., etc.).
Most power training methodologies (CTS, Joe Friel, Hunter Allen, etc.) calculate training intensities for specific workouts based on the results of performance tests that measure or estimate an athlete's power at lactate threshold. Performance tests need to be completed a few times per year because power at lactate threshold should increase as a result of training, and to continue making progress your training intensities need to be updated to reflect that progress. 
When to Test and Retest
Logically, it makes sense to start a goal-oriented period of training with a performance test. As I'll explain a little later, that test can be in a lab or in the field, which may also affect your ability to take subsequent tests.
Field testing, which is completed using your power meter outdoors or on an indoor trainer, is free and easier to fit into your schedule. It also uses the exact same power meter you're using during training sessions, which is – as I explained in a previous article – important because power meters are accurate to themselves. Lab testing is more exact than field testing because you are actually measuring blood lactate levels and possibly measuring the composition of inspired and expired air, but it is less convenient and can be expensive.
As an example, many CTS Coaches prefer to bring athletes in for two lab tests per year (combined Lactate Threshold & VO2max test at the beginning and end of the season), and conduct field testing about every 12 weeks (3 months) through the season. The interval between field tests should be long enough for an athlete's training to make a measurable impact on his or her physiology, but not so long training stagnates due to outdated intensity ranges.
When analyzing power files on a daily or weekly basis, coaches look to see when an athlete's workload is no longer leading to progress, and often make incremental adjustments between tests, as well. It is also important for an athlete to be rested before taking a performance test, because fatigue from a high training workload is likely to suppress performance when a test is completed in an unrested state.
Lab Testing: Lactate Threshold or VO2max, or Both?
The benefit of lab testing is the ability to directly and accurately measure what's going on in your body. During a lactate threshold (LT) test you ride against a set resistance that increases at set intervals (Ex. 25 watt steps every 4 minutes). At the end of each stage your blood lactate level is measured by analyzing a drop of blood from your finger. There are a few different protocols, but at CTS we stop the test once an athlete has recorded two successive 1 millimole jumps in blood lactate.
A lactate threshold test can be completed with or without a mask and metabolic cart that measures the composition of inspired and expired breath, but a VO2max test requires this equipment. Measuring gas exchange provides values for oxygen consumption and Respiratory Exchange Ratio, which indicates the ratio of carbohydrate to fat you're burning to produce power. The test itself uses incremental steps up in resistance (or pace and grade if running on a treadmill) in one-minute stages until the athlete voluntarily stops (after a lot of yelling and encouragement from everyone in the room).
If you have the opportunity to do both LT and VO2max testing in the same session: do it. VO2max is trainable, although athletes achieve bigger improvements in power at lactate threshold, and measuring both also gives you an opportunity to determine the lactate threshold power as a percentage of VO2max power.
Think of VO2 max as the height of the ceiling in a warehouse. Your power at lactate threshold is how much of the warehouse you're currently using, and the empty space between is what you're working to change. You can raise the ceiling by training power at VO2 max or utilize more of your current potential by raising power at LT (from say 70% of power at VO2max to 80% of power at VO2max). Ideally, you will improve both over time.
Field Testing: Effective and Free
The great thing about field testing with a cycling power meter is that it provides accurate data you can use to establish training intensities. Two popular tests are a 20-minute time trial and the CTS Field Test, which consists of two 8-minute time trials separated by 10 minutes of easy spinning recovery.
Although neither test can be said to measure lactate threshold, an athlete's lactate threshold power correlates with 95% of that athlete's average power from the 20-minute test (Functional Threshold Power – aka: FTP, per Hunter Allen and Andy Coggan), and with 90% of the highest average power from the two 8-minute efforts. This is why either test can be used to accurately calculate training ranges (although the individual calculations are different).
Read more about the pros and cons of these two tests.
Download CTS Field Test Instructions, Intensity Range Calculations, and Workout Descriptions.
Read more about FTP testing here.
When you use field testing, try to keep the variables constant. Use the same stretch of road or same climb. Test in similar weather conditions, if possible. Consider using an indoor trainer if outdoor conditions are likely to be highly variable. And be sure you are rested prior to the test. By keeping as many variables as possible consistent, you can better compare the results of one test to another. 
Keep Testing in Perspective
Like students, some people are great test takers and others are great performers who don't test well. Performance tests are a good way to measure progress and adjust training intensities, but at the end of the day, test results don't win races.
By analyzing your power data frequently and consistently, you can make incremental adjustments to training intensities and workouts as needed, and use periodic testing as a confirmation that you're on the right track.
Jim Rutberg is a Pro Coach for CTS and co-author of "The Time-Crunched Cyclist" and "Training Essentials for Ultrarunning."
For more information about coaching, training camps, and Bucket List events, visit www.trainright.com.