If we’re focusing on raising FTP or Lactate Threshold power, we need the best metrics to track change in FTP. 5 and 10 years ago, we sent our athletes into a lab or university to get the athlete’s blood lactate and maybe Vo2 max tested. Back then, that was the best way to check FTP repeatedly. With the advent of WKO, Source Endurance is now using WKO5, we have nearly unlimited data capabilities, with every day being a data point tracking your modeled FTP vs 1 day in the lab. There’s still calls for some testing days, but they are way more specific and modeled with way more data than a single blood lactate curve. 


To get complete data, ideally we have maximal and race files across all effort durations. If we do not have sufficient data, then we may ask an athlete to do certain tests to really flesh out a Power Duration curve to its fullest before analyzing what is there to determine FTP and optimized intervals. The paragraphs below outline some shortcomings of lab data vs power meter data and how to look at Vo2 and modeled FTP in WKO. 


The cycling and triathlon training field has changed drastically in the last few years, especially in terms of the data we can collect with tools like HR/HRV monitors and power meters. With the increased accuracy and amount of data we collect from each athlete (and increasingly powerful tools to interpret that data), we may actually be able to do away with some older means of data collection.


VO2 and blood lactate data, in particular, once required booking time at a university laboratory to gather. Now, we can instead interpret your power meter data over time to cover almost all necessary physiological data—and save you lots of time and money in the process.

The Key Metrics and Shortcomings of a Traditional VO2 Test

By measuring the gas inhaled and exhaled, a traditional VO2 test can tell you the power or heart rate ranges where you’re aerobic or anaerobic, as well as the maximum volume of oxygen you can move through your body. If you have a higher VO2 Max, you can move more oxygen, and in theory, you’ll have more power. In the past, we’d get a VO2 baseline, train an athlete, and repeat the test to see if their VO2 rose; if expired gasses showed higher oxygenation or increased efficiency, we could see if the training was working.


The stats from the VO2 test overall (including expired gases and CO2, and RER) can give you some good data, if you know how to interpret it—but the single VO2 max test value doesn’t really help us much, as it’s just a single snapshot from a single day. With ongoing power meter data recorded over time, we can get more actionable data and even get the same VO2 numbers without the lab.

How to Use WKO to Replicate VO2 Test Results

As an alternative, you can use the WKO Power Duration model, or your max powers plotted in a curve for each time stamp from one-second max power to the max power of your longest ride. If you compare your PD curve from one 90-day training period to the next, and the second period shows higher power in your curve, then you’re watching your training work! You don’t need a lab test to confirm that you’re putting more power to the pedals and increasing speed.

FTP Power graph

If we know your size and a given cycling efficiency, we can also estimate your VO2 without the test—here’s a graph of modeled VO2 max based on your Power duration curve from WKO:

Power duration curve

Remember, this data is great, but it’s also important to remember that VO2 isn’t the whole picture of you as an athlete.The goal in training cyclists is to create more power, higher times to exhaustion and be specifically fast for the event we’re training for.

The Key Metrics and Shortcomings of a Traditional Lactate Threshold Test

When you increase your power on the bike, eventually you get to a point where your cells’ regular metabolism can’t keep up with your body’s oxygen needs. They switch into anaerobic respiration, and start to produce acid (lactate) as a byproduct of that anaerobic work. Your FTP, Lactate Threshold and Threshold Power all refer to the point when your body accumulates more acid than it can buffer, and you need to decrease your effort. The higher this threshold, the harder you can work for longer. 


A traditional blood lactate test involves testing blood for lactate at regular intervals during a 60-minute max steady state effort. However, your performance during a 60-minute max effort can be easily influenced by conditions, fueling and mental fatigue, which can throw off the accuracy of the data. Some coaches prefer a 20-minute max normalized power test, and subtract 5% from your average power for your FTP, but this can be skewed by a larger anaerobic contribution to that short of an effort. Worse, a blood lactate test can only confirm that your training is working when compared test-to-test. That’s a massive amount of time and money to get one data point per test.

How to Use WKO to Measure FTP

Again, the Power Duration curve is king, because it takes all of these factors (and more) into account over time, to accurately predict threshold power and time to exhaustion. Again, if you have good power data, or you have the ability to do some specific short testing with your power meter, we can learn your FTP without a traditional lactate threshold test.

_How to Use WKO to Measure FTP

The PD curve above shows the last 90 days, giving us a running timeline of our FTP in WKO based on power results from any ride, workout, field test, or race. Below is an entire year of Modeled FTP. If our athlete’s data had been lab-based, this would look like just a handful of data points, from tests we would just have to hope had been controlled properly. Instead we can see how mFTP builds and peaks throughout an entire season.

Annual FTP peaks
Training Plan 6

Disclaimer, none of the below WKO or TP numbers are from the 2018 U23 road race champion Alex Hoen pictured above.  


As you can see, most of the actionable metrics you’ll want to take into your training can be obtained without a lab test. A lab is great for checking hormones, resting metabolic rates, and body composition, but anything that can be measured and recorded over time with a power meter or heart rate strap can easily be done at home. If you still prefer lab testing, just keep these two factors in mind:

Will My Test Be Accurate?

If you’re going to do a lab test for cycling, you need to control as many variables as possible to make sure that the results are varied and repeatable. Things like your environment, training load, shoes, pedals and bike fit should all be consistent across tests. This may seem like sort of a “no duh” statement, but I see far too many photos on social media of athletes performing very expensive lab tests on flat pedals and bikes not fit to them. 


Look at it this way: with a data-oriented coach and a trained athlete, an increase in a physiological marker of 1-3% is a major win. If that margin can be attributed to anything other than your training, then the test isn’t serving a training purpose.

Blood lactate test

How Will You Use the Data?

If you’re asking your coach, or thinking about booking lab time to test your VO2 or Blood Lactate, first ask yourself, “will this data be actionable?” By actionable, I mean what will this data tell you, and will it change your training? 


One example of actionable data is fatigability, or time to exhaustion. If you can do 350 watts for 10 minutes but after 1500kj or a couple hours of racing you can only do 300 watts for 10 minutes, you need to work on your fatigability. This metric shows up in WKO, but not in a traditional blood lactate test. 


If you’re seeking an improvement in your performance, are there other, broader areas (like recovery or nutrition) you could address first? Are you currently using your VO2 or Blood Lactate numbers to inform your training? What would change about your day-to-day if you start? These are important questions to ask before putting down a lot of time and expense in testing. 


This off season, if you’re looking to make your training as efficient and effective as possible, get a good power meter, and get a good coach. Those two tools (rather than more testing) are the best way to increase your knowledge, training, and results in your goal events.


Zack Allison earned his bachelor’s degree in Exercise Science at Colorado State University. As part of his education, he participated in many hands on exercise science practicum and internships, coaching many types of athletes, specifically cyclists.

Zack’s affinity for cycling started at the early age of 14 racing on the east coast. He quickly moved up the amateur ranks to race on the elite national circuit. This level of competition sparked his interest in exercise science, taking him to Colorado State University. While racing for his alma-mater and on various amateur teams he saw many podiums at the Collegiate Championships and Pro/Am events. Zack is currently living in Fort Collins, Colorado and has raced for Elevate Pro Cycling and currently races for Clif Bar.

Growing up with great mentors and coaches, Zack has a goal of paying it forward. He hopes to use his education and racing experience to bring success to Source Endurance and his clients.